New Covid Variants: What to Know About BA.2.86 and EG.5

Concern is rising about the Covid-19 variants EG.5 and BA.2.86. In August, EG.5 became the dominant variant in the United States, and the World Health Organization classified it as a “variant of interest,” meaning it has genetic changes that give it an advantage and its prevalence is growing.

BA.2.86 is much less widespread, making up only a tiny fraction of cases, but scientists are alarmed by how many mutations it carries. So how worried should people be about these variants?

EG.5

While severe illness in older adults and people with underlying conditions is always a concern, as is long Covid in anyone who gets infected, experts say EG.5 does not pose a substantial threat — or at least no more of one than any of the other major variants currently circulating.

“It’s a concern that it’s increasing, but it doesn’t look like something that’s vastly different from what’s already been circulating in the U.S. for the past three to four months,” said Andrew Pekosz, a professor of molecular microbiology and immunology at Johns Hopkins University Bloomberg School of Public Health. “So I think that’s what tempers my concern about this variant, at this point in time.”

Even the W.H.O. stated in its announcement that, based on the available evidence, “the public health risk posed by EG.5 is evaluated as low at the global level.”

The variant was identified in China in February 2023 and was first detected in the United States in April. It is a descendant of the Omicron variant XBB.1.9.2 and has one notable mutation that helps it to evade antibodies developed by the immune system in response to earlier variants and vaccines. That advantage may be why EG.5 has become the dominant strain worldwide, and it could be one reason Covid cases have been rising again.

That mutation “may mean that more people are susceptible because the virus can escape a little bit more of that immunity,” Dr. Pekosz said.

But EG.5, which has also been called Eris, does not appear to have any new capacities when it comes to its contagiousness, its symptoms or its likelihood of causing severe illness. Diagnostic tests and treatments such as Paxlovid continue to be effective against it, Dr. Pekosz said.

Dr. Eric Topol, executive vice president of Scripps Research in La Jolla, Calif., said he isn’t overly worried about the variant; however, he would feel better if the new vaccine formulation, which is expected to be rolled out in the fall, was already available. The updated booster was developed based on another variant that is genetically similar to EG.5. It is expected to provide better protection against EG.5 than last year’s shot, which targeted the original coronavirus strain and a much earlier Omicron variant that is only distantly related.

“My main concern is for the people at high risk,” Dr. Topol said. “The vaccines that they’ve had are too far removed from where the virus is right now and where it’s going.”

BA.2.86

The other new variant that scientists are watching closely is BA.2.86, nicknamed Pirola. Descended from a different Omicron variant, BA.2.86 has been definitively tied to 29 cases of Covid across four continents, but experts suspect it is more widespread.

Scientists are particularly concerned about this variant because of the number of mutations it carries. Many of them are in the spike protein, which is what the virus uses to infect human cells and what our immune systems use to identify it. According to Jesse Bloom, a professor at the Fred Hutchinson Cancer Center who specializes in virus evolution, the mutations in BA.2.86 represent “an evolutionary jump similar in size” to the changes in the first Omicron variant compared to the original coronavirus strain.

Data recently released on X (formerly Twitter) by scientists in China showed that BA.2.86 is so different from previous versions of the virus that it easily escapes antibodies produced in response to earlier infections — even more than EG.5 does. The data (which have not yet been published or peer-reviewed) suggest that the updated vaccine will be less effective against it, too.

Before you despair, the research also indicates that BA.2.86 may be less infectious than other variants, though studies conducted in cells in a lab don’t always correspond to how a virus behaves in the real world.

“One possible scenario is BA.2.86 is less transmissible than current variants, and so never spreads widely,” Dr. Bloom wrote in an email to The New York Times. “However, there is also a chance that the variant will spread widely — and we will just have to wait for more data to know.”