Repeated vaccination of inactivated SARS-CoV-2 vaccine dampens neutralizing antibodies against Omicron variants in breakthrough infection | Cell Research (nature.com)

A recent study by Chinese researchers compared neutralizing antibody levels in people who experienced breakthrough infection after receiving either two or three doses of inactivated SARS-CoV-2 vaccine during the Omicron BA.2 wave in Shanghai. The study cohort consisted of 135 individuals in Shanghai who were infected with the Omicron BA.2 variant between March and June 2022. Of these individuals, 24 had never received a SARS-CoV-2 vaccine, 56 had received two doses, and 55 had received three doses prior to infection. 

The authors found that NAb titers against the Omicron BA.2, BA.4, and BA.5 variants were significantly lower in the 3-dose group compared to the 2-dose group, despite comparable NAb titers against the original SARS-CoV-2 strain. The authors suggested that repeated vaccination with inactivated virus vaccine may dampen the immune response to a new antigenically related but distinct viral strain, reflecting the “original antigenic sin” phenomenon described in the influenza field. The authors noted that careful consideration should be taken when designing future vaccination and booster strategies. The authors also reported that the unvaccinated group experienced more severe clinical symptoms compared to the vaccinated groups, which mostly presented mild symptoms.

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