Covid rebound isn’t rare, and Paxlovid remains the lead suspect.
On the asymmetry of anecdotes and the race for data.
First Lady Jill Biden has Covid rebound. After testing positive on Monday, August 15th, Mrs. Biden tested negative on rapid antigen tests on Sunday, indicating that she was no longer contagious, but tested positive again, on Wednesday, August 24th. So far, she is symptom-free during her relapse.
When President Biden experienced Covid rebound last month (with worsening symptoms), the administration said that this was “rare.”
The ship has sailed, folks. Covid-19 rebound is not rare. Both the President and the First Lady had Covid rebound. Both took Paxlovid. The odds of this being rare, but just “bad luck,” are vanishingly small.
The question is whether Paxlovid, Pfizer’s antiviral medication proven to lower hospitalizations and death among unvaccinated patients at high risk of developing severe Covid-19, is responsible.
At the time of President Biden’s rebound case, I pointed out to an administration official that both Dr. Tony Fauci and President Biden had taken Paxlovid and experienced rebound. If the next 18 administration officials who took Paxlovid didn’t have rebound, I told the official, we could maybe say that the rebound rate was 10% (2/20=10%). Of course, I believed the rate was far higher than 10%, let alone the, 1-2% that Pfizer reported in its clinical trial (regardless of whether participants had taken the drug or placebo).
Why did I think rebound was much more common? The lowest form of medical evidence: anecdotes. I had simply known too many people who had taken Paxlovid and had experienced rebound. While those anecdotes certainly were not enough to warrant a strongly-held belief, I began to feel more attached to the idea, due to the asymmetry of anecdotes.
Here’s how that works. Imagine that a side effect like Covid rebound happens a little over 2% of the time. If I knew 25 people who had taken Paxlovid, the odds that none of them would have experienced rebound would have been around 60%. So, if none of the 25 Paxlovid-takers I knew had rebound, I might think "Well, I know a bunch of people who took it, and nobody I know has had this complication. It must be extremely rare.” The flaw in that logic is that I would be assuming that almost nobody was having the complication. But assuming the 2% figure, if I had sought out 50 people who had taken Paxlovid, the likelihood of rebound occurring in at least one of them would have been around 64%.
Now, if I had randomly heard about one case of Paxlovid rebound, I might have ignored it. After all, I know hundreds of people who would go out of their way to tell me if they had experienced any complications or side effects to any drug. So, I could have heard of one case and thought, “Well, okay, that’s one person among the hundreds of people in my social network.” But when I started to get texts and emails from many people who were having rebound—not to mention learning about Dr. Fauci and President Biden’s cases—the asymmetry of anecdote became impossible to ignore. For Paxlovid rebound to be rare in my network, I’d have to find dozens of people who had recently gotten Covid and taken Paxlovid, but not had rebound. Those folks were not materializing.
Just the fact that President Biden and Dr. Fauci had Covid rebound was striking to me. It could not be chalked up to sampling of an unusually high-risk population. That kind of thing can happen in some situations. For example, the fatality rate of Covid-19 might be 10%, if you sampled cases from an intensive care unit. But if you zoomed out and measured the fatality rate in the whole hospital, the fatality rate would appear to drop vastly, say to 1%. And if you zoomed out to the entire ZIP code where the hospital is located, the fatality rate would drop further still. There was no special reason to think that President Biden and Dr. Fauci represented some high-risk group that didn’t reflect the general population in their age group. If anything, they had the advantage of frequent testing, which most of the public does not. This meant that if we zoomed out and tested everyone as often as Biden and Fauci got tested, we’d probably start to find the same thing.
A body of medical evidence is beginning to emerge, suggesting that this is exactly what’s happening, and that President Biden, Mrs. Biden, and Dr. Fauci do represent a reasonable cross-section of the older population.
In my next post, I’ll provide answers to frequently asked questions about Covid rebound/Paxlovid rebound.
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