More women were found to have developed antibodies against COVID-19 compared to men in the fifth and the largest serological survey done by the Delhi government, said Health Minister Satyendar Jain on Tuesday.
Many experts and the Minister said the city is getting closer to attaining herd immunity, but people should still take vaccines as it will provide a better immune response against the virus and also continue to take all precautions.
About 56.13% of over 28,000 people, whose blood samples were collected, have developed antibodies against COVID-19, the results show. This means that 56.13% of the people surveyed had caught the infection at some point and have recovered from it, Mr. Jain said.
When a larger part of the population develops antibodies and becomes immune to the virus, the chain of transmission is broken which reduces the spread of the disease which is called herd immunity. So, a higher value of sero prevalence is favourable.
“About 60-70% seroprevalence is needed to attain herd immunity. But new strains can create a problem. So, 56% sero prevalence is a good sign, but we cannot say that Delhi has attained herd immunity,” said Dr. Arun Gupta, president of the Delhi Medical Council.
But another expert said there is uncertainty on the percentage of the population who should have antibodies to attain herd immunity.
“Earlier we thought that 60-70% sero prevalence was needed to attain it. In the Manaus province in Brazil, there is a sero prevalence of 76%, as per a study. But the pandemic is still raging there, and cases and deaths are high,” said Dr.K. Srinath Reddy, epidemiologist and president of the Public Health Foundation of India (PHFI), Delhi.
“So, considering the Brazil example, we actually don’t know what is the sero prevalence needed to attain herd immunity for this virus. There is a fair amount of uncertainty. We need to maintain our vigilance and not relax,” he said.
“We shouldn’t think that we have reached herd immunity. Let’s wait and see. It’s a new disease. We don’t want to give any wrong idea,” Director General of Health Services of Delhi, Nutan Mundeja, said while releasing the results of the survey.
The Minister also urged people to continue taking precautions and wear masks.
Both Dr. Gupta and Dr. Reddy said people who have developed antibodies can still transmit the virus, and everyone should be careful.
“If you have immunity from antibodies developed naturally or from the vaccine, it protects you from developing severe disease. But the COVID-19 virus can still invade your body and settle in your nose and throat without causing a disease and it can get transmitted to others during this period,” Dr. Reddy said.
Dr. Gupta said even people who have antibodies should take the vaccine. “This survey is quantitative and just shows that 56.13% of people have antibodies, but not the level of antibodies in them. Vaccines create a measured and better level of antibodies in people,” he said.
Of the 11 districts in the city, the south east district was found to have the highest sero prevalence with 62.18% and north district with 49.09% the lowest.
The sensitivity of test used for the survey was more than previous sero surveys and more women were found to have antibodies compared to men.
Blood samples of random people of various age groups from across the city were collected for the survey.