JN.1 now accounts for almost half of US Covid cases

As the holidays come to an end and cases of Covid-19 begin to rise, a variant called JN.1 has now become the most common strain of the virus spreading across the United States.

JN.1, which emerged from the BA.2.86 variant and first discovered in the United States in September, was responsible for 44 percent of Covid cases nationwide by mid-December, up from about 7 percent in late November, according to data from the Centers for Disease Control and Prevention.

To some extent, this jump is expected. “It takes some time for variants to take off,” said Dr. William Schaffner, an infectious disease specialist at Vanderbilt University Medical Center. “Then they accelerate, they spread widely, and just as they do, a new variant emerges after a few months.”

JN.1’s momentum this month suggests it may be more transmissible or better at evading our immune system than other variants currently circulating, according to a CDC report published on December 22. The agency said Covid remains “a serious threat to public health,” especially for those who have always been at high risk for serious illness, such as older adults, infants, people with compromised immune systems or chronic medical conditions and those who are pregnant.

As far as experts can tell, JN.1 doesn’t appear to cause serious illness in most other people, although even a mild case can still leave you feeling “pretty miserable for three or four days,” said Dr. Schaffner. The symptoms of a JN.1 infection are similar to those caused by previous Covid variants, including coughing, fever, body aches and fatigue.

To protect yourself from infections and serious illnesses, experts continue to recommend wearing masks, improving indoor ventilation if possible, staying home when sick and getting the latest Covid vaccine.

Preliminary research shows that the updated Covid vaccines released in September produce antibodies effective against JN.1, which is distantly related to the XBB.1.5 variant the vaccines were designed for. People may not build up as many antibodies to JN.1 as they do to XBB.1.5, but the levels should still lower the risk.

“For those recently infected or boosted, cross-protection against JN.1 should be significant, based on our laboratory studies,” said Dr. David Ho, a virologist at Columbia University who led the research on JN.1 and Covid vaccines, which was released as a preprint paper in early December. Rapid tests also remain a valuable tool, and the CDC has said tests already on the market work well at detecting JN.1.

There are signs of a resurgence in Covid cases. There were just under 26,000 hospital admissions due to Covid in the week of December 10, a 10 per cent increase on around 23,000 hospital admissions the week before. But Covid hospitalizations are still much lower than at the peak of the first Omicron wave in January 2022, and so far only about half as high as during the peak of the tripledemic last winter, when Covid-19, flu and RSV cases all increased at the same time.

It’s too early to know whether JN.1 is responsible for the increase in hospitalizations or if cases are increasing, partly due to an increase in travel and large gatherings for Thanksgiving and the winter holidays.

“When people are sitting close together indoors, having parties, traveling and the like, those are the kinds of conditions where all respiratory viruses, including JN.1, have the opportunity to spread,” said Dr. Schaffner. Covid also generally has some seasonality, he added; countries in the Northern Hemisphere tend to see a drop in cases in the fall before infections and hospitalizations increase again in the winter.

JN.1 will most likely remain the dominant version of the coronavirus throughout the spring, Dr. Schaffner. He and other experts noted that while vaccines provide protection against it and other variants, uptake remains low 18 percent of adults who received the last shots. Experts say everyone should consider getting vaccinated, especially those who are over 65, have weakened immune systems, have health conditions that put them at higher risk for serious illness or are traveling to visit loved ones who may be vulnerable .

“Give yourself a New Year’s gift by getting this vaccine if you haven’t already,” said Dr. Schaffner.