Compared with the earlier Omicron BA.2 subvariant, currently dominant Omicron BA.5 is linked with higher odds of causing a second SARS-COV-2 infection regardless of vaccination status, a study from Portugal suggests.
From late April through early June, researchers there studied 15,396 adults infected with the BA.2 variant and 12,306 infected with BA.5. Vaccines and boosters were equally effective against both sublineages, according to a report posted on this week on medRxiv ahead of peer review.
However, 10% of BA.5 cases were reinfections, compared to 5.6% of BA.2 cases, which suggests a reduction in protection conferred by previous infection against BA.5 compared to BA.2, the researchers said. Moreover, the vaccines appeared to be less effective in reducing the risk of severe outcomes for BA.5 compared with BA.2.
“Among those infected with BA.5, booster vaccination was associated with 77% and 88% reduction in risk of COVID-19 hospitalization and death, respectively, while higher risk reduction was found for BA.2 cases, with 93% and 94%, respectively,” the researchers wrote. While “COVID-19 booster vaccination still offers substantial protection against severe outcomes following BA.5 infection,” they said, their findings provide “evidence to adjust public health measures during the BA.5 surge.”