75% exposed to Covid-19 in Bengaluru: Serosurvey

Preliminary results of the serosurvey, which was launched by municipal authorities in early August has shown that over 75% of the sample population in Bengaluru have antibodies for Covid-19.

The sample size included 1,000 people who were vaccinated and another 1,000 who were not. About 30% were under 18 years of age, 50% were aged 18 to 44 and 20% were above the age of 45. The sample group included residents from across the city belonging to various socio-economic groups.

CORONAVIRUS SPECIAL COVERAGE ONLY ON DH

According to sources, over 1,400 people out of the 1,800 members of the sample group registered antibodies for the novel coronavirus. The samples of the remaining 200 are still being tabulated.

“Between 75% and over 80% of the sample population of both vaccinated and unvaccinated groups have registered antibodies to Covid-19,” sources said, specifying that these numbers are from the preliminary report.

According to D Randeep, Special Commissioner (Health), Bruhat Bengaluru Mahanagara Palike (BBMP), the objective of the serosurvey was to determine the effectiveness of vaccinations in generating antibodies and to gauge how many unvaccinated people had been exposed to the novel coronavirus.

The preliminary findings appear to show that vaccinations are inducing an appropriate antibody response in people. At the same time, despite the small sample size, the high seroprevalence score also suggests that a sizable percentage of the city’s population had been infected during the second wave.

The BBMP believes that one causative effect of this seroprevalence score is that it explains the city’s dramatic decline in serious hospitalisation cases.

According to official data, while the number of new Covid-19 cases in the city has fallen by 19% over the last 50 days, the rate of total new hospitalisations has dropped by 36%. BBMP chief commissioner Gaurav Gupta told DH that the final report will be made public in a few days.

Also read: Many passengers from Kerala let into Karnataka without quarantine

Eminent virologist Dr T Jacob John pointed out that True Population Immunity (otherwise known as herd immunity), will be notably higher than values returned by serosurveys.

“Lab assays are effective only up to a certain point when it comes to detecting antibodies from samples. Data suggests that antibodies are detected in only between 65 and 80% of positive cases. Therefore, if Bengaluru’s seroprevalence is over 75%, the true population immunity is likely closer to 85%,” Dr John said.

These immunity levels suggest, statistically, that the probability of a third wave is slim, he added.

However, he stipulated that a third wave is still possible if “a new variant emerges which has an order of magnitude of infectivity greater than the Delta variant.”