The Lancet published an editorial in 1931 summarizing the different opinions about Calmette's BCG vaccine against tuberculosis. TB is a serious disease, so having a vaccine would be great, but not everyone agreed that the BCG was that great.
Calmette and those who supported him claimed the BCG was safe and effective. According to Calmette, 336,000 children in France and >1 million worldwide had been given the BCG over 5 years, and this had reduced mortalities from TB from 15.9% to 3.4% in children under 5. Even Calmette recognized that the BCG didn't provide permanent immunity, but he thought it was good enough to get children through the period of life where risk from TB is highest, in the early years.
Additionally, BCG supporters claimed that these bacteria, though still alive when used in vaccines, were safe and innocuous. They could produce lesions, sure, but no serious cases of tuberculosis. Many did animal studies that agreed with this claim.
On the other hand, many other medical practitioners and researchers found the claims more questionable. According to studies in cattle, guinea pigs, and monkeys, the BCG didn't seem that reliable in terms of safety or efficacy. Some of them thought they found animals dead from TB after inoculating with BCG, and some thought the BCG bacteria might increase in their virulence (ability to cause disease) after being grown in animals for long enough. And even previous studies on this blog found that Calmette's recommendations (feeding newborns BCG) didn't seem to work well, at least in animals (056).
So health professionals in Britain set up a special investigation of BCG, with not-great results. They decided that Calmette's good results could've been due to fallacies and biases and inadequate controls; for example, without blinding and placebo, it's possible that receiving the vaccine could've correlated with better care of the children in general, maybe because only cautious parents volunteered for the study or something. So hard to conclude anything. Also, some animal studies seemed to say it wasn't good, while others that it was.
Also there was a tragedy around this time in Lübeck, Germany. Many infants, 251, received BCG vaccine from the Pasteur Institute, but 67 of these soon died from tuberculosis. It turned out that what probably happened was some virulent Mycobacterium tuberculosis had been mixed with the BCG by accident. It was an awful thing that stresses the need for quality control. But it was interesting to see how different people interpreted it in different ways: some that BCG should not be used because of a risk of this kind of thing happening with any live attenuated vaccine (which makes some sense; if you don't have a good way to distinguish between strains, you can't test for contamination); and others (including Calmette) that this just shows that BCG was safe, because it was the fault of some contaminant, not the BCG itself.
But nevertheless, the Britain committee decided at this point that the BCG was still in the experimental phase, not ready for widespread use.
Citation: The Progress of Work on Calmette’s BCG Vaccine. The Lancet 218, 259–261 (1931).
Investigating the research on vaccines, one study at a time.
Saturday, March 29, 2014
Sunday, March 23, 2014
056 - Immunological Studies in Tuberculosis VI. Resistance of Guinea Pigs Vaccinated with Bacillus Calmette-Guérin (BCG)
Today's topic: tuberculosis. This study's authors, Petroff and Steenken, Jr., think that recent (at that time) studies of TB vaccines, especially the BCG live attenuated kind, were too inconsistent and conflicting, possibly because they were done on humans for short periods of time. What they wanted was long-term animal studies. This seems like a controversial opinion, since animals aren't always good models, but they went with it.
Petroff and Steenken Jr. felt that the safety of BCG had already been established, so their goal here was to test its efficacy in preventing tuberculosis, and determine the best dose, route of inoculation, etc.
To do this, they did four experiments with groups of guinea pigs, inoculating them with live BCG or another attenuated strain called R1 or a strain called H37 killed with heat, or nothing (as a control). The inoculations in the first three experiments were either intraperitoneal (in the abdomen) or subcutaneous, and the scientists tested the immune response by seeing if the animals' skin was hypersensitive to TB proteins. Then, after 4-5 weeks, they infected the animals with live, virulent H37 tuberculosis.
Over the course of 516 to 619 days, they looked at the extent of disease among the guinea pigs, as well as average survival time (though this was complicated by some animals dying of other diseases). In terms of extent of disease, it didn't seem like any of the vaccines was especially better than the others, but all seemed to help somewhat (control animals consistently died after 220-230 days, while vaccinated often lived more than 300). R1 might've been slightly better than the others.
The fourth experiment was somewhat different: instead of using adult animals vaccinated by injection, they tested the recommendation of Calmette (the discoverer of BCG) of feeding the vaccine to very young guinea pigs. This didn't work out well; neither BCG nor heat-killed vaccine induced a hypersensitive response, and neither seemed to protect the animals against TB.
Not too great a study, but it shows some effect at least.
Citation: Petroff, S. A. & Steenken, Jr., W. Immunological Studies in Tuberculosis VI. Resistance of Guinea Pigs Vaccinated with Bacillus Calmette-Guérin (BCG). J Immunol 19, 79–92 (1930).
Petroff and Steenken Jr. felt that the safety of BCG had already been established, so their goal here was to test its efficacy in preventing tuberculosis, and determine the best dose, route of inoculation, etc.
To do this, they did four experiments with groups of guinea pigs, inoculating them with live BCG or another attenuated strain called R1 or a strain called H37 killed with heat, or nothing (as a control). The inoculations in the first three experiments were either intraperitoneal (in the abdomen) or subcutaneous, and the scientists tested the immune response by seeing if the animals' skin was hypersensitive to TB proteins. Then, after 4-5 weeks, they infected the animals with live, virulent H37 tuberculosis.
