Pfizer originally said the Paxlovid rebound rate (the percent of people who test positive for COVID again after finishing the Paxlovid antiviral course) was about 2%. However, as new variants emerged, Paxlovid rebound became more common. The CDC put out an advisory about it in May, but didn't propose effective ways to address it. Doctor friends recently estimated Paxlovid rebound rates to be more like 20%-50% based on what they were seeing in their patients. Many people with some medical knowledge now believe that the default Paxlovid course of 5 days is too short for many patients, and the result is something similar to what happens if you stop a course of antibiotics too soon. This has now been backed up by studies from reputable academic institutions (eg the UCSD one from June). It's now common knowledge among my friend group that it's worth getting an extra few days of Paxlovid to really crush the infection. Pfizer even put out a press release saying "If you get Paxlovid rebound, take a second course of it". However, the FDA and most doctors still don't advise this. I'm not sure why; maybe it has to do with a fixed government budget for buying Paxlovid for Americans? Apparently even the president's doctor doesn't advise this, so Biden got Paxlovid rebound. I'd like to think that if I were the president, I'd have a team of physicians ready to think bold out-of-the-box thoughts and make conscious bets on emerging data.
But somehow my group of friends seems to have better access to medical knowledge than the president, at least in this instance. Maybe there are other factors I'm not considering; maybe Biden's kidneys were close to the limit of what's contraindicated for Paxlovid.
I realize the FDA is being conservative and careful, and wants to make sure that its recommendations don't accidentally give millions of people liver or kidney problems. It's a tough job. However, it seems like there's been plenty of time from when I first heard that there's a lot of paxlovid rebound (maybe 2-3 months ago) and now. The virus is evolving quickly, and our institutions need to be nimble. It should be possible to run a study of this sort and get a full bureaucratic buy-in to the result and consequent policy decisions in under 2 months.