Protection against Reinfection with the Omicron BA.2.75 Subvariant

This correspondence analyzes the real-world effectiveness of prior SARS-CoV-2 infections in preventing reinfection with the Omicron BA.2.75 subvariant, using national health data from Qatar. A test-negative, case-control design reveals substantially reduced protection from pre-Omicron infections (6.0%), moderate protection from prior BA.1 or BA.2 infection (49.9%), and stronger protection from BA.4 or BA.5 infection (80.6%). Sequential infections, pre-Omicron followed by BA.4/BA.5, conferred the highest protection (91.6%). Protection was greater among vaccinated individuals and those with more recent infections. The findings underscore rapid immune evasion by emerging subvariants and suggest hybrid immunity (vaccination plus Omicron infection) provides superior defense. Authors urge consideration of immune imprinting and timing when evaluating reinfection risk and vaccine strategies.

This correspondence analyzes the real-world effectiveness of prior SARS-CoV-2 infections in preventing reinfection with the Omicron BA.2.75 subvariant, using national health data from Qatar. A test-negative, case-control design reveals substantially reduced protection from pre-Omicron infections (6.0%), moderate protection from prior BA.1 or BA.2 infection (49.9%), and stronger protection from BA.4 or BA.5 infection (80.6%). Sequential infections, pre-Omicron followed by BA.4/BA.5, conferred the highest protection (91.6%). Protection was greater among vaccinated individuals and those with more recent infections. The findings underscore rapid immune evasion by emerging subvariants and suggest hybrid immunity (vaccination plus Omicron infection) provides superior defense. Authors urge consideration of immune imprinting and timing when evaluating reinfection risk and vaccine strategies.