“…In general, our observations are in line with previous reports, which state that humoral responses are higher in the second wave. 7 Surprisingly, a 3.4-fold reduction in the GMT ratio of Delta to B.1 with second wave sera was observed compared with the 4.2-fold reduction of the first wave sera of B.1 to Delta, indicating the immune response against Delta variant imparts a 1.2-fold higher cross-neutralization of Delta variant heterologous strains like B.1. Even though the government of Indian initiated a vaccine drive in January 2021, due to vaccine production challenges, it was insufficient to cover the enormous population by the time Delta variant was spread in the country.…”