Reinfections With Omicron Sublineages Are Rare, Danish Study Finds

By Reuters Staff

February 23, 2022

COPENHAGEN (Reuters) - Getting infected twice with two different Omicron coronavirus sublineages is possible, but rarely happens, a Danish study suggests.

In Denmark, a more infectious sublineage of the Omicron coronavirus variant known as BA.2 has quickly dethroned the "original" BA.1 version, which is the most common worldwide, but it has remained unclear whether infection with one version of Omicron protects against the other.

A new study, led by researchers at Denmark's top infectious disease authority, Statens Serum Institut (SSI), shows that people infected with BA.1 can get infected with BA.2 shortly afterwards, but that it may be an uncommon occurrence.

"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 more than 40 mutations. While BA.2 accounts for more than 88% of cases in Denmark and 100% of new cases in South Africa, cases have also started to increase around the world.

The reinfections mostly affected young, unvaccinated individuals and only caused mild disease, none of which led to hospitalisations or deaths, the researchers added.

The study, posted on medRxiv ahead of peer review, 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.

In that period more than 1.8 million infections were registered in Denmark.

From a smaller subset of 187 reinfection cases with adequate genomic sequencing information for both infections, the study found 47 instances of BA.2 reinfections shortly after a BA.1 infection. The researchers also detected lower viral titers at the second infection, suggesting some immunity was developed from the first infections.

SOURCE: medRxiv, online February 22, 2022.