New COVID Variant Spreading In US, Experts Explain Risks (Or Lack Thereof)

The new BA.2.86 variant, unofficially known as Pirola is taking hold in the United States.

Between Oct. 28 to Nov. 25, its prevalence increased from 1 to around 9 percent in the United States, according to the U.S. Centers for Disease Control and Prevention (CDC).

The World Health Organization designated Pirola as a variant of interest on Nov. 21, yet it also found the public health risk posed by BA.2.86 to be “low at the global level (pdf).”

Other variants derived from BA.2 include XBB.1.5 which became the dominant strain in early 2023.

The current dominant variant is H.V.1, and it is derived from the variant EG.5, unofficially known as Eris, a previously dominant variant in the United States.

“At this time, BA.2.86 does not appear to be driving increases in infections or hospitalizations in the United States,” the CDC wrote.

Research outside of the United States similarly suggests that Pirola should not be more severe than current variants.

Researcher Yunlong Cao, who holds a doctorate in physical biochemistry from Harvard found that Pirola “exhibits lower cell infectivity” compared to XBB.1.5 and Eris.

A preprint study from Japan found that while Pirola may be more transmissible than Eris a previous dominant variant, it is less likely to cause disease.

Compared to Eris, Pirola has a significantly lower growth efficiency, meaning that it is less capable of replicating itself in the host, the authors wrote.

The substantial number of mutations initially raised concerns among virologists, who feared this variant might partially evade earlier immunity from previous exposure, whether from natural infection or prior vaccination.

However, evidence is still lacking to predict if there will be more immune evasions as well as the severity of future Pirola cases.

Mr. Cao’s own research in mice who have been vaccinated or infected with XBB vaccines showed that the antibodies generated “cannot well recognize and neutralize BA.2.86,” he wrote in a thread posted on the social media platform, X.

However, Pirola had a low cell infectivity, which can affect the variant’s transmission, he added.

In discussion of Mr. Cao’s findings, Mr. Hanage agreed that immune evasion is not a definite indication of more severe infection and transmission.

“Any hopeful virus has to have some immune evasion, because almost everyone has immunity,” he wrote.

The most recent research on Pirola’s immune evasion abilities comes from a series of reports conducted by researchers at Columbia University.

The first study, published in Nature, tested Pirola, XBB1.5, and Eris spike proteins against antibodies produced from a breakthrough XBB infection.

These antibodies conferred robust neutralizing activity against Pirola. The authors also noted that Pirola’s ability to evade immunity was no better than that of XBB1.5 and EG.5.

The same group of researchers then tested antibodies produced from the new XBB1.5 COVID vaccine against several variants, including XBB1.5, Eris, and JN.1, a derivative of Pirola. The findings were published in a preprint.

Eris is currently the most dominant globally and HV.1 succeeded Eris as the dominating variant in the U.S. on Oct. 28.

Like Pirola, the WHO has classified HV.1 as a variant with low public health risk. The variant accounted for about 31.5 percent of all cases in the United States as of Nov. 25.