Covid variant JN.1 now accounts for nearly half of US cases

As the holiday season draws to a close and Covid-19 cases begin to rise, a variant called JN.1 has become the most common strain of the virus spreading in the United States.

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

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

The momentum of JN.1 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 public health threat,” 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 They are pregnant.

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

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

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

“For those who were recently infected or vaccinated, cross-protection against JN.1 should be decent, based on our laboratory studies,” said Dr. David Ho, a virologist at Columbia University who led the investigation on the JN.1 and Covid vaccines, which was published as a pre-print document in early December. Rapid tests also remain a valuable tool and the CDC has said that tests already on the market work well at detecting JN.1.

There are signs that Covid cases are rising once again. There were just under 26,000 hospitalizations due to Covid the week of December 10, a 10 percent increase from the approximately 23,000 hospitalizations the week before. But Covid hospitalizations remain much lower than during the peak of the first Omicron wave in January 2022, and so far only about half of what they were during the peak of the tripledemic last winter, when Covid -19, the flu and RSV. All cases increased at the same time.

It is too early to know if JN.1 is responsible for the increase in hospitalizations or if cases are increasing in part due to increased travel and large gatherings for Thanksgiving and the winter holidays.

“When people gather indoors, close to each other, have parties, travel and things like that, those are the types of circumstances where all respiratory viruses, including JN.1, have opportunities to spread” said Dr. Schaffner. Covid in general also has a certain seasonality, he added; Countries in the northern hemisphere tend to see a lull in cases in the fall before infections and hospitalizations rise again in the winter.

JN.1 will most likely remain the dominant version of the coronavirus until spring, Dr. Schaffner said. He and other experts noted that while vaccines offer protection against this and other variants, their uptake remains low, with only 18 percent of adults who have received the latest vaccines. Experts said everyone should consider getting vaccinated, especially those who are over 65, immunocompromised, have health conditions that put them at higher risk of getting seriously ill or are traveling to visit loved ones who may be vulnerable.

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