South African researchers have found that, compared to Omicron BA.1 and earlier infections, those caused by Omicron BA.4 and BA.5 do not have an increased risk of hospitalisation for severe disease or death.
The study, which appears online in the medRxiv server, aimed to compare clinical severity of Omicron BA.4/BA.5 infection with BA.1 and earlier variant infections among laboratory-confirmed SARS-CoV-2 cases in the Western Cape, South Africa, using timing of infection to infer the lineage/variant causing infection.
In their study, the researchers included public sector patients aged 20 years or older with laboratory-confirmed COVID between 1 and 21 May 2022 (for the BA.4/BA.5 wave) and equivalent prior wave periods. They compared the risk for death and severe hospitalisation/death (all within 21 days of diagnosis), adjusting for for demographics, comorbidities, admission pressure, vaccination and prior infection.
Comparing 3793 patients from the BA.4/BA.5 wave and 190 836 patients from previous waves the risk of severe hospitalisation or death was similar in the BA.4/BA.5 and BA.1 waves (adjusted hazard ratio [aHR] 1.12). Both Omicron waves had a lower risk of severe outcomes than previous waves. They also found that both prior infection (aHR 0.29) and vaccination (aHR 0.17; 0.40 for boosted vs no vaccine) were protective.
Overall, the researchers found that COVID disease severity was similar for the BA.4/BA.5 and BA.1 periods in the context of growing immunity against SARS-CoV-2 due to prior infection and vaccination, which were both strongly protective.
