5th and 6th Sero Survey of Delhi: Vaccine Activated Antibodies Enhancement

The results of all six serosurveys of Delhi (India) have been analysed. The first serosurvey held in June-July 2020 found seroprevalence in 22.9% population. The second, third, and fourth survey conducted in August, September, and October registered 29.1%, 25.1%, and 25.5% seropositivity, respectively. The seroprevalence was increased to a larger extent of 56.1% in the fifth (January 2021) survey due to the accumulation of antibodies among the residents in three pandemic waves that hit the city in June, September, and November 2020. The last and the fourth bigger wave that hit the city in April 2021 caused almost all (97%) citizens to develop antibodies against the natural COVID-19 infection. The seroprevalence in women was marginally higher (90%) than in men (88%). The seroprevalence was highest (92%) among the individuals above 50 years of age followed by 18-49 years of age (90%) and 82% in below 18 years of age. The residents who were vaccinated with Covishield produced slightly higher antibodies (95%) than Covaxin (93%). In Delhi,one dose or two doses vaccination could increase seroprevalence to 95% that was the maximum which vaccination could generate. The unvaccinated population had seroprevalence of 85%. A maximum enhancement of 13% seroprevalence was recorded upon vaccination with one or two doses.