By Aidin Vaziri

Two new immune-evasive coronavirus variants are now responsible for more than half of the COVID-19 cases in the United States, contributing to a wave of infections just ahead of the holidays.

The predominant omicron subvariant, HV.1, has been steadily circulating since early September. But it is being overshadowed by the rapid growth of the JN.1 variant, recently disaggregated from its parent BA.2.86.

Accounting for 21.4% of new cases last week — almost triple the estimated 8% reported over Thanksgiving — JN.1 exhibits increased immunity evasion compared with earlier SARS-CoV-2 strains, according to a risk assessment from the U.S. Centers for Disease Control and Prevention.

“We continue to see this COVID virus change,” Mandy Cohen, director of the CDC, said at a media briefing this week. “In August of this year, we probably saw one of the larger changes to the COVID virus at that time, and what we’ve seen lately in the last couple of weeks is an offshoot of that August variant.”

JN.1 linked to rising COVID-19 cases nationally

In what has become a predictable pre-winter pattern, COVID-19 cases are climbing around the country. Weekly emergency department visits have increased by more than 57% in the past month, reaching 51,708 for the week ending Dec. 9. Wastewater data from the CDC indicates a high concentration of SARS-CoV-2 virus levels nationwide, approaching figures observed last December.

“The continued growth of JN.1 suggests that it is either more transmissible or better at evading our immune systems,” the CDC said in its assessment.

JN.1 has surpassed the threshold of 50% of cases in some European countries, raising concerns about a potential surge in infections around the new year, similar to the first omicron wave two years ago.

“Given current spread patterns, we expect JN.1 to become the next dominant variant worldwide,” Katelyn Jetelina, a scientific adviser to the CDC, said in her latest “Your Local Epidemiologist” newsletter.

JN.1 designated as a variant of interest

Recently designated a variant of interest by the World Health Organization, JN.1 possesses more than three dozen mutations in its spike protein compared with XBB.1.5, which took off a year ago. That’s a similar level of evolution demonstrated by BA.2.86, which caused considerable concern this summer but ultimately did not pose a significant threat.

“It has a growth advantage, but this is what we expect from variants that are classified as variants of interest,” Maria Van Kerkhove, the WHO’s technical lead for COVID-19, said during a briefing last month. “In terms of severity, we don’t see a change in the disease profile of people infected with BA.2.86 and its sublineages, including JN.1, but it is one, of course, one to watch.”

Although COVID-19 poses less of a threat than during previous pandemic waves, due to immunity afforded by vaccination and previous infection, approximately 1,000 Americans continue to die of the virus weekly, according to CDC data.

“This is kind of one of these things like the last 10 hurricanes that didn’t hit. It’s not like the next one might not be a doozy,” said Dr. Bob Wachter, the chair of the department of medicine at UCSF. “I think the most interesting thing about the past year and a half — after the first two years was just one curveball after another — is that it has been pretty stable and pretty predictable. There were a lot of variants that could have been the big one and none of which were. That may be giving us some sense of false reassurance.”

Uncertainties surround symptoms and risks of JN.1

The CDC says there’s no evidence JN.1 presents an increased risk compared with other circulating variants. But the agency also cautioned that it does not know whether the strain causes different symptoms from previous coronavirus offshoots.

“The types of symptoms, and how severe they are, usually depend more on a person’s immunity and overall health rather than which variant causes the infection,” the CDC said in its assessment.

Despite concerns about JN.1’s transmissibility, some experts express hope the strain may become less virulent over time as part of the virus’ overall evolution. There have been hundreds of mutations to the SARS-CoV-2 virus since it first appeared more than three years ago, and many strains have disappeared.

“This particular strain may be more transmissible than the original strain, but it has been less virulent,” said Dr. Yvonne Maldonado, an infectious disease expert at Stanford. “We don’t know whether that’s just because it’s less virulent or whether it’s less virulent and there is more immunity in the population. I think it’s a combination of those two things.”

Maldonado said she hopes “we are seeing the beginning of it receding into the background like a lot of other nuisance cold viruses. That’s clearly not where we are yet, but we hope the trend is in that direction.”

New COVID shots provide some protection against JN.1

Initial data suggests that new COVID-19 shots targeting XBB variants offer protection against BA.2.86, so experts anticipate similar protection levels against JN.1. However, vaccination rates for the updated shot are low, particularly among vulnerable demographics.

Only 16% of U.S. adults and 7% of children have received the updated vaccine as of last week. Among adults ages 65 and older, only one-third have gotten the new shot, compared with 94.4% who completed the primary series of the original vaccine. Those figures are too low, said CDC director Cohen.

The same prevention measures that worked against previous coronavirus strains continue to apply to newer variants, including JN.1. Public health authorities advise staying up to date with vaccinations, using high-quality masks in crowded indoor environments, refraining from public activities when sick, adhering to regular handwashing practices, and getting tested, especially ahead of social events where more vulnerable people may be present.

“Protection from having COVID before and from being vaccinated has decreased over time. So, you need that new vaccine to sort of boost back up your immune system,” Cohen said. She added, “It’s such an important tool to protect our seniors. They are at the highest risk of something going sideways with these viruses.”