What to Know About the New Covid Variants

HV.1 has overtaken EG.5 as the leading variant in the U.S. Scientists are also watching two other variants, BA.2.86 and JN.1.

Two closely related variants, EG.5 and HV.1, currently comprise nearly 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. The variant peaked in September at about 25 percent of cases and has since slowly started to decline, down to 13 percent in December.

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 in late October, and now accounts for just over 30 percent of Covid cases.

Scientists have also been watching two other variants, BA.2.86 and JN.1, that they say carry an alarming number of mutations. The two variants, which the C.D.C. reports together, make up about 9 percent of cases in the United States and appear to be on the rise.

Here’s what to know 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. New data, published as a preprint paper in December, show that similarity extends to how well the updated vaccines perform against HV.1, suggesting the latest booster also offers some protection against it.

Given the variants likeness, 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,” said Dr. Dan Barouch, the head of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center in Boston. “And the advantage is either increased transmissibility or increased immune escape.”

BA.2.86 & JN.1

Another variant that scientists started watching closely this fall is BA.2.86, nicknamed Pirola. This variant worried experts 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.

BA.2.86 did not take off like scientists initially feared, but just like EG.5 evolved to produce HV.1, JN.1 has recently emerged from BA.2.86 and is spreading quickly. According to preliminary research released in November, JN.1 carries a mutation that gives it extra immune-evading capabilities.

The preprint paper testing how the new vaccines performed against HV.1 also showed that they produced antibodies effective against JN.1, but not as many. “Vaccinations or recent infections decrease but do not fully eliminate the risk” from JN.1, Dr. Bloom said in an email. “It seems quite possible (although not certain) that JN.1 or a closely related virus will become globally dominant over the next few months.”

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.”

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