what about the MRNA covid vaccines?

The mRNA COVID vaccines were tested in placebo-controlled randomized trials, but the evidence you have stops in 2023 and leaves critical questions unanswered.

The Pfizer and Moderna trials each enrolled over 30,000 adults and compared the vaccine to a placebo injection [1, 2, 3]. Both showed very high efficacy against symptomatic COVID-19 in the short term. The Pfizer trial reported 95% efficacy, with 8 cases in the vaccine group versus 162 in the placebo group [6]. The Moderna trial reported 94.1% efficacy [3]. Both were funded by the manufacturers.

The adverse event rate was about double the placebo rate for both vaccines [1]. That means roughly twice as many vaccinated people reported a reaction compared to those who got a placebo shot. The trials followed participants for a median of about two months before the placebo groups were offered the vaccine, so long-term safety data beyond that window comes from observational studies, not from the original randomized comparison.

What the evidence here does not cover: how efficacy held up against later variants, whether the vaccines prevented death in healthy young adults (the trials enrolled mostly healthy people and had very few deaths), and what the all-cause mortality difference was between vaccinated and unvaccinated over years. Those questions require studies that compared vaccinated to unvaccinated over time, not just the short placebo-controlled trials. The evidence you retrieved does not include that comparison.

My call: the mRNA vaccines clearly prevent symptomatic COVID in the short term in placebo-controlled trials, but the evidence here does not answer whether they reduce all-cause mortality in healthy people or what the long-term net benefit is. Confidence: moderate for short-term efficacy, low for long-term net benefit.