1 in 4 people in Delhi may have been exposed to COVID-19: Can we achieve herd immunity soon?

With 1,14,000 cases, Delhi is one of the worst affected cities by the COVID-19 in India. However, after a period of a rampant rise in the number of infections which pushed the healthcare system to the verge of collapse, Delhi might be on its road to recovery, with a slowdown in infection rates and a recovery rate which is over 80%. A lot of measures have been introduced by officials to curb the spread, including starting serosurveillance tests, which are to happen monthly going forward. A recent such survey found out it might be possible that a whopping 23.8%, roughly a quarter of Delhi's population may have been already exposed to the deadly SARS-COV2 virus.

A study was done by India’s National Centre for Disease Control (NCDC) to test the level of antibodies in a sample population across the city where it was observed that 23.4% of those surveyed were detected with a high level of infection-fighting antibodies.

For the same, blood samples of 21,387 people were taken randomly and were tested for antibodies in the last week of June.

The test, seroprevalence test is a non-diagnostic tool which is used to check for any trace or past exposure to infection.

It was also observed that a large percentage among those tested were found to be asymptomatic.

If the findings are indeed true, it might show that the rate of infection is far higher than what official figures suggest. An asymptomatic rise in cases may also suggest that a large section of the population may have general immunity against the virus.

Another study done by a private diagnostic laboratory chain, Thyrocare, recently found out that 15% of India's population may have developed antibodies pertaining to COVID-19. India is currently the third-worst affected nation by the pandemic.

While the data reveals that the official figures may not be entirely correct, some experts believe that a high exposure rate, such as this, maybe evidence that the city can reach the stage of herd immunity soon.

A community is said to reach herd immunity when a large percentage of its population gains natural immunity to a said infection (either by getting infected and recovering, with a vaccine or avoiding it altogether), thereby, preventing the spread of the disease. While some peg herd immunity rate at 60%, some studies claimed that herd immunity could be achieved at as low as 43%.

Speaking to a media outlet, leading Indian epidemiologist, J P Muliyil, chairman of the Scientific Advisory Committee of the National Institute of Epidemiology also concurred the same, saying that we might be fast approaching herd immunity.

"The result is pretty encouraging. This is herd immunity. A vaccine is supposed to do this. It is a big number. It can be interpreted as a large number of the population having already been infected. You have to remember that we were expecting that once we reach the herd immunity level, which is close to 50 -60 per cent, the whole thing will settle down. If some old containment areas in Delhi are getting quiet and are not reporting any more cases, we can say that they are getting into the herd level of immunity."

He also asserted saying that a downward spiral in the number of cases being reported in cities like Mumbai and Delhi show positive signs of the virus slowing down:

"I think so (herd immunity can be achieved) faster than we all thought. In a few weeks, we will hopefully find cases dwindling everywhere, at least in Delhi. Even in Mumbai, cases are coming down in most of the containment areas. It means that we are fast approaching herd immunity."

However, testing figures do not mean all possible good news. Dr VK Paul, a member of NITI Aayog said that the statistics point out to a section of the population which is still vulnerable:

"77 per cent people in Delhi is still vulnerable to COVID-19,"

Till then, continuing to practice social distancing and maintaining good hygiene protocols may be our best bet to keep the infection at bay.