Over the course of 516 to 619 days, they looked at the extent of disease among the guinea pigs, as well as average survival time (though this was complicated by some animals dying of other diseases). In terms of extent of disease, it didn't seem like any of the vaccines was especially better than the others, but all seemed to help somewhat (control animals consistently died after 220-230 days, while vaccinated often lived more than 300). R1 might've been slightly better than the others.
The fourth experiment was somewhat different: instead of using adult animals vaccinated by injection, they tested the recommendation of Calmette (the discoverer of BCG) of feeding the vaccine to very young guinea pigs. This didn't work out well; neither BCG nor heat-killed vaccine induced a hypersensitive response, and neither seemed to protect the animals against TB.
Not too great a study, but it shows some effect at least.
Citation: Petroff, S. A. & Steenken, Jr., W. Immunological Studies in Tuberculosis VI. Resistance of Guinea Pigs Vaccinated with Bacillus Calmette-Guérin (BCG). J Immunol 19, 79–92 (1930).
Saturday, March 15, 2014
055 - Diphtheria—a Preventable Disease
Scroll down if you only care about the epidemiology, the exciting part.
Recap: Diphtheria is a bacterial respiratory disease spread by air or contaminated surfaces/objects. The majority of symptoms, if not all, are caused by diphtheria toxin, a particular protein produced by the bacteria. This means that inactivating the toxin prevents the disease.
This is the basis upon which the practice of treating diphtheria cases with antitoxin came about. Antitoxin, or a solution of antibodies against the toxin, could inactivate it and reduce symptoms when given at the right time. Not good for prevention though. So people were trying to immunize people with combinations of toxin and antitoxin—the toxin to induce an immune response to immunize patients against the toxin, and the antitoxin to prevent the toxin from causing harm. But this was risky.
Then came toxoid: an inactivated form of the toxin that still induced an immune response, more safely. Much better.
So in this report, four Canadian researchers at the School of Hygiene and Connaught Laboratories at the University of Toronto discuss how toxoid vaccination is the first really effective measure in preventing diphtheria in Canada. To quote from the introduction:
But then, in 1925, health workers in Canada decided that toxoid was adequately safe and effective, so Connaught Laboratories started making enough of it to vaccinate many Canadians. Not everyone can tolerate toxoid as well; some have a bad reaction to it, but these can almost always be distinguished using the Moloney test. These people are usually older and have been exposed to diphtheria more in the wild, but aren't always adequately immune despite this, so another dose of dilute toxoid is helpful and safe. Using this test, the risk from immunization was much lower.
The Schick test was often used to determine immune status, but it hadn't been standardized between countries, and different test methods gave different results, so no firm conclusions could be drawn. The authors here recommend another technique: titration of blood antitoxin (i.e. antibody response). I believe this is the technique used today.
They did some tests of immunity with different doses or preparations of toxoid: one to three doses of unmodified toxoid, or 1-2 doses of alum-precipitated toxoid (bound to aluminum as an adjuvant, I believe). They found that three doses of unmodified toxoid, just plain, worked better than alum-precipitated toxoid, in terms of antibody levels induced (titres), and also in terms of how long the antibody titres lasted after immunization (at least 2-3 years, it seemed). At least at first, those receiving three-dose toxoid had higher antibody titres than people who were naturally immune from exposure to diphtheria, though titres decreased over time. The rate of decrease does get slower though, so titres might level out, and re-exposure to diphtheria seem to increase them again.
Epidemiology
Now for the exciting part. They vaccinated 27,000 children in Toronto public schools, and left another 90,000 unvaccinated as controls. Some of the vaccinated had received one dose of toxoid, some two, and some three.
So from the 90,000 controls, they derived expected case rates: how many cases per 10000 or whatever that could be expected given the same exposure. And they found that, compared to these expectations, the actual number of cases they saw in the vaccinated children was always lower. For those who received 1 dose, the number of cases was 29% lower than expected; for two doses, 74% lower, and for three doses, an amazing 90% lower. Only 10% of the children expected to get sick actually did! And these results fit well with the antibody titres observed previously for these dosages.
Then for another 5 years, they brought the number of children vaccinated with 3 doses up to 47,000, and saw similar results: 87 to 97% fewer cases of diphtheria than expected, averaging 91% reduction. Protection did seem to decrease over time since vaccinated, as would be expected from the antibody titre patterns too.
After 1932, though, the amount of diphtheria going around was too low to have a good estimate of protection. The authors credit the toxoid vaccine with this decrease, with reason. Connaught Labs had made 3 million doses of toxoid over 11 years, and it wasn't clear how much of this was used, but it must've changed things a lot. Nothing before had helped this much, even when Canada made antitoxin available for free in 1916 and diagnostic labs had increased and such. The decrease was even greater than would've been expected for the number vaccinated, and the authors attributed this effect to herd immunity.
As an example, the city of Hamilton in Ontario had especially good results. Observe this graph:
Recall that the vaccine had been in increasing distribution starting in 1925. So for 30 years, the cases and deaths had been pretty steady, but then suddenly there was a steep decline with the vaccine. And in Hamilton, they had no deaths since 1930, at least up to this publication in 1938, and no cases since 1933.
Toronto was also doing pretty well; it went from 1640 cases per million in 1930 to 35 per million in 1934, and from around 65 deaths per year in the early 1920s to less than 10 between 1933 and 1937, with zero deaths in two of those years.
Other places in Canada offered free toxoid immunizations to their citizens, such as Brantford, who saw no diphtheria at all between 1931 and 1936. All provinces noticed a decrease in mortality due to widespread vaccination. Seems good.
The last question this paper addressed was that of herd immunity and asymptomatic carriers (those who might be immune enough to not get sick, but could still spread disease to others who were susceptible). Some suggested that many more might be in the latter camp, so spread might not decrease much at all.
