Durability for 12 months of antibody response to a booster dose of monovalent BNT162b2 in adults who had initially received 2 doses of inactivated vaccine

This study examined the strength and durability of antibody responses in 277 adults who received a heterologous third dose of the BNT162b2 vaccine, following two doses of an inactivated vaccine. Neutralizing antibody levels against both the ancestral virus and Omicron BA.2 subvariant decreased from one month to 6 months after the third dose, and were then maintained at 12 months. Participants who received both a fourth dose and reported a SARS-CoV-2 infection had the highest antibody titers at 365 days after the third dose. Individuals with chronic medical conditions had lower antibody levels against the Omicron BA.2 subvariant at 12 months after the third dose. The results suggest that the heterologous third dose provides durable neutralizing antibody responses, which may be influenced by subsequent infection or vaccination and pre-existing medical conditions. These findings may help explain the differences in immune protection between vaccination and natural infection.