The rising graph of herd immunity against COVID
INDIA’S latest nationwide sero survey report, which was released last week, has revealed that around 21 per cent of Indians aged above 18 years have been exposed to the coronavirus. This is the third sero survey conducted by the Indian Council of Medical Research (ICMR) since May last year and was conducted on 28,589 people between January 17, 2020 and January 8, 2021 for prevalence of antibodies. The survey also revealed that there was seroprevalence of over 25 per cent among healthcare workers. A serological test is conducted to detect whether a person has antibodies to Sars-Cov-2, an indicator of a past infection. The first test held in May-June last year had revealed that prevalence of antibodies among Indians was a mere 0.73 per cent. The seroprevalence jumped to nearly 7 per cent during the second survey carried out in August and September. The third survey has revealed a jump of over 14 per cent of seroprevalence in three months. This also shows that a huge Indian population is still vulnerable to the virus.
The latest sero survey has found prevalence of antibodies among children aged between 10 and 17 to be 25.3 per cent. The presence of antibodies in people living in rural India was the least at 19.1 per cent. The prevalence among urban slum dwellers was as high as 31.7 per cent, while in non-urban slums it was 26.2 per cent. The study also found that 23.4 per cent of people above the age of 60 had antibodies. More women had antibodies compared to men. While the prevalence rate was 22.7 per cent among women, it was 20.3 per cent among men. The experts have been using the most sensitive test to conduct the survey. With just over a fifth of Indian population having been found to have prevalence of antibodies, there is merit in the warning that India cannot afford to lower the guard against the virus. The threat from the virus was still there and it was necessary that all precautionary measures were adopted to keep the virus at bay.
As a large proportion of the population was still vulnerable to the infection, the need is for continued adherence to the COVID code that makes it compulsory to wear masks, sanitise hands regularly and maintain social distancing. A report published in the Lancet Global Health has said that transmission of the infection was expected to continue in most Indian states till the herd immunity threshold was achieved. The herd immunity can be achieved either by natural infection or vaccination. While this threshold of herd immunity is unknown as of now, most estimates place it above 50 per cent. Indians have done well in fighting the coronavirus and keeping it at bay so far. The longest-ever lockdown ordered by the government helped in keeping the numbers of those affected by the virus under control, though it had a decelerative effect on the economy. With new variants, some of them deadlier than the earlier ones, being found and transmitted from one country to another, Indians need to ensure that all COVID-19 precautions are followed so as to prevent contracting the virus and ensuring it
does not spread.
The sero survey numbers are encouraging. There is a possibility of more Indians having developed antibodies among those who might not have been surveyed. As the number of persons testing positive has been dropping in the past three months, there is a possibility of India having managed to contain the spread of the virus that caused the latest pandemic. With just 1.08 crore total cases, India had less than one per cent of its population affected by the virus. Studies have found that most people afflicted by COVID-19 were asymptomatic. Some others developed symptoms but they preferred to stay away from seeking medical help as they did not want to be
quarantined and recovered, which may have added to the number of those having built antibodies. With the vaccination drive going on, immunity development is expected to be faster. However, as a large population is still at the risk of contracting the virus, appropriate preventive behaviour is absolutely necessary to firmly subdue it.