I always enjoy reading Jay Wiener’s columns and April 15th was no exception. I, like Mr. Weiner, am strongly supportive of mass COVID vaccinations and have been vaccinated myself. However, I would like to clarify and correct his statement that the “[the vaccines] are ….95% effective. And that 5% (of the vaccinated) can contract and transmit the disease.”
This is a common misunderstanding of how vaccine effectiveness is measured. In the Pfizer vaccine trial published in The New England Journal of Medicine on Dec.31, 2020 (NEJM 2020. 388:2603-2615), 21,728 people received placebo and 162 or 0.7 % of them developed COVID. Of the 21,720 people in the vaccine group, eight or 0.04% developed COVID. This means the vaccine prevented 154 cases of COVID and was therefore 95% effective in preventing disease (154/168). Since only eight people who were vaccinated got COVID, only one in 2,716 vaccinated people could “contract and transmit the disease,” not one in 20 as suggested by Mr. Wiener. Of course, this same data points out that only one in 134 unvaccinated people can contract and transmit the disease. These findings mean that 141 vaccinations must be given to prevent one case of COVID and that 2,414 must be given to prevent one severe case.
These numbers will change some since the observation period for this initial study was only five months, but what does all this mean? Well, it looks like the susceptibility of the general population to COVID is low, and that the susceptibility of the vaccinated population is extremely low. So, by all means get vaccinated as soon as possible, but don’t forget to keep it in perspective and live your life.
William D. Frazier, M.D.