Case-controlled study to compare the neutralizing antibody amongst fully vaccinated breakthrough infections in third wave of COVID-19 and asymptomatic healthcare workers

Abstract

BackgroundThe SARS-CoV-2 (COVID-19) pandemic declared in March 2020 continues to impact millions globally. India initiated a large-scale COVID-19 vaccination campaign in January 2021 using the CovishieldTM vaccine. Monitoring neutralizing antibody (NAb) levels is essential for assessing vaccine effectiveness, but data on NAb levels after completing two doses of CovishieldTM are limited. This study aimed to investigate the NAb profile among fully vaccinated individuals. MethodsConducted during the third wave of the pandemic starting in January 2022, this study included individuals who received the first two doses of CovishieldTM and visited the flu clinic or vaccination center. NAb levels were measured using an approved kit and "Blocking ELISA" method. Symptomatic individuals underwent COVID-19 real-time polymerase chain reaction (RT-PCR) testing. ResultsThe study included 299 individuals with a median age of 26 years (IQR-11 years; male preponderance: 81.9%). NAb was detected in 91.5% (n=274) of the participants. The mean neutralizing percentage inhibition was 77.26%±26.26%. Significant relationships were found between neutralizing percentage inhibition and past COVID-19 infection (p=0.0005), blood groups (B+ve had the highest Ab inhibition, p=0.0003), and age (p=0.01). No significant correlation was observed with gender (p=0.11), time since the second vaccine dose (p=0.32), and time from the last COVID19 infection (p=0.48). ConclusionDuring the early stages of the third wave of COVID-19 in India (January 2022), a high seroprevalence of NAb was observed among fully vaccinated individuals. Breakthrough infections occurred but with reduced severity. Breakthrough cases had higher percentage inhibition, high NAb positivity, longer time since the last COVID-19 infection, and older age.