"We provide evidence that Omicron BA.2 reinfections are rare but can occur relatively shortly after a BA.1 infection," the study authors said.
BA.1 and BA.2 differ by up to 40 mutations. While BA.2 accounts for more than 88 per cent of cases in Denmark, cases have started to increase in the United Kingdom, South Africa and Norway. The reinfections mostly affected young, unvaccinated individuals and only caused mild disease, none of which led to hospitalizations or deaths, the researchers added.
The study, which is not yet peer-reviewed, found 1,739 cases registered between Nov 21, 2021, and Feb 11 this year, where people had tested positive twice between 20 and 60 days apart.From a smaller sample group, the study found 47 instances of BA.2 reinfections shortly after a BA.1 infection. The researchers also detected less virus material at the second infection, suggesting some immunity was developed from the first infections.