Thread by @katherineefoley

One thing I don't see anyone talking about in the @pfizer #CovidVaccine discussion is the difference between efficacy and effectiveness. It's a small nuance, but it matters when we're talking about how to end the pandemic. A short thread: 1/x qz.com/1930285/

2/x We got the news* yesterday that Pfizer's vaccine candidate seemed "90% effective." If we're going by the @CDCgov's definition, the company really meant "efficacy."

*It's from a press release. We want independent, peer-reviewed, published data before we make any conclusions

3/x "Efficacy" means a vaccine seemed to work at preventing illness in a randomized controlled trial. These trials are the gold-standard of scientific data, but they're also not reflective of the real world.
cdc.gov/csels/dsepd/ss…

4/x This is bc trials are still concerned about safety; they generally feature healthier people with minimal pre-existing conditions; they also give doses of vaccine or placebo exactly on schedule. It's a perfect-case scenario, in other words.

5/x We should be much more concerned with Pfizer's vaccine *effectiveness,* which is based on observational data collected after real-world uptake. This means more diverse populations, older populations, sicker populations, and folks who don't get the perfect dosage timing.

6/x Pfizer said that they had 30% diverse pop in US trial and 42% diverse pop in global trials. We don't know what that actually means—and it's important bc Black and brown folks have been disproportionately burdened with more severe cases of #COVID19

7/8 On top of that, we have no data on how long it takes to generate immunity, how long immunity lasts, or whether the vaccine can reduce the severity of the illness. All that stuff we'll have to figure out in its effectiveness later on.

8/8 So TL;DR, it is HIGHLY unlikely that if Pfizer's vaccine gets an EUA from the FDA, it'll straight up protect 9/10 people who get both doses. BUT there's another reason to be excited about this vaccine...which I'll be sharing shortly ✨ qz.com/1930285/what-d…