“It’s highly unlikely that we will have another major outbreak in Delhi,” Dr Sajnay Rai, professor of community medicine, All India Institute of Medical Sciences, told TOI, pointing out that the survey suggests over half of the capital’s population has been exposed to the virus. “People have developed antibodies through natural infection and it is likely to protect them from infection or severe symptoms for some time,” Rai said, adding, however, that mass immunisation was still a necessity.
A recent sero-survey in parts of Brazil and the United Kingdom also showed a high prevalence of antibodies against the Covid coronavirus. India currently has approved Covishield and Covaxin for emergency use against Covid. Rai headed the clinical trials conducted at AIIMS to test the safety and efficacy of Covaxin. “The vaccines are safe,” he said. “People shouldn’t get complacent. They must get the jab when their time comes for additional protection.”
Dr Suneela Garg, member of the Lancet commission for Covid-19 India vaccination task force, said, “We cannot hope for herd immunity through exposure to the disease. It will come only through mass vaccination,” said Garg, who is a member of India’s Covid vaccination task force.
Herd immunity occurs when a large section of the populace has been affected by a virus and has subsequently become immune through the development of antibodies. They form a layer between the infected and those who aren’t and cause a disruption in the infection chain.
Dr Arun Gupta, president, Delhi Medical Council, cautioned that all care must still have to be taken to wear masks and maintain social distancing because a large number of Delhiites remained susceptible to infection.
The survey to detect antibodies in the 28,000 samples collected from across Delhi’s 11 districts in the fifth sero-prevalence study was conducted at the Institute of Liver and Biliary Sciences. Its director, Dr S K Sarin, told TOI that nearly 25% of the respondents had high levels of antibodies or neutralising antibodies. “The rest had moderate to low levels of antibodies against Covid,” he said, adding that the presence of antibodies in over 50% of the city’s population was a good sign, but in itself did not rule out the need for mass immunisation.