However, some people tested a number of people from the population in the early 1920s and 30s, to see how many were positive for the bacteria. If immunization didn't prevent infection, only symptoms, then you would expect that the number of positive tests would be constant even as immunity increased. What they saw, though, was that about 1 in 10 cultures in the 20s was positive for bacteria, whereas very few carriers (fewer than 10) were found anywhere in the 30s, even when thousands of children were tested. So immunity does seem to prevent carrier status also.
Overall: It's difficult to find anything specific to criticize in this data. The differences between vaccinated and unvaccinated are so dramatic; it's pretty obvious that there is some effect. And since the vaccine seems to have been distributed for free by a public institution, at least some of the time, it's not a money question.
Of course, it's not really good enough to stand on its own as proof that the vaccine is worthwhile, I suppose. It's very light on details, like an overview, not going into many methods or diagnostic criteria or anything, or subject selection. In the epidemiology, which might've been like a clinical trial, but we don't know, because it doesn't say how the subjects were selected, or randomized, or if there were a placebo, or any kind of blinding. And they do say that the diagnostic criteria had changed over time, so it's difficult to compare across years. I suppose it's likely that the number of positive diagnoses would've increased with increasing sensitivity, rather than decreasing, but who knows?
So overall, it seems like it fits well into the pattern of research I've been finding up till now, that vaccines work well, but is not so great on its own.
Citation: Fitzgerald, J. G., Fraser, D. T., McKinnon, N. E. & Ross, M. A. Diphtheria—a Preventable Disease. The Lancet 231, 391–397 (1938).
Recap: Diphtheria is a bacterial respiratory disease spread by air or contaminated surfaces/objects. The majority of symptoms, if not all, are caused by diphtheria toxin, a particular protein produced by the bacteria. This means that inactivating the toxin prevents the disease.
This is the basis upon which the practice of treating diphtheria cases with antitoxin came about. Antitoxin, or a solution of antibodies against the toxin, could inactivate it and reduce symptoms when given at the right time. Not good for prevention though. So people were trying to immunize people with combinations of toxin and antitoxin—the toxin to induce an immune response to immunize patients against the toxin, and the antitoxin to prevent the toxin from causing harm. But this was risky.
Then came toxoid: an inactivated form of the toxin that still induced an immune response, more safely. Much better.
So in this report, four Canadian researchers at the School of Hygiene and Connaught Laboratories at the University of Toronto discuss how toxoid vaccination is the first really effective measure in preventing diphtheria in Canada. To quote from the introduction:
"Before the introduction of active immunisation against diphtheria, no substantial reduction in that disease was evident in the Dominion of Canada. Although diphtheria antitoxin was made freely available to practitioners by the public health authorities in almost all parts of the country, for prevention as well as for treatment, the morbidity-rates maintained their previous high levels.
"This is not to say, however, that all efforts at control—isolation of cases and quarantine of contacts, separate of other members of the family, and prophylactic antitoxin—were entirely barren of results. The recorded morbidity-rates of diphtheria are the resultants of different influences in different periods. For example, environmental changes, such as urbanisation of the population, with greater opportunities for human contact, might well have caused a real increase in cases if there had been no control measures; the wider use of laboratory services may have revealed cases otherwise undiagnosed; the use of public health nurses and school nurses may have resulted in more complete notification; and the changing clinical conception of the disease may have included cases of a kind that would not have been included in earlier years. While correction cannot be made accurately for such factors, their possible influence on recorded rates cannot be neglected in making comparisons."Between 1920 and 1924, diphtheria killed between 128 and 232 per million people in Canada, around 1600 deaths a year total. More than 40% of these deaths were in children under 5, and almost 80% in children under 10. Between ages 2 and 14, it was the chief cause of death, 15% of deaths. So, not good.
But then, in 1925, health workers in Canada decided that toxoid was adequately safe and effective, so Connaught Laboratories started making enough of it to vaccinate many Canadians. Not everyone can tolerate toxoid as well; some have a bad reaction to it, but these can almost always be distinguished using the Moloney test. These people are usually older and have been exposed to diphtheria more in the wild, but aren't always adequately immune despite this, so another dose of dilute toxoid is helpful and safe. Using this test, the risk from immunization was much lower.
The Schick test was often used to determine immune status, but it hadn't been standardized between countries, and different test methods gave different results, so no firm conclusions could be drawn. The authors here recommend another technique: titration of blood antitoxin (i.e. antibody response). I believe this is the technique used today.
They did some tests of immunity with different doses or preparations of toxoid: one to three doses of unmodified toxoid, or 1-2 doses of alum-precipitated toxoid (bound to aluminum as an adjuvant, I believe). They found that three doses of unmodified toxoid, just plain, worked better than alum-precipitated toxoid, in terms of antibody levels induced (titres), and also in terms of how long the antibody titres lasted after immunization (at least 2-3 years, it seemed). At least at first, those receiving three-dose toxoid had higher antibody titres than people who were naturally immune from exposure to diphtheria, though titres decreased over time. The rate of decrease does get slower though, so titres might level out, and re-exposure to diphtheria seem to increase them again.
Epidemiology
Now for the exciting part. They vaccinated 27,000 children in Toronto public schools, and left another 90,000 unvaccinated as controls. Some of the vaccinated had received one dose of toxoid, some two, and some three.
