Delhi’s troubling ‘quarter-percent’ result

The TLDR: A massive serological survey of Delhi shows that almost one in four people in the city were infected with the coronavirus at some point. The government thinks this is a good result. Critics beg to disagree. 

First tell me about this survey

The result: The government collected 21,387 samples across 11 districts between June 27 and July 10. It found 23.48% of those tested have antibodies. This means their bodies were exposed to the virus, triggering an immune response. 

The methodology: Delhi residents were administered the IgG Enzyme Linked Immunosorbent Assay (ELISA) test. This is a highly sensitive test that only detects the presence of antibodies. It is not used to check if someone has Covid. And the level of antibodies it measures are typically produced two weeks after infection. What this means: that 23.48% likely reflects the number of infections in early June.

The value: The problem with this coronavirus is that many cases are asymptomatic or only display mild symptoms—and therefore go undetected. Serological surveys help fill in this gaping holes in our data:

“From a public health standpoint, knowing how many and who have already been exposed to SARS-CoV-2 gives a clearer picture of how widespread the virus is in local populations. This is extremely useful because public health measures depend on how far coronavirus has already penetrated into the general population.”

Ok, so what does this survey tell us?

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