Immune responses against different variants of SARS-CoV-2 including Omicron following 6 months of administration of heterologous prime-boost COVID-19 vaccine

Comparative analysis at one- and six-months post-vaccination showed modest reduction in S1-RBD IgG antibody and NAb titers against B.1, Alpha, Beta and Delta variants in heterologous and homologous vaccine recipients groups. However, significant reduction in NAb titers against Omicron in vaccinees’ sera post-six months underlines need for cautious prospective follow-up.