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LATEST NEWS UPDATES | Serosurveys underestimate building of herd immunity -MS Seshadri & T Jacob John

Serosurveys underestimate building of herd immunity -MS Seshadri & T Jacob John

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published Published on Nov 3, 2020   modified Modified on Nov 3, 2020

-The Hindu

Antibody prevalence data derived from serosurveys must be interpreted with caution and correction factors

The theory behind population-based serological surveys (seroprevalence surveys or serosurveys) to detect the prevalence of antibodies against  COVID-19 is robust. Their purpose is to measure the proportion of a population already infected, as evidenced by antibody positivity. When applied on a national scale, a random sample of the entire population is tested. Then, the data are extrapolated to the whole population.

‘Random’, according to the dictionary, means something without a deliberate order. In biostatistics, it means each individual has an equal probability of getting selected. Statisticians stratify the population and select a random sample from all strata so that the prevalence figure obtained is representative of the whole population. The result of random sample serosurveys can be confidently extrapolated to obtain national-level prevalence of antibodies.

What antibody tests say

Unfortunately there are problems with the antibody tests. Antibodies are the footprints of the host’s response to virus infection. Their presence in the blood-serum confirms past infection. However, test results for antibodies throw up surprises. Antibody prevalence data derived from serosurveys must be interpreted with caution and correction factors.

The virus carries several antigens, both on the surface and internally. The body responds to all of them. Four antigens selected to detect antibodies are spike protein (S1, S2), receptor-binding domain (RBD) and nucleocapsid (N). An antibody against each antigen has its own time of appearance, duration in blood and rate of decay over time. Moreover, detection of antibodies does not correlate well with the protective virus-neutralising function of immunity. Testing for virus-neutralising antibodies is not an option, since handling the virus is risky for lab personnel. It is prohibited in clinical labs and restricted to selected research labs.

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The Hindu, 3 November, 2020, https://www.thehindu.com/opinion/op-ed/serosurveys-underestimate-building-of-herd-immunity/article33005833.ece?homepage=true


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