Kerala has lowest exposure to coronavirus
NEW DELHI: Kerala has had the lowest exposure to Sars-CoV-2, according to true infection estimates based on serological studies, new data by the Union government showed on Wednesday, with only 44% of the population projected to have been infected till early July compared with nearly 67% across the country as a whole.
The results, based on the study of how many people had antibodies in a survey involving nearly 29,000 people, appear to explain Kerala’s current high numbers and suggest the state was able to detect true infections better than any other region. The study was carried out by the Indian Council of Medical Research (ICMR).
The overall sero survey results were released last week by the Centre and suggested two out of every three Indians may have been exposed to the virus. If extrapolated, this would mean roughly 900 million people have been infected by the virus; India’s official Covid-19 count on July 10 (when the survey ended) was 30 million. Including Kerala, the states with the three lowest estimated population exposure were Assam (50%) and Maharashtra (58%). The states with the highest exposure were Madhya Pranot desh (79%), Rajasthan (76.2%) and Bihar (75.9%).
“(The finding) reinforces my point that case numbers mean very little without sero surveys to inform what fraction is being detected,” said Anurag Agarwal, director of the Institute of Genomics and Integrative Biology (IGIB).
He added that this also means the second wave will “run longer for Kerala and Maharashtra because of less steep rise”.
To be sure, the fourth round of the sero study included those who received vaccines. While the data released on Wednesday did give a split between those with natural exposure and those with vaccine-mediated antibodies, the information released last week suggests the latter accounts for a very small proportion: Of the 67.6% who had antibodies overall, 62% were not vaccinated, officials said at the time. According to experts, current infection trends and the new data by the health ministry offer two important insights: Kerala may have the least amount of under-reporting, and it has the most number of vulnerable people at present.
“India was able to detect only 1 in 33 cases as of May 31st as estimated from the 4th ICMR serosurvey — Bihar: 1/134; UP; 1/100; MP: 1/86. Detection was much better in Kerala (1/6) and Maharashtra (1/12). Unfortunately, the fingers keep pointing to MH & KL. For detecting cases better?” Rijo M John, a heath economist, wrote on Twitter.
Having antibodies reduces the chances of infection almost completely, and experts said last week it could explain why cases have been falling, although they urged caution, pointing to the nearly 400 million people who remain vulnerable to the virus.
Kerala’s outbreak followed a similar trajectory as the nationwide second wave. But since mid-June, the test positivity rate levelled out at around the 10-12%. At the same time, this metric fell drastically across the country.
Taken together with the serology estimates of the true spread, this also means the virus spread more gradually within Kerala, helping flatten the curve of infections, while it spread rapidly in other parts of the country.
A second expert said study findings were not surprising: “Kerala implemented good Covid-appropriate behaviour and strict lockdown since the first wave. The cases went down in places such as Bihar, UP, and Delhi not because people started following Covid-appropriate behaviour but because a significant proportion was already exposed to the infection,” said Dr Sanjay Rai, head of the department of community medicine of the All India Institute of Medical Sciences.
In the last two weeks, the number of new cases in the state has risen by 28%, which could partly be due to increased testing – over the same duration, the number of daily tests has gone up by an average of 10%, while the positivity rate has risen by 1.8%. It could also be on account of Covid-inappropriate behaviour, with the state government rashly relaxing restrictions on account of the festival of Bakrid.