Vaccine data in kids

The external scientific advisory committee for the FDA meets next week to consider the Pfizer Covid vaccine in kids 5-12.  Pfizer’s briefing to the committee is now up on the website; the FDA briefing is not (as of midday Saturday).

Demographically, the trial isn’t as representative as the initial adult trials, which were much better than usual. About 10% of the participants had asthma and about 10% were obese. Black and Hispanic populations were under-represented by about a half relative to the US population —  though there has been no indication that race/ethnicity matters for vaccine efficacy so far.

For the extension to ages 5-12 there are basically three questions

1. Is the dose right? They used 1/3 of the adult dose. Using too much would increase  adverse effects; using too little would not provide reliable immunity
2. Is there anything new and worrying about adverse effects? This trial, like all randomised trials, is too small to see surprising and rare adverse reactions that happen to 1 person in 10,000 or 1 in a million. These can only ever be picked up by post-marketing surveillance, as we’ve seen for both the Pfizer and AstraZeneca vaccines. Safety signals in the trial would involve milder, less rare reactions at elevated rates.
3. What is the risk/benefit relationship like, given the relatively lower risk from Covid in kids and the fact that (in contrast to many infectious diseases) kids don’t seem to spread it more effectively than adults do?

The data are positive on the first point. Pain and redness at the injection site are a bit more common than with teenagers given the full dose; systemic reactions such as fatigue and fever are a bit less common.  Levels of neutralising antibodies are about the same as in teenagers given the full dose.

On the second point, the trial is again positive. Nothing new seems to have been seen (though this is where the FDA briefing will be important, to see if they agree — how you classify adverse events can make a difference).

It’s harder to say what regulators will think for the third point, but if the FDA were willing in principle to approve based on a trial of this general design there doesn’t seem to be anything obvious in the results that would make them not approve based on these data.

Update: FDA’s briefing is now available.  The main new information is an explicit risk-benefit analysis. As you’d expect, the net benefit depends on the Covid incidence, but they say the net benefit might be positive even under the lowest-incidence case (and that’s assuming only 80% effectiveness against hospitalisation, which is probably a bit low, and a pessimistic view of the data on myocarditis). They don’t seem to model any community effect of vaccination by reducing infection in other people and thus reducing exposure to the virus. Risk-benefit is where the most interesting discussion should be at next week’s meeting.