The Lancet Infectious Diseases –
Since April, 2022, BA.2.12.1, BA.4, and BA.5 subvariants of the omicron (B.1.1.529) SARS-CoV-2 variant of concern have been spreading globally with increased viral fitness and transmissibility. Omicron BA.5 subvariant is currently the predominant COVID-19 threat worldwide. With the emergence of the antigenically distinct variants of concern, either natural immunity or first-generation vaccine-induced immunity has failed to prevent transmission effectively. Booster (third or fourth) doses of vaccine play an important role in preventing symptomatic infection, although the boosting effect only lasts for several months. Hybrid immunity refers to the immune protection in individuals who have had one or more doses of a COVID-19 vaccine and at least one SARS-CoV-2 infection before or after the first vaccination.