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Ok, took me a few days to properly process the stunning results of the Delhi serosurvey. Unfortunately we only have a press conference with a few slides telling us that 22.86% of 20,000 people sampled tested positive for antibodies to Sars-cov2: timesofindia.indiatimes.com/india/almost-1…
This was done from June 27 to July 10 and they did a randomised sampling of every nth household and also sampled minors, they used the Kavach ELISA developed by ICMR (sens 92.3 and spec 97.9). The results were only recently released in the July 21st PC.
So why r these results stunning? Well, for one they imply 46 lakh infections, whereas the official count is only 1.2 lakh to date. Meaning only 1 in 38 were actually detected by antigen testing! Either implies pathetic testing or huge percentage of asymptomatics?
While wide variance has been noted for these reasons in other serosurveys, the Delhi seroprevalence is especially high. Most studies are btw 5 and 15% (higher in dense urban) Even NY which was harder hit has a lower seroprevalence!
ft.com/content/4e4dda…
Why is this important? Coz it implies the disease is much more infectious and much less lethal. How do we derive this? Naturally as deaths due to covid are more or less (LESS in CAPS!) reported, the true infection fatality (IFR) has a much larger denominator (total infections)
So media has been reporting IFRs ranging from 0.03 to 0.07. But most experts believe it can't be lower than 0.2 and she be around 0.6-0.7 based on other countries data.. refer
So why such a huge discrepancy? Even if we account for underreported deaths it's still nearly 10x lower than Western data! Were we wrong all along? Is it really just a bad flu? @anupampom has 1 explanation: a young popul means our IFR will naturally b low
But even accounting for this the IFR seems be at least half of what one might expect!
So what can explain this? The are a lot of theories, some more far fetched than others but consider this: I first read about this interesting finding last week. 2 patients of covid in Singapore had false positive tests to Dengue IgG and IgM:
ncbi.nlm.nih.gov/pmc/articles/P…
This raises the question: if covid Abs can cross react with Dengue antigens, can the reverse happen? This wld be a huge problem because everyone knows Delhi is endemic to Dengue and half the pop probably has Dengue antibodies which cld falsely react with the covid serology kit.
Turns out this can happen and has been reported! This should be more widely shared since this has huge implications for serosurveillance, and it wld be pretty simple to make sure the Kavach kit doesn't also have this issue.
medrxiv.org/content/10.110…
The same group used computer modelling to further bolster this, while throwing up another probability? Can Dengue antibodies protect us by preventing binding of Sars-cov2 to ACE2 receptor??
doi.org/10.31219/osf.i…
Update: interesting data from Peru might also support this hypothesis. (ie false positive results due to prior exposure to Dengue)
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