The initial findings of the fifth round of serological survey conducted in Delhi suggest that over 56 percent of the people have developed antibodies against Covid-19 implying achievement of herd immunity.

Herd Immunity

• Herd immunity is when a large number of people are vaccinated against a disease, lowering the chances of others being infected by it.
• When a sufficient percentage of a population is vaccinated, it slows the spread of disease.
• It is also referred to as community immunity or herd protection.
• The decline of disease incidence is greater than the proportion of individuals immunized because vaccination reduces the spread of an infectious agent by reducing the amount and/or duration of pathogen shedding by vaccines, retarding transmission.
• The approach requires those exposed to the virus to build natural immunity and stop the human-to-human transmission. This will subsequently halt its spread.

Sero-surveys in Delhi

• The results of the latest serosurvey in Delhi have led researchers and experts to surmise that a large section of the city’s population has already developed antibodies against Covid-19.
• The presence of antibodies among a large percentage of the population could be a reason for the decline in the daily number of Covid-19 cases.
• As more people are able to resist infection, it will help to break the chain of transmission of the virus.
• Five serological surveys have been carried out in Delhi so far, including the present one, which was conducted in January.
• The survey conducted by NCDC in July last year suggested the presence of antibodies in 23 percent of those surveyed.
• In August, the survey conducted by the Delhi government showed 29.1 percent had antibodies.

The relevance of such surveys

• Carrying out repeated serological surveillance on the same population gives an idea of how the disease is behaving.
• It is always good to have surveillance regularly to understand the trends.
• Having robust surveillance is always beneficial, it may not be too close, but it may help us in giving an idea, even of the natural history of the disease.

What do the data suggest about herd immunity?

• Many researchers believe that if 60 percent or more of the population has developed antibodies against Covid-19, there is a possibility of acquiring herd immunity.
• In Delhi, it is quite indicative, as the number of cases is also going down. This shows that we are moving closer towards acquiring herd immunity.

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