US COVID activity jumps as JN.1 expands, brisk flu and RSV levels continue

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The proportion of JN.1 Omicron subvariant detections jumped dramatically last week, which could supercharge a rise in COVID-19 activity as the United States approaches its winter holiday weeks, according to updates today from the Centers for Disease Control and Prevention (CDC).

Also, the CDC today reported more steady rises in flu activity, especially in the Southeast and South-Central regions, as respiratory syncytial virus (RSV) activity across the nation remains elevated.

In a video message posted on Twitter earlier this week, CDC Director Mandy Cohen, MD, MPH, said it's not too late to be vaccinated against the three respiratory viruses for those who haven't already, and she urged people to take additional measures like avoiding sick people, washing hands, improving ventilation, and wearing a mask.

CDC singles out JN.1 for tracking

JN.1 is proving to be the fastest-growing member of the BA.2.86 family, and variant trackers have projected that it could trigger the next COVID surges. Some countries in Europe have already reported sharp JN.1 spikes.

Today in its latest variant proportion update, the CDC singled out JN.1 from under the BA.2.86 umbrella, showing that over the last 2 weeks, the JN.1 level jumped from 8.1% to 21.4%. Also, JN.1 is now the second-most commonly detected variant, led only by HV.1, which is part of the XBB.1.9.2 lineage.

In a separate update on JN.1 today, the CDC said the continued growth of JN.1 suggests it is either more transmissible or better at evading the immune system. However, it added that there's no evidence that it poses an increased risk compared to other variants.

The CDC said it's not known to what extent JN.1 is contributing to increases under way in December but said COVID activity is likely to increase over the next month and that lab data suggest the updated COVID vaccine protects against JN.1 and other variants.

COVID markers show growing momentum

Meanwhile, the CDC's two severity indicators for COVID—hospitalizations and deaths—both showed notable rises over the past week, with hospitalizations up 17.6% and deaths up 25% compared to the week before, still at a lower rate than the CDC saw in November 2022. For hospitalizations, moderate levels were reported, mostly in the Midwest and Mid-Atlantic regions, with pockets in parts of some states at the high level, such as Montana, South Dakota, and West Virginia.

For deaths, states reporting some of the biggest increases last week included Alabama, Maine, Maryland, Minnesota, Missouri, and West Virginia. In its weekly respiratory virus snapshot, the CDC said COVID-19 is still the main driver of viral respiratory deaths.

The CDC's early indicators also showed rises, with test positivity up 0.9% and emergency department visits up 4%. Test positivity was higher in the Midwest, Mountain West, and Northeast than in other parts of the country. And of ED visits for COVID, infants and seniors had the highest levels, with levels also elevated for young children.

Wastewater SARS-CoV-2 tracking, another early indicator, continued to show high levels, especially in the Midwest.

Flu continues to expand

As health systems brace for more COVID activity, seasonal flu activity continues to rise in most areas, with all 10 regions either at or above their baselines for flulike illness outpatient visits, the CDC said today in its weekly flu update. Virus testing at public health labs shows that influenza A makes up 80% of positive samples, and of subtyped viruses, 2009 H1N1 is still dominant, at 74.1%.

Flu hospitalizations are still low but are rising, with the highest levels in seniors, followed by adults ages 50 to 64 and children ages 4 and younger.

Four more pediatric flu deaths were reported last week, raising the season's total to 12. All occurred in November, three involving H1N1 and one due to influenza B.

RSV hospitalizations rising in older adults

For RSV, hospitalizations remain elevated in children but are on the rise in older adults, the CDC said in its weekly respiratory virus snapshot. It noted that only 15.9% of adults who are eligible to be vaccinated against RSV had been immunized.

Overall, though, RSV hospitalizations are down a bit, as is test positivity for the virus.

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