So from the 90,000 controls, they derived expected case rates: how many cases per 10000 or whatever that could be expected given the same exposure. And they found that, compared to these expectations, the actual number of cases they saw in the vaccinated children was always lower. For those who received 1 dose, the number of cases was 29% lower than expected; for two doses, 74% lower, and for three doses, an amazing 90% lower. Only 10% of the children expected to get sick actually did! And these results fit well with the antibody titres observed previously for these dosages.
Then for another 5 years, they brought the number of children vaccinated with 3 doses up to 47,000, and saw similar results: 87 to 97% fewer cases of diphtheria than expected, averaging 91% reduction. Protection did seem to decrease over time since vaccinated, as would be expected from the antibody titre patterns too.
After 1932, though, the amount of diphtheria going around was too low to have a good estimate of protection. The authors credit the toxoid vaccine with this decrease, with reason. Connaught Labs had made 3 million doses of toxoid over 11 years, and it wasn't clear how much of this was used, but it must've changed things a lot. Nothing before had helped this much, even when Canada made antitoxin available for free in 1916 and diagnostic labs had increased and such. The decrease was even greater than would've been expected for the number vaccinated, and the authors attributed this effect to herd immunity.
As an example, the city of Hamilton in Ontario had especially good results. Observe this graph:
Recall that the vaccine had been in increasing distribution starting in 1925. So for 30 years, the cases and deaths had been pretty steady, but then suddenly there was a steep decline with the vaccine. And in Hamilton, they had no deaths since 1930, at least up to this publication in 1938, and no cases since 1933.
Toronto was also doing pretty well; it went from 1640 cases per million in 1930 to 35 per million in 1934, and from around 65 deaths per year in the early 1920s to less than 10 between 1933 and 1937, with zero deaths in two of those years.
Other places in Canada offered free toxoid immunizations to their citizens, such as Brantford, who saw no diphtheria at all between 1931 and 1936. All provinces noticed a decrease in mortality due to widespread vaccination. Seems good.
The last question this paper addressed was that of herd immunity and asymptomatic carriers (those who might be immune enough to not get sick, but could still spread disease to others who were susceptible). Some suggested that many more might be in the latter camp, so spread might not decrease much at all.
However, some people tested a number of people from the population in the early 1920s and 30s, to see how many were positive for the bacteria. If immunization didn't prevent infection, only symptoms, then you would expect that the number of positive tests would be constant even as immunity increased. What they saw, though, was that about 1 in 10 cultures in the 20s was positive for bacteria, whereas very few carriers (fewer than 10) were found anywhere in the 30s, even when thousands of children were tested. So immunity does seem to prevent carrier status also.
Overall: It's difficult to find anything specific to criticize in this data. The differences between vaccinated and unvaccinated are so dramatic; it's pretty obvious that there is some effect. And since the vaccine seems to have been distributed for free by a public institution, at least some of the time, it's not a money question.
Of course, it's not really good enough to stand on its own as proof that the vaccine is worthwhile, I suppose. It's very light on details, like an overview, not going into many methods or diagnostic criteria or anything, or subject selection. In the epidemiology, which might've been like a clinical trial, but we don't know, because it doesn't say how the subjects were selected, or randomized, or if there were a placebo, or any kind of blinding. And they do say that the diagnostic criteria had changed over time, so it's difficult to compare across years. I suppose it's likely that the number of positive diagnoses would've increased with increasing sensitivity, rather than decreasing, but who knows?
So overall, it seems like it fits well into the pattern of research I've been finding up till now, that vaccines work well, but is not so great on its own.
Citation: Fitzgerald, J. G., Fraser, D. T., McKinnon, N. E. & Ross, M. A. Diphtheria—a Preventable Disease. The Lancet 231, 391–397 (1938).
Saturday, March 8, 2014
054 - The Effect of Hemophilus influenzae suis Vaccines on Swine Influenza
Richard Shope and others already knew that it was possible to vaccinate against influenza using the influenza virus, in animals at least (049). But an important part of typical swine influenza was an infection with bacteria called H. influenzae suis, which often caused a secondary infectious pneumonia that could be fatal. Immunizing with this bacterium intranasally doesn't prevent the flu, but it seems to help when combined with the virus. It seemed like the bacteria needed help from the virus to get into the body and infect. So Shope wanted to know if it would help on its own when inoculated intramuscularly, into muscle.
So he took H. influenzae suis (henceforth "H.suis" for ease of typing) cultures, killed some of them with heat, and kept the rest alive as a live vaccine. He inoculated 8 pigs with the former, heat-killed ones, and 6 with the live, 3 injections each. He didn't see any side effects from the killed vaccine, but the live consistently caused a fever after the second injection.
After a week or two, Shope tested their immunity with flu virus plus bacteria. He observed them for a few days, and then killed and autopsied them.
All of them got the regular, virus-caused flu, of course. Of those that received the killed vaccine, only one seemed completely protected from the bacterial infection, with no H.suis found anywhere in its body. Another two had bacteria only in their upper respiratory tract, not their lungs, and the remaining 4 had bacteria in the lungs, but their pneumonia was not as severe as that of the 3 unvaccinated control pigs.
The live results were a big weirder. The 6 pigs got very sick when infected with flu, but recovered remarkably after only a day and then had no more than mild illness, compared to controls that had typical flu. All the pigs had bacteria in their respiratory tract, but only one had them in the lungs.
Shope also tested the antibodies in the pigs' serum before infecting them, and none of them had inactivating antibodies against flu or bacteria. Which doesn't necessarily mean they weren't immune.
So in conclusion, intramuscular H.suis, either killed or live, seems to affect the course of the flu but doesn't prevent it. The live seems slightly better at protecting after the initial severe reaction, but the reaction does make it seem less appealing, so it's not clear which is better.
