NEW DELHI: A first scientific analysis has presented the first signs of community-level protection against Covid-19 emerging in India. The scientists attached with various government institutions tracked new cases in Pune from areas with different — high and low — seroprevalence after 45 days of the serosurvey and found significantly fewer cases emerging in areas with high seroprevalence and more cases from areas with low seroprevalence.
Significantly, they also found 85 per cent of the seropositive people have neutralising or protective antibodies — another measurement done for the first time in India. Pune, with over 3.4 lakh confirmed Covid-19 cases, has been one of the country’s worst hit cities.
The first part of the analysis, made public in August, had said areas reporting high Covid-19 cases in the city had shown nearly 51.5% of the samples tested had antibodies against the virus, making it the highest seroprevalence reported from any city in India till then. People who lived in apartments had somewhat lower prevalence (33%) while the prevalence was found to be 45.3% among the people who had access to independent toilets, as against 62.2% among those who shared toilets.
“As next part of the exercise, we analysed whether areas with high seroprevalence were reporting fewer cases and vice-versa and our findings suggest exactly the same,” said Aurnab Ghoshe, one of the principal investigators of the project, who is attached with the Indian Institute of Scientific Education Research, Pune. Also, he said, nearly 85 % of those who were seropositive had varying degrees of neutralising antibodies with varying degrees suggesting that they have protection against future infections, even though scientists are yet to establish how long the immunity will last.
In the paper, the researchers have noted that seropositivity was extensive but varied widely in the five localities tested, ranging from 35•8% to 66•4%. “Seropositivity was higher in crowded living conditions in slums, and was lower in those 65 years or older,” it says. Also, the infection-fatality ratio was estimated at 0.28% and post survey, Covid-19 incidence was lower in areas noted to have higher seroprevalence.
Substantial virus-neutralising activity was observed in seropositive individuals, but with considerable heterogeneity in the immune response and possible age-dependent diversity in the antibody repertoire.
Despite crowded living conditions having facilitated widespread transmission, the variability in seroprevalence in localities that are in geographical proximity indicates a heterogenous spread of infection, the analysis says. Declining infection rates in areas with high seropositivity suggest population-level protection and is supported by substantial neutralising activity in asymptomatically infected in dividuals, said the scientists.