Effectiveness of the COVID-19 vaccines against severe disease with Omicron sub-lineages BA.4 and BA.5 in England

The Omicron sub-lineages BA.4 and BA.5 were first detected in England in April 2022. A case surge followed despite England having recently experienced waves with BA.1 and BA.2. This study used a whole population test-negative case-control study design to estimate the effectiveness of the vaccines currently in use as part of the UK COVID-19 vaccination programme against hospitalisation following infection with BA.4 and BA.5 as compared to BA.2 during a period of co-circulation. Incremental VE was estimated in those vaccinated with either a third or fourth dose as compared to individuals with waned immunity who had received their second dose at least 25 weeks prior. Vaccination status was included as an independent variable and effectiveness was defined as 1-odds of vaccination in cases/odds of vaccination in controls. During the study period, there were 32,845 eligible tests from hospitalised individuals. Of these, 25,862 were negative (controls), 3,432 were BA.2, 273 were BA.4, 947 were BA.5 and 2,331 were either BA.4 or BA.5 cases. There was no evidence of reduced VE against hospitalisation for BA.4 or BA.5 as compared to BA.2. The incremental VE was 56.8% (95% C.I.; 24.0-75.4%), 59.9% (95% C.I.; 45.6-70.5%) and 52.4% (95% C.I.; 43.2-60.1%) for BA.4, BA.5 and BA.2, respectively, at 2 to 14 weeks after a third or fourth dose. VE against hospitalisation with BA.4/5 or BA.2 was slightly higher for the mRNA-1273 booster than the BNT162b2 booster at all time-points investigated, but confidence intervals overlapped. These data provide reassuring evidence of the protection conferred by the current vaccines against severe disease with BA.4 and BA.5.