Shope speculates that the severe reaction could be due to an allergic-type reaction to H.suis naturally in the lungs being quickly cleared out, but it's not clear why the killed vaccine wouldn't induce this also.
And he says that this study is just interesting, not practically very useful because there's already a virus-based vaccine that can prevent the whole flu, not just the bacterial part. This is not quite true, as we know, because H. influenzae in humans was a common cause of secondary pneumonia after the flu, so a vaccine against it is quite useful, especially because even today our flu virus vaccine is not super-great enough to depend on.
Citation: Shope, R. E. The Effect of Hemophilus influenzae suis Vaccines on Swine Influenza. J Exp Med 66, 169–175 (1937).
So he took H. influenzae suis (henceforth "H.suis" for ease of typing) cultures, killed some of them with heat, and kept the rest alive as a live vaccine. He inoculated 8 pigs with the former, heat-killed ones, and 6 with the live, 3 injections each. He didn't see any side effects from the killed vaccine, but the live consistently caused a fever after the second injection.
After a week or two, Shope tested their immunity with flu virus plus bacteria. He observed them for a few days, and then killed and autopsied them.
All of them got the regular, virus-caused flu, of course. Of those that received the killed vaccine, only one seemed completely protected from the bacterial infection, with no H.suis found anywhere in its body. Another two had bacteria only in their upper respiratory tract, not their lungs, and the remaining 4 had bacteria in the lungs, but their pneumonia was not as severe as that of the 3 unvaccinated control pigs.
The live results were a big weirder. The 6 pigs got very sick when infected with flu, but recovered remarkably after only a day and then had no more than mild illness, compared to controls that had typical flu. All the pigs had bacteria in their respiratory tract, but only one had them in the lungs.
Shope also tested the antibodies in the pigs' serum before infecting them, and none of them had inactivating antibodies against flu or bacteria. Which doesn't necessarily mean they weren't immune.
So in conclusion, intramuscular H.suis, either killed or live, seems to affect the course of the flu but doesn't prevent it. The live seems slightly better at protecting after the initial severe reaction, but the reaction does make it seem less appealing, so it's not clear which is better.
Shope speculates that the severe reaction could be due to an allergic-type reaction to H.suis naturally in the lungs being quickly cleared out, but it's not clear why the killed vaccine wouldn't induce this also.
And he says that this study is just interesting, not practically very useful because there's already a virus-based vaccine that can prevent the whole flu, not just the bacterial part. This is not quite true, as we know, because H. influenzae in humans was a common cause of secondary pneumonia after the flu, so a vaccine against it is quite useful, especially because even today our flu virus vaccine is not super-great enough to depend on.
Citation: Shope, R. E. The Effect of Hemophilus influenzae suis Vaccines on Swine Influenza. J Exp Med 66, 169–175 (1937).
Friday, March 7, 2014
O469 - Advances in Vaccine Therapy
This isn't a full post, but I really liked this quote (whole section, really) from a review written by Alexander Fleming (who you'll recall is credited with discovering penicillin, not that it's particularly relevant here).
"The question whether or not an individual can be protected against epidemic influenza by means of a vaccine is one which is of the greatest importance in medical practice. This question leads to another, What is epidemic influenza? Before the great war we were quite content to think that it was infection by the influenza bacillus of Pfeiffer, and there is no doubt that in the 1918-19 pandemic this bacillus was present in practically 100 per cent of cases in England and France, and that it was responsible for much of the mortality. However, more recent work, especially at the Medical Research Council laboratires, has definitely established that the primary infective agent in epidemic influenza is a virus. This virus can be passed on in ferrets and mice, and can be cultivated in the incubator in chicken embryos still in the shell. It appears likely that mild influenza, such as the first wave of 1918 or the more recent epidemics, is to all intents and purposes a pure infection of the virus and that the serious and deadly epidemic of 1918-19 was due to a combination of this virus with a bacterium, especially the influenza bacillus.
"A very interesting influenza story comes from America. During and following the 1918 pandemic an epidemic of swine influenza appeared among the pigs in that country. This swine influenza is a serious and fatal disease, and has been investigated by Shope (1937) [054] more thoroughly than was possible in any human disease. Shope discovered that swine influenza was due to a combined infection with a virus and a bacillus practically identical with the influenza bacillus of Pfeiffer. If he infected pigs with a pure virus without the bacillus a transient fever resulted and all the pigs recovered; if he infected them with the bacillus alone practically nothing happened; but if he infected pigs with both the virus and the bacillus typical swine influenza resulted and the pigs died with pneumonia. Shope found that the pigs which had been given the pure virus and had recovered from the trifling infection that resulted were completely immune to fresh infection with the virus. He also found that inoculation of the pigs with vaccines made from the influenza bacillus gave some degree of protection against swine influenza, although it was not so complete as the protection with the virus.
"Here it will be seen that all the animals receiving the vaccine of the influenza bacillus suffered from a much milder disease than the controls, which had not been protected. This observation is of the greatest interest in view of the attempts made to prevent influenza in man with bacterial vaccines, especially those of the influenza bacillus. After the 1918 pandemic many papers appeared stating that such vaccines had conferred a degree of protection against influenza, but none of the figures given have satisfied statisticians. In view, however, of Shope's experimental results with pigs it appears that these claims were justified and that protection can be obtained by such bacterial vaccines.
