The global surge in the omicron (B.1.1.529) variant has resulted in many individuals with hybrid immunity, that is, immunity developed through a combination of SARS-CoV-2 infection and vaccination. Restricting the spread of SARS-CoV-2 infection and preventing severe COVID-19 remains a global priority.
This systematic review and meta-regression aimed to study the magnitude and duration of the protective effectiveness of previous SARS-CoV-2 infection and hybrid immunity against infection and severe disease caused by the omicron variant.
The study findings indicate both previous infection alone and previous infection combined with previous vaccination (i.e., hybrid immunity) conferred rapidly waning protection against SARS-CoV-2 infection with the omicron variant. Nonetheless, it provided high and sustained protection against hospital admission or severe disease due to the omicron variant. Previous infection was found to provide higher protection against reinfection and more sustained protection against hospital admission or severe disease than vaccination alone. However, individuals with hybrid immunity had the highest magnitude and durability of protection against all outcomes, emphasizing the importance of providing vaccination to previously infected individuals.
