This is the kind of insight that I like to see: balanced viewpoint, and realistic about the limitations of studies. Regardless of the counfounding factors, it’s hard to argue with the massive risk reduction enjoyed by those previously infected by COVID.
24 April 2021, emphasis added
Antibodies are a “surrogate” marker. We think they might tell us something useful, but we can’t really be sure... we still don’t really know whether antibodies play a meaningful role in fighting covid or not. Correlation isn’t always causation. Antibodies appear to be a good marker for prior infection, but that doesn’t mean that they have a causal role in preventing a re-infection.
So, what we really need is a study that looks at the degree to which people actually get re-infected, not more studies that look at antibodies. Once we have that, we can do a comparison with the results of the vaccine trials, and then we will finally have a reasonably good estimate of whether prior infection or vaccination provides a higher level of immunity, or if they are equivalent. That is now exactly what we have, thanks to a study that was recently published in The Lancet.
So, on the face of it, prior infection is equivalent to the Pfizer and Moderna vaccines in terms of the level of protection offered, and much better than the Astra-Zeneca vaccine and J&J vaccine. In light of this, it seems completely unnecessary for people who have had COVID to get the vaccine. In fact, if the goal of governments is to get their populations to herd immunity as quickly as possible, it would make more sense to tell people who have had confirmed COVID-19 that they don’t need to get vaccinated. Vaccinating people who have already had COVID-19 means delaying vaccination of people who haven’t had it, which means delaying the onset of herd immunity.
There is one potential problem with taking the 92% number at face value, especially in relation to the results from the vaccine trials, and that is that this is an observational study, not a randomized trial, so there is significant scope for confounding...
The researchers attempted to correct for confounders to the extent that they were able, and came up with a modified risk reduction of 93%. But correcting for confounding is really a kind of guessing game. It isn’t a very reliable technique. And for all the confounders that are known and that can be corrected for, there are plenty more that aren’t known and can’t be corrected for.
WIND: one concern: I don’t understand how the false positive PCR test confounder is accounted for. But the results are so compelling that some degree of error is not likely to matter.
BTW, if antibodies are not shown to play a causal role in preventing re-infection, what does that say about vaccines whose efficacy is judged by antibody levels?
Also, it is not an established medical fact that a positive PCR test is actually a COVID infection.
Finally, it seems sketchy at best to assume that a vaccine could deliver the full in-vivo physiological response that an actual infection does. Time (years) will be needed to study that question.