Young and middle-aged adults who were infected with earlier versions of the Omicron variant of the coronavirus are likely to have “strong” protection against reinfection with the currently dominant Omicron BA.4 and BA.5 subvariants, researchers say.

That will not be the case if they were infected with a variant that circulated before Omicron, however, according to a study from Qatar. Researchers there found that after taking vaccination status into account, infection with a pre-Omicron version of SARS-CoV-2 appeared to be only 15.1 per cent effective at preventing a symptomatic BA.4/BA.5 reinfection and 28.3 per cent effective at preventing any BA.4/BA.5 reinfection.

STUDY DID NOT ASSESS SEVERITY OF REINFECTION

A previous Omicron infection, however, was 76.1 per cent effective against symptomatic BA.4/BA.5 reinfection and 79.7 per cent effective against any BA.4/BA.5 reinfection. The study did not assess the severity of reinfection. In a report posted on medRxiv on Tuesday (July 2) ahead of peer review, the researchers point out that the findings may not be applicable in older people, given that in Qatar only nine per cent of the residents are older than 50.

The study also showed that protection from infections with earlier pre-Omicron variants was weaker against BA.4/BA.5 than it was against BA.1/BA.2, “indicating that these two new variants have greater capacity to escape the immune-system response,” said study leader Laith Jamal Abu Raddad of Weill Cornell Medicine-Qatar.