Light at the end of the tunnel
We all had to have been encouraged by the big announcements from Pfizer and Moderna this week. Both companies announced that their Phase 3 vaccine trials have shown surprising positive results! Both vaccines are more than 90% effective in their trials and neither has caused significant or harmful side effects. Both vaccines appear to prevent COVID 19 and serious disease even when they are not effective in preventing infection.
WOW!This is just the good news we need when COVID 19 is rampant across the world in a third more ominous wave and Governor Inslee has asked us to once again restrict our activity in the interest of public health. But (since we all have more time on our hands) I had to ask myself: what does all that news mean? Who got tested and how are vaccines evaluated?
So I did a little research. Thank you Wikipedia and Google!
Vaccine Efficacy is the percentage reduction of disease in a vaccinated group of people compared to an unvaccinated group, using the most favorable conditions. Vaccine efficacy was designed and calculated by Greenwood and Yule in 1915 for the cholera and typhoid vaccines. It is best measured using double-blind, randomized, clinical controlled trials, such that it is studied under “best case scenarios.”
It is calculated as VE = (infection rate of control group - vaccinated group)/ control group.
Not too complicated.
About 44,000 people participated in the Pfizer vaccine trial - 22,000 got the vaccine and 22,000 got a placebo. As of this morning, 170 people subsequently contracted COVID 19. Of these, 162 were from the control group and 8 got the vaccine. Here is the math:
VE = (162 - 8) / 162 = 95.06%
Statistically, Pfizer needed to wait until more than 162 people became infected with COVID to have 90% confidence in the results. That was announced this morning. The statistics and results for the Moderna vaccine are similar. Both appear wonderful. BTW, flu vaccine efficacy is around 60-70%.
So there you go! We can confidently see a light at the end of the tunnel. But we still need to walk through the tunnel to reach the light. Please take care, stay safe and have a virtual Thanksgiving this year.
Comments