"Attempts are at present being made to protect man against influenza by means of a vaccine of the influenza virus. The results on experimental animals have been successful, but the opportunity has not yet arisen for the final proof that it can protect man during an epidemic. It seems likely that in the near future it will be possible to obtain a virus vaccine which will give, either alone or in combination with the older bacterial vaccine, complete protection against epidemic influenza in the majority of the inoculated individuals."Citation: Fleming, A. Advances in Vaccine Therapy. Br Med J 2, 99–104 (1939).
Tuesday, March 4, 2014
053 - Minor Points in Diphtheria Immunisation
Previously on the Diphtheria Vaccine Show (or whatever), we saw that toxoid (or inactivated diphtheria toxin) had good potential for immunizing safely, since an immune response against the toxin effectively prevents serious disease. People had been using mixtures of toxin with antitoxin antibodies, but this was risky, so inactivating the toxin just enough that it didn't cause disease but still induced an immune response was better. Also, something called the Moloney test, in which a small amount of toxoid was put under a patient's skin, could detect if an individual was likely to have a severe reaction to toxoid immunization. If so, they could receive a modified dose or something safer, such as a mixture of toxoid and antitoxin serum.
So the current study by H.A. Raeburn examined this question somewhat. He compared results of Schick and Moloney tests for a number of patients. Recall that the Schick test, in which a small amount of intact toxin was placed just under the skin, to see how a patient reacted, was a measure of the patient's immunity: if there was a very positive reaction, the patient was not immune (because they couldn't neutralize the toxin), and if negative, the patient was immune. The Moloney test seemed rather opposite: a positive reaction showed immunity, because the patient's immune system was overreacting to it and causing the reaction. But there was a lot of overlap between the tests, so worth doing both.
Giving a full dose of straight toxoid to a sensitive individual could cause very unpleasant reactions, including headache, vomiting, fever, and overall illness for three days, though recovery was likely I think. So the Moloney test was important, and effective, for avoiding such reactions.
However, mixing toxoid with antitoxin was not risk-free either, since the antitoxin serum often came from horses, so there were other components in it that could induce an immune response. So a person injected more than once with horse serum often developed serum sensitivity, kind of like an allergy probably. And since some diseases at that time, such as scarlet fever, could be treated best only with serum, using up a person's chance at risk-free serum treatment on diphtheria immunization wasn't always the best idea. That is to say, a person could usually count on one serum treatment being okay, the next being more risky, the third even worse, etc. So if possible, it was good to avoid using serum in combination with diphtheria toxoid, because then if the person later needed serum to treat scarlet fever or something, the risk of negative reaction was lower.
Raeburn did a small experiment to test this hypothesis, that toxoid-antitoxin led to higher toxin sensitivity. He tested the serum sensitivity of a number of subjects (using similar methods as with the Schick and Moloney tests), then immunized them either with straight toxoid or toxoid-antitoxin mix, and then tested their serum sensitivity again. Sure enough, more of those immunized with a toxoid-antitoxin mix exhibited serum sensitivity afterwards.
Finally, the best part of this study! Most of the papers I've read about diphtheria toxoid immunization have been focused on whether it could turn Schick-positive (non-immune) patients into Schick-negative (immune); that is, could it effectively induce an immune response? Which is important, but I haven't seen where people correlated this test status to actual immunity by doing epidemiology with diphtheria epidemics or anything like that. Maybe toxoid makes people Schick-negative but for some reason doesn't actually make them immune! Who knows?
But in this study, Raeburn actually does report the effects of a diphtheria outbreak in an immunized population. There were 120 subjects in some sort of house (maybe a hospital or prison or orphanage, it doesn't say), all immunized with toxoid. And there was an outbreak of tonsillitis going around, showing that it was possible and likely that all the subjects were exposed to contagious diseases that spread by droplets through the air, the way diphtheria spreads. But among these 120 vaccinated subjects, only two of them came down with the disease.
This isn't super-great data, since there's no control group, so we have no idea just from this how many we would've expected to catch diphtheria if none of them had been immunized. It seems likely that it'd be more than two, and there's probably some other data from the time period to give some idea, but I don't know where it is. So I'll be on the lookout for better studies in the future.
Citation: Raeburn, H. A. Minor Points in Diphtheria Immunisation. The Lancet 230, 621–623 (1937).
So the current study by H.A. Raeburn examined this question somewhat. He compared results of Schick and Moloney tests for a number of patients. Recall that the Schick test, in which a small amount of intact toxin was placed just under the skin, to see how a patient reacted, was a measure of the patient's immunity: if there was a very positive reaction, the patient was not immune (because they couldn't neutralize the toxin), and if negative, the patient was immune. The Moloney test seemed rather opposite: a positive reaction showed immunity, because the patient's immune system was overreacting to it and causing the reaction. But there was a lot of overlap between the tests, so worth doing both.
Giving a full dose of straight toxoid to a sensitive individual could cause very unpleasant reactions, including headache, vomiting, fever, and overall illness for three days, though recovery was likely I think. So the Moloney test was important, and effective, for avoiding such reactions.
However, mixing toxoid with antitoxin was not risk-free either, since the antitoxin serum often came from horses, so there were other components in it that could induce an immune response. So a person injected more than once with horse serum often developed serum sensitivity, kind of like an allergy probably. And since some diseases at that time, such as scarlet fever, could be treated best only with serum, using up a person's chance at risk-free serum treatment on diphtheria immunization wasn't always the best idea. That is to say, a person could usually count on one serum treatment being okay, the next being more risky, the third even worse, etc. So if possible, it was good to avoid using serum in combination with diphtheria toxoid, because then if the person later needed serum to treat scarlet fever or something, the risk of negative reaction was lower.
