068 - Fatality Rates of Small-Pox in the Vaccinated and Unvaccinated

This is more a series of studies than a single one, all with the same title. A sort of discussion between physicians, regarding the value of vaccination against smallpox.

It started with a letter in the British Medical Journal from R.P. Garrow, which presented some data over 4 years of deaths from smallpox in Britain, comparing vaccinated and unvaccinated cases.¹ As Garrow says, it should be expected (assuming vaccination is helpful) that there be more deaths among unvaccinated than among vaccinated, but in these data the case-fatality rates (proportion of people with the disease who died from it) was higher among the vaccinated, 30 in 10000 vs. 6 in 10000. The number of cases of smallpox is higher in the unvaccinated (almost 7000 vs. 4000 in vaccinated), but we don’t know what proportion of these populations these numbers represent. All these cases are in subjects over 15 years old. Garrow remarks that the cause of death may sometimes be questionable, and this might explain the discrepancy, but he’s not sure.

This letter is followed by another collection of letters from other physicians, in the same journal.² First, Dr. Percy Stocks tries to explain the strange data by pointing out that the age distributions of the two groups are pretty different. Check out the number of cases:

It appears there are a lot more cases in unvaccinated in general, though again the proportion is unknown, but most of the cases are in the young, decreasing with age. Compared with this is the vaccinated population, where the median age seems to be around 40-50 years. Similar results are seen with the number of deaths from smallpox by agegroup:

 This seems to indicate a limited duration of immunity from vaccination, such that those vaccinated as children are no longer as well-protected as they used to be, and thus get sick again in old age. And the number of deaths in any group is so small that it’s hard to compare the groups.

Dr. Fred Wynne repeats the explanation of waning immunity in his letter, though I’m not sure why this makes everything okay. He also admonishes Dr. Garrow for giving support to antivaccinationist arguments, which apparently was a problem even then.

Dr. C. Killick Millard points out that smallpox comes in two forms: variola major, the serious, deadly form, and variola minor (AKA alastrim), which is much milder. Cases of the latter are much more common, but Dr. Garrow didn’t distinguish between the two, so it’s hard to say what exactly is going on. Thousands of minor cases with a few major ones just makes for a complicated situation.

Finally, L.A. Parry comes in with a bunch more questions, about how supposedly less vaccination means fewer deaths and cases from smallpox, etc, without providing reference to any such data, prompting the BMJ editor to admonish Parry for introducing “assumptions of fact into framework of his questions.”

I tried to figure out who this Parry guy is, but everything else he published (judging by titles, at least) didn’t seem that different from what I would expect from a typical medical doctor. Weird.

In the third letter, this one in the Lancet, Dr. Duncan Forbes provides more data from the early 1900s in Britain.³ This data is purely serious smallpox, variola major, as far as he knew, excluding all variola minor. The number of cases was much smaller, about 500 total, but the case-fatality rates are very different. For the unvaccinated, 19.2% who caught the disease died (10 of 52), vs. 1.9% of the well-vaccinated (more than one vaccination scar) (7 of 362). In between were those who were said to be vaccinated but had no scar, or had only one scar: with no scars, the rate was 17.1%; with one scar, 10.8% (combined 13%). From this, Dr. Forbes points out the importance of good vaccination.

Finally, Stallybrass wrote to the Lancet to point out differences in smallpox between northern and southern Britain.⁴ Apparently many people in the north were unvaccinated, and variola minor (the mild kind) was rampant there, but in the south, where most people were vaccinated, variola major occasionally came in from visitors from France or Spain. Stallybrass tracked down all the deaths from smallpox and discovered that among the vaccinated, almost all deaths were in the south in people over 30, whereas almost all deaths in unvaccinated were in the north in people under 15. Overall, case-fatality rates were lower for vaccinated (10 in 10000 compared to 11.2 in 10000), and lower in age groups under 15 and over 30. In the middle, there was just one death in either group, so it’s hard to compare; could be just due to chance.

He also points out that older people may be more susceptible to smallpox, especially the worse version in the south, and indeed most deaths in the vaccinated are in the south in older people. In contrast, even the mild version is dangerous for the very young when unvaccinated.

Summary

It’s tricky to say what’s really going on exactly with these data. What it does show is how a complicated question like this can be confused more and more by a lack of details. It’s all too easy to distort the data to show what you want to show, if you have an agenda, simply by leaving out certain details, like age or geographical distributions.

Citations:

1.  Garrow, R. P. Fatality Rates of Small-Pox in the Vaccinated and Unvaccinated. British Medical Journal 1, 74–74 (1928).

2.  Stocks, P., Wynne, F. E., Millard, C. K. & Parry, L. A. Fatality Rates of Small-Pox in the Vaccinated and Unvaccinated. British Medical Journal 1, 115 (1928).

3.  Forbes, D. Fatality-Rates of Small-Pox in the Vaccinated and Unvaccinated. The Lancet 211, 208 (1928).

4.  Stallybrass, C. O. Fatality-Rates of Small-Pox in the Vaccinated and Unvaccinated. The Lancet 211, 313–314 (1928).