BA.2.86 subvariant potentially better at causing breakthrough infections: CDC

The recently detected BA.2.86 COVID-19 subvariant may be more capable of causing infections in people who previously contracted the virus or have been vaccinated, according to a risk assessment from the Centers for Disease Control and Prevention (CDC), though it remains unclear if this strain causes more severe illness than others.

First detected last month, a handful of infections caused by BA.2.86 have been reported in the U.S., Denmark, South Africa, the U.K. and Israel. The CDC noted that genomic sequencing of COVID-19 has dropped “substantially” when compared to the past few years, so the spread and occurrence of new strains may go undetected for longer.

So far only two cases from BA.2.86 have been confirmed in the U.S. This newer strain is believed to be descended from the BA.2 “stealth” variant that surged globally early last year.

The updated COVID-19 vaccines are targeted towards strains descending from the XBB Omicron subvariant. The CDC said researchers are evaluating the effectiveness of the updated shots, which are anticipated to reduce severe disease and hospitalizations.

Compared to other strains descended from the Omicron subvariant, BA.2.86 has many more mutations, with the CDC comparing the differences between it and its likely ancestor BA.2 as being similar to the difference between the delta and Omicron variants.

“The large number of mutations in this variant raises concerns of greater escape from existing immunity from vaccines and previous infections compared with other recent variants,” the CDC said in its assessment. “For example, one analysis of mutations suggests the difference may be as large as or greater than that between BA.2 and XBB.1.5, which circulated nearly a year apart.”

The agency added, however, that it’s still too soon to know what real-world impact the recently detected strain will have on immunity.

The World Health Organization has designated the BA.2.86 as a “variant under monitoring,” meaning it has “genetic changes” that indicate early signs of an advantage over other circulating strains, but the true impact remains unclear.