Two closely related variants, EG.5 and HV.1, now comprise roughly half of the Covid-19 cases in the United States.
EG.5 became the dominant variant nationwide in August. At that time, the World Health Organization classified it as a “variant of interest,” meaning it has genetic changes that give it an advantage and its prevalence was growing. Since then, the variant appears to have plateaued, holding steady at about 20 to 25 percent of cases in September and October.
HV.1 emerged in the United States at the end of the summer and has progressively made up a larger proportion of the circulating virus. According to the Centers for Disease Control and Prevention, it overtook EG.5 as the dominant variant last week, and now accounts for one in four Covid cases.
Experts have also been watching two other variants, BA.2.86 and JN.1, that make up only a tiny fraction of cases but scientists say carry an alarming number of mutations.
How worried should people be about these variants?
EG.5 & HV.1
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 and HV.1 do not pose a substantial threat — or at least no more of one than any of the other major variants that have circulated this year.
The EG.5 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 mutation “may mean that more people are susceptible because the virus can escape a little bit more of that immunity,” said Andrew Pekosz, a professor of molecular microbiology and immunology at Johns Hopkins University Bloomberg School of Public Health.
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. Perhaps more important, the new vaccines, which target a related XBB variant, appear to produce a sufficient number of antibodies that work against EG.5.
HV.1 is descended from EG.5 and is highly similar to it. There isn’t data yet on how well the new vaccines perform against HV.1, but Dr. Dan Barouch, the head of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center in Boston, said he doesn’t anticipate it will be substantially different from their efficacy against EG.5.
Given the variants’ similarity, it’s unclear exactly how HV.1 has overtaken EG.5, but one of the few additional mutations in HV.1 has likely given it an edge over its predecessor. “Whenever a new variant dominates, then by definition it has an advantage,” Dr. Barouch said. “And the advantage is either increased transmissibility or increased immune escape.”
BA.2.86 & JN.1
Another variant that scientists were watching closely earlier this fall was BA.2.86, nicknamed Pirola. Experts were initially worried about this variant because of the number of mutations it carries 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.
Adding to the concern, early data indicated that the new vaccines may not be very effective against BA.2.86. However, evidence has since emerged that antibody levels produced in response to BA.2.86 are on par with those developed in response to EG.5, suggesting that the vaccines will be sufficiently protective against it. Another study found that BA.2.86 may not be as transmissible as other forms of the virus.
Consequently, BA.2.86 has not taken hold like scientists worried it might; currently, there are no cases of it reported on the C.D.C. variant tracker. Dr. Bloom said that it is not uncommon for new variants to fizzle out instead of spreading widely.
Just like EG.5 evolved to produce HV.1, JN.1 has recently emerged from BA.2.86. According to data released Oct. 18 on X (formerly Twitter) by scientists in China, JN.1 carries a mutation that gives it extra immune-evading capabilities, but it doesn’t appear to bind to human cells as well. Time will tell if JN.1 gains traction or follows the path of BA.2.86.
More than the risk conferred by any individual variant, it is the rapid rate of virus evolution that is most concerning to Trevor Bedford, a professor in the vaccine and infectious disease division at the Fred Hutchinson Cancer Center. “No single variant has been that impactful,” he said, “but the overall accumulation of these mutations is having significant impact.”