Raeburn did a small experiment to test this hypothesis, that toxoid-antitoxin led to higher toxin sensitivity. He tested the serum sensitivity of a number of subjects (using similar methods as with the Schick and Moloney tests), then immunized them either with straight toxoid or toxoid-antitoxin mix, and then tested their serum sensitivity again. Sure enough, more of those immunized with a toxoid-antitoxin mix exhibited serum sensitivity afterwards.
Finally, the best part of this study! Most of the papers I've read about diphtheria toxoid immunization have been focused on whether it could turn Schick-positive (non-immune) patients into Schick-negative (immune); that is, could it effectively induce an immune response? Which is important, but I haven't seen where people correlated this test status to actual immunity by doing epidemiology with diphtheria epidemics or anything like that. Maybe toxoid makes people Schick-negative but for some reason doesn't actually make them immune! Who knows?
But in this study, Raeburn actually does report the effects of a diphtheria outbreak in an immunized population. There were 120 subjects in some sort of house (maybe a hospital or prison or orphanage, it doesn't say), all immunized with toxoid. And there was an outbreak of tonsillitis going around, showing that it was possible and likely that all the subjects were exposed to contagious diseases that spread by droplets through the air, the way diphtheria spreads. But among these 120 vaccinated subjects, only two of them came down with the disease.
This isn't super-great data, since there's no control group, so we have no idea just from this how many we would've expected to catch diphtheria if none of them had been immunized. It seems likely that it'd be more than two, and there's probably some other data from the time period to give some idea, but I don't know where it is. So I'll be on the lookout for better studies in the future.
Citation: Raeburn, H. A. Minor Points in Diphtheria Immunisation. The Lancet 230, 621–623 (1937).
Sunday, March 2, 2014
Historical Aside: An Inquiry Into the Causes and Effects of the Variolæ Vaccinæ, Or Cow-Pox
I found this writing by Edward Jenner recently, and also read it. It's actually sorta fun to read, with much more flowery language than you would find in any scientific or medical publication these days.
Something that makes it a little more interesting is the context of these observations. First, Jenner wrote that he always observed cowpox coming from a disease of horses' heels called "the grease," or from other cows with the pox. But there's a note from the editor in this article saying this hypothesis has since been shown incorrect. So not everything that Jenner observed was accurate.
Secondly, inoculating people with something related to smallpox was not something that Jenner invented. People had been introducing small amounts of smallpox into the skin (what Jenner here refers to as "variolous matter") in order to induce an immune response without a full-blown smallpox infection, for a while before Jenner. It tended to be unpleasant and somewhat risky, but usually preferable than catching smallpox the "natural" way. And if Jenner and other doctors of the time were right, the technique of introducing it into the skin mattered a lot in how safe it was. But what Jenner did contribute was using cowpox instead of smallpox for this inoculation, which was much safer. Henceforth this was called "vaccination," related to the Latin for cow (vacca), and the virus that caused cowpox was later called "vaccinia," though they didn't yet know what kind of thing it was yet.
I know back then there were plenty of negative feelings about vaccination (see here), but it seems like if something similar to what Jenner did were introduced today as an alternative to the modern vaccine schedule, many anti-vaccine people might be much more positively inclined toward it ("natural" immunity, no toxic ingredients, etc), which strikes me as sorta ironic.
"The wolf, disarmed of ferocity, is now pillowed in the lady’s lap. The cat, the little tiger of our island, whose natural home is the forest, is equally domesticated and caressed. The cow, the hog, the sheep, and the horse, are all, for a variety of purposes, brought under his care and dominion."If you've forgotten, Jenner is credited with discovering a vaccine against smallpox, by observing that farm workers who were involved with milking cows sometimes caught a mild disease called cowpox from the cows, and that those who came down with cowpox were thereafter protected from smallpox (a much more serious infection).
"It commonly happens that a disease is communicated to the cows, and from the cows to the dairymaids, which spreads through the farm until the most of the cattle and domestics feel its unpleasant consequences. This disease has obtained the name of the cow-pox.
"Morbid matter of various kinds, when absorbed into the system, may produce effects in some degree similar; but what renders the cow-pox virus so extremely singular is that the person who has been thus affected is forever after secure from the infection of the small-pox; neither exposure to the variolous effluvia, nor the insertion of the matter into the skin, producing this distemper."In this article, Jenner presents a number of cases he has observed in support of this observation, including some children that he intentionally inoculated with cowpox. It's worth a read.
Something that makes it a little more interesting is the context of these observations. First, Jenner wrote that he always observed cowpox coming from a disease of horses' heels called "the grease," or from other cows with the pox. But there's a note from the editor in this article saying this hypothesis has since been shown incorrect. So not everything that Jenner observed was accurate.
Secondly, inoculating people with something related to smallpox was not something that Jenner invented. People had been introducing small amounts of smallpox into the skin (what Jenner here refers to as "variolous matter") in order to induce an immune response without a full-blown smallpox infection, for a while before Jenner. It tended to be unpleasant and somewhat risky, but usually preferable than catching smallpox the "natural" way. And if Jenner and other doctors of the time were right, the technique of introducing it into the skin mattered a lot in how safe it was. But what Jenner did contribute was using cowpox instead of smallpox for this inoculation, which was much safer. Henceforth this was called "vaccination," related to the Latin for cow (vacca), and the virus that caused cowpox was later called "vaccinia," though they didn't yet know what kind of thing it was yet.
