This touches on a question I had. Out of the tens of thousands of people vaccinated in countries where COVID runs rampant, how were there only 90ish people in the control group? I would have expected thousands.
Both groups have (approximately) the same size, in the tens of thousands. The first evaluation is done when 90 or so cases have been confirmed, not knowing which group they belong to. The blinding of these subjects is then unsealed, in this case revealing that 90 of the 95 confirmed infections occurred in the control group. This distribution means the vaccine has been highly effective at preventing infection.
Sorry, I meant just 90 people infected (obviously the vaccine arm has much fewer), but after running the numbers that's actually about right for the prevalence rate we see in the US.
This isn't the final evaluation. There will be another at ~150 cases. The numbers may seem small, but this is enough for the purpose of deciding for or against approval. Anything over 80% effectiveness would likely be approved, so it doesn't matter whether the true value (insofar one exists) is 90%, 95%, or something in between. It's useful regardless.
Oh, I didn't know that, thanks. I'm sure it's enough for statistical significance given the difference, I was just wondering why there were so few cases in 30k people, but it looks like that's just the normal case rate.
Thousands (30) of people are in the trial, half were assigned randomly to the control group. So far 95 people in the trial have caught COVID and, when they unblinded the data, they discovered that 90 of those infections where in the control group. Since participants were randomly assigned into the test group vs the control group and so both groups should have the same amount of exposure, this is a strong signal that the vaccine was effective. Here's an article about Moderna's trial with a link to their 135 page (!) design doc https://www.livescience.com/moderna-vaccine-trial-protocol.h...
