India corona virus numbers explained: How to read the serological survey results from Mumbai and Delhi

Context:

• Results of two different serological surveys, one in Delhi and the other in Mumbai, were announced.

Finding of the Survey:

• Presence of novel Corona virus-specific antibodies in slightly less than 25 per cent of those tested.
• The serological survey in Delhi tested 21,387 people, and found that 22.86 per cent of these had developed antibodies against Covid19.

Serological tests:

• Look for disease-specific antibodies in an individual.
• Since it is not possible to do a diagnostic test on everyone, the real number of people infected by the disease is not known.
• Every infected person, whether symptomatic or otherwise, develops antibodies against the disease.
• These antibodies remain within the person for a prolonged period, possibly for a few months.
• Detection of these antibodies means the person has been infected with the disease at some stage.

Importance of Serological tests:

• Make informed decisions about the interventions to be used in order to contain the disease.
• Gives them a better understanding of how dangerous the virus is.

Challenge:

• How well can these numbers be extrapolated to the entire populations depend on how representative the survey sample was.
• How uniformly is the disease spread in the population.

Reference: https://indianexpress.com/article/explained/coronavirus-numbers-tracker-serological-survey-delhi-mumbai-6518055/