019 - The Use of a Vaccine in the recent Epidemic of Influenza

Another interesting thing that was going on in 1918 is something you might have heard of: the worst influenza pandemic in recorded history, sometimes called Spanish flu, which killed up to 100 million people (~5% of the world’s population) in all parts of the world.³

It doesn't seem like the influenza virus had been discovered at the time, not until the 30s, but it did seem like health officials at the time understood that the nature of the disease was not bacterial. Nevertheless, they recognized that a bacterial respiratory infection and pneumonia often accompanied cases of influenza, and that such an infection was responsible for much of the mortality associated with flu.

So today’s study describes the arrival of 1918 flu in Winnipeg, Canada in October of 1918, and the attempt to create a vaccine against the bacteria that caused secondary pneumonia in patients.¹

After swabbing and sampling more than 100 cases, they determined which bacteria seemed most closely associated with the disease: some kinds of streptococcus, pneumococcus, and something called “Bacillus influenzae.” So they made a vaccine in the typical way at the time: grow these up, kill them with tricresol and heat, and inject people.

Then they inoculated soldiers in Winnipeg, 4842 of the 7600 present, leaving 2578 unvaccinated.

Of the vaccinated, about 6% were hospitalized with flu, 0.35% got pneumonia, and 0.1% died. Though of the 5 deaths, 3 had only been vaccinated after being admitted to the hospital, and the other two had been vaccinated 3 or 10 days before, so it might've been too late for them anyway.

Of the unvaccinated, about 9% were hospitalized with flu, 1.5% got pneumonia, and 0.62% died. The average hospital stay of the unvaccinated was twice as long as the vaccinated, and the captain of the soldiers said it seemed like the unvaccinated had more severe cases.

So that’s a 33% reduction in flu, 77% reduction in pneumonia, and 84% (or probably more) reduction in deaths from vaccination.

It seemed like the populations were mostly equivalent in exposure, except for some of the flu cases being from troops coming in on trains, rather than being in the camp, so that complicates things a bit.

Then there was another experiment, this time with civilians: 52,999 were vaccinated and another 85,941 not. About half who were received one dose, while the rest received two.

Number of doses didn’t affect number of flu cases much (9.7% for 2 vs. 9.8% for 1), but pneumonia cases decreased 18% and deaths 57%. Not super impressive.

But compared to unvaccinated, there seemed to be up to 61% reduction in flu cases, 77% in pneumonia, and 86% in deaths. And of doctors surveyed, 93% said the vaccine seemed to have an effect, and 86% said it seemed to help prevent fatalities in pregnant women. However, precautions were not taken to make sure these populations were equivalent, and the types of bacteria infecting people seemed to vary between different places and/or times, so it’s not a very good study overall.

"Contemporary medical opinion generally agreed that while the right vaccine would be invaluable, it probably had not been found yet...the consensus was that vaccine should only be used on an experimental basis, its results being unknown and perhaps dangerous."²

References:

1. Cadham, F. T. The Use of a Vaccine in the recent Epidemic of Influenza. Can. Med. Assoc. J. 9, 519–527 (1919).

2. McGinnis, J. P. D. The Impact of Epidemic Influenza: Canada, 1918-1919. Hist. Pap. 12, 120 (1977).

3. Wikipedia.