Brief explanation of the difference between methods of the ICL/REACT study and the many longitudinal studies I have cited before. These studies below, including ours, followed individuals over time to quantify antibody levels and decay
The ICL work is a yes/no population study to check the frequency of people with antibodies. For these types of tests, a strict cutoff is used to minimize the number of false positives (telling someone they have antibodies when they don't). This comes at a cost of telling...
some people they don't have antibodies when they do. Lesser of two evils. But for this reason, seroprevalence studies aren't ideal for quantifying the duration
of antibody production. Consider the graph below of a stereotypical antibody response, with range of outcomes in gray Image
Early in the pandemic, when people are near the peak of antibodies, false negatives are infrequent b/c it is far from the cutoff. Later, the nadir is closer the cutoff and you would expect more false negatives even though the response is normal and people do still have Abs.
Now the question is whether that nadir of Abs is protective. I think so, and I will explain why this low bar bodes very well for vaccines in a later thread. But for now, IMO, the decrease in seroprevalence in the REACT study is exactly what you would expect in a normal response.

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More from @deeptabhattacha

1 Nov
I received this email from someone last week that I can't stop thinking about. I probably received this since I have been openly optimistic about vaccine efforts. So I wanted to explain exactly why I am glass half-full.
Many of the grim posts about predicted efficacy (only 50%) have used the flu vaccine as a comparison. But as with many aspects of the pandemic (e.g. IFR, transmission), flu is not a very informative prior for vaccines without some major adjustments.
To be considered effective, the flu vaccine has to protect against symptomatic disease by *any* flu strain, whether it is in the vaccine or not. There are usually at least 4 circulating flu strains and sometimes the vaccine doesn't match one or more strains. That's a big ask...
Read 11 tweets
31 Aug
I've been reading the discussion on re-infection events, with some now arguing that this is not rare. This is being interpreted at the extremes that protective immunity is not possible. In this thread, I am going to argue that re-infections are rare based on data so far.
First, let's look at our toolbox on how re-infections can be measured w/o sequencing everyone. This Herculean paper on common coronas medrxiv.org/content/10.110… uses Ab responses as surrogates for re-infection. You will see that in the top row, there are periodic spikes in Abs... Image
This means that a person has been productively infected by a same or similar virus, and the immune system revs up again with new Abs. Keep in mind that these data are for common cold-causing coronaviruses, not SARS-CoV-2. However, we now have a dozen+ reports on serology...
Read 9 tweets

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