I know back then there were plenty of negative feelings about vaccination (see here), but it seems like if something similar to what Jenner did were introduced today as an alternative to the modern vaccine schedule, many anti-vaccine people might be much more positively inclined toward it ("natural" immunity, no toxic ingredients, etc), which strikes me as sorta ironic.
Saturday, March 1, 2014
052 - Vaccination Against Tuberculosis. Comparative Results Obtained with Koch's Bacillen Emulsion, Calmette's B.C.G., and the Caseous Vaccine of the Saranac Laboratory
BCG seems like a good option for vaccinating against tuberculosis, but not everyone was comfortable being injected with live, potentially pathogenic organisms. Especially people in the US and UK. So Hugh Kinghorn and Morris Dworski tried to develop another type of vaccine that was equivalent but more appealing, using killed bacteria.
They based their strategy, as far as I can understand, on the observation that tuberculosis often produces lesions in the lung full of caseous material, which probably also includes products of the pathogen that are harmful to the tissues, so incorporating this material into a vaccine could help protect both against the pathogen itself and its harmful products. They call this the "caseous vaccine."
So then they set off to test this new vaccine in rabbits and guinea pigs. In the first set of experiments, the caseous vaccine did much better than no vaccine at all protecting the animals, and even did better than Robert Koch's attempt to make a TB vaccine. In one group of animals receiving the caseous vaccine, 75% had no disease at all and the other 25% only had mild TB.
In another experiment with just the caseous and negative controls, 35% of the vaccinated had no disease (compared to 26% of the controls), while only 46% of the vaccinated and 74% of the controls had advanced tuberculosis. Kinghorn and Dworski speculated that the controls did so well because their living conditions were good.
Lastly, they compared their caseous vaccine to the BCG version in rabbits. Three groups of 15 animals each got the caseous, the BCG, or none. 89% of those receiving the caseous were protected from TB, compared to 78% from the BCG and 10% from neither. No animals from either vaccinated group had advanced TB, whereas 40% of the controls did. The rest had mild disease.
After about 1.5 years, they re-infected the surviving rabbits from this experiment with TB, to test if the immunity from the vaccines lasted that long. This time, only 17% that got the caseous, 50% that got the BCG, and 20% of the controls had no disease; 17% each of caseous and BCG groups had advanced disease, and 80% of the controls.
They also looked at whether BCG on its own, since it is a live organism, caused disease at all. But they only saw a couple mild lesions on a couple animals, and no other symptoms.
So it seemed like the caseous worked pretty well at first, but didn't last very long compared to the BCG. And neither is super-great, so the authors recommend not relying on the vaccine as the only preventative measure, which seems wise.
From this study, the caseous vaccine does seem potentially useful especially for people who are nervous about attenuated vaccines, but no future papers have cited this study and I've never heard of caseous vaccines, so it might be only a historical curiosity at this point. There's some pretty good animal data about the BCG here though.
Citation: Kinghorn, H. M. & Dworski, M. Vaccination Against Tuberculosis. Comparative Results Obtained with Koch’s Bacillen Emulsion, Calmette’s B.C.G., and the Caseous Vaccine of the Saranac Laboratory. Trans Am Clin Climatol Assoc 53, 1–14 (1937).
They based their strategy, as far as I can understand, on the observation that tuberculosis often produces lesions in the lung full of caseous material, which probably also includes products of the pathogen that are harmful to the tissues, so incorporating this material into a vaccine could help protect both against the pathogen itself and its harmful products. They call this the "caseous vaccine."
So then they set off to test this new vaccine in rabbits and guinea pigs. In the first set of experiments, the caseous vaccine did much better than no vaccine at all protecting the animals, and even did better than Robert Koch's attempt to make a TB vaccine. In one group of animals receiving the caseous vaccine, 75% had no disease at all and the other 25% only had mild TB.
In another experiment with just the caseous and negative controls, 35% of the vaccinated had no disease (compared to 26% of the controls), while only 46% of the vaccinated and 74% of the controls had advanced tuberculosis. Kinghorn and Dworski speculated that the controls did so well because their living conditions were good.
Lastly, they compared their caseous vaccine to the BCG version in rabbits. Three groups of 15 animals each got the caseous, the BCG, or none. 89% of those receiving the caseous were protected from TB, compared to 78% from the BCG and 10% from neither. No animals from either vaccinated group had advanced TB, whereas 40% of the controls did. The rest had mild disease.
After about 1.5 years, they re-infected the surviving rabbits from this experiment with TB, to test if the immunity from the vaccines lasted that long. This time, only 17% that got the caseous, 50% that got the BCG, and 20% of the controls had no disease; 17% each of caseous and BCG groups had advanced disease, and 80% of the controls.
They also looked at whether BCG on its own, since it is a live organism, caused disease at all. But they only saw a couple mild lesions on a couple animals, and no other symptoms.
So it seemed like the caseous worked pretty well at first, but didn't last very long compared to the BCG. And neither is super-great, so the authors recommend not relying on the vaccine as the only preventative measure, which seems wise.
From this study, the caseous vaccine does seem potentially useful especially for people who are nervous about attenuated vaccines, but no future papers have cited this study and I've never heard of caseous vaccines, so it might be only a historical curiosity at this point. There's some pretty good animal data about the BCG here though.
Citation: Kinghorn, H. M. & Dworski, M. Vaccination Against Tuberculosis. Comparative Results Obtained with Koch’s Bacillen Emulsion, Calmette’s B.C.G., and the Caseous Vaccine of the Saranac Laboratory. Trans Am Clin Climatol Assoc 53, 1–14 (1937).
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