[Editorial Analysis] Banking on serology: On seroprevalence studies

Mains Paper 2: Health
Prelims level: Serology survey
Mains level: Key findings from the Serological survey

Context:

• A recent serology survey that scientists used to estimate the spread of COVID-19 in Mumbai has found that nearly three in five, or 57% of those tested in slums had been exposed to the virus and had developed antibodies against it as compared to only 16% of those tested in residential societies.

Key findings:

• Results from Delhi’s seroprevalence study, earlier this month, found that nearly a quarter of the 21,000-odd samples tested had been exposed to the virus and some of the densest districts had over 20% prevalence.

• Of the nearly 7,000 tested in Mumbai, nearly 61% were slum-dwellers and the higher prevalence of the virus there showed that — as expected — those living in the densest urban agglomerations were most likely to have been infected by it.

• A large proportion of those in whom antibodies were detected — the numbers aren’t known — were asymptomatic and this pointed to the fact that the fatality rate in Mumbai may be “as low as 0.05-0.10 per cent, instead of the existing 5.5 per cent,” as per an estimate accompanying the results of the survey.

Surveys conducted by various states:

• Such serological surveys are increasingly being used by States.

• Ahmedabad’s civic body conducted one to conclude that only 17% of the city had been likely exposed to the virus and Tamil Nadu too is in the midst of conducting such a survey.

• A dominant theme driving State bodies that commission such surveys is to check for levels of ‘herd immunity’, or if 60%-70% of the population have encountered the infection.

• The argument is that this degree of exposure will, akin to a vaccine, also protect the rest of those uninfected.

• But given the absence of knowledge about how long antibodies last and the extent to which they protect from fresh infections, herd immunity isn’t a precise science and not something that ought to be pursued by a state as a matter of policy.

What is a serological survey?

• A serological survey is an antibody test conducted on a sample of the population to assess how many people have been affected. As it is difficult to determine the infection rates of a population based on RT-PCR and Rapid antigen tests, serological surveys are the best bet for the government to ready a response.

What is an ELISA antibody test?

• The ELISA testing kit was developed by National Institute of Virology, Pune along with Zydus Cadila.

• The kit tests for IgG and IgM antibodies in the population. It’s reliability is tested using two indicators: specificity and sensitivity.

• The test, according to literature, has a 97.7% specificity and 92.1% sensitivity.

Crude pointers:

• It is four months since India got its first 100 cases and very early in May, the Indian Council of Medical Research’s survey had shown that the number of those infected by the virus were many multiples of those that were being reflected in official confirmed-case statistics.

• The unrelenting advance of the virus shows that while it is much less of a killer, in aggregate, than expected, it spares few from infection.

• Therefore, in the absence of a reliable vaccine, the vast majority of people everywhere — irrespective of peaks and ebbs in daily caseloads — continue to be vulnerable.

• Serology surveys can at best be crude pointers to chronicle the progress of the pandemic and not a psychological palliative.

Conclusion:

• The virus isn’t as lethal as originally feared, but is more infectious than previously believed

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Prelims Questions:

Q.1) With reference to the serological survey, consider the following statements:

1. A serological survey seeks to assess the prevalence of disease in a population by detecting the presence of specific antibodies against the virus.

2. The test indicates past and active infections.

Which of the statements given above is/are correct?
(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2
Answer: A

Mains Questions:

Q.1) What is a serological survey? What is an ELISA antibody test?

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