US respiratory virus activity still high but continues to ebb

Markers for all three of the main respiratory viruses that are making Americans sick declined this week, and new data from the Centers for Disease Control and Prevention suggest that the current flu season has been moderate so far and that people with chronic conditions continue to make up the bulk of flu hospitalizations.

In its respiratory virus snapshot, the CDC said activity is still elevated but decreasing across most of the country. More specifically, flu and COVID-19 activity are stabilizing or decreasing, and respiratory syncytial virus (RSV) infections continue to decline.

Moderate flu season so far

Most flu markers, including outpatient visits for flulike illness, declined for the third week in a row, and the percentage of respiratory specimens that were positive for flu held steady, at 14.2%, the CDC said in its latest weekly FluView report today. Influenza A is still dominant, and subtype sampling shows that the 2009 H1N1 virus remains the dominant strain.

Southern states are still reporting the highest activity, followed by the Northeast and Southwest.

Though deaths from flu trended downward overall, the CDC reported 10 more pediatric flu deaths, raising the season’s total to 57. The fatalities were reported between the week ending December 23 and the week ending January 13. Six involved influenza A, and three involved influenza B. Of subtyped influenza A viruses, all were 2009 H1N1.

One of the children who died was coinfected with 2009 H1N1 and influenza B.

In separate data updates, the CDC today posted a preliminary severity estimate for the current flu season, which it listed as moderate across all age-groups. The CDC included the caveat that the classification could change as the season progresses, and in other updates it said a second peak in activity sometimes occurs after the winter holidays.

Also, the CDC today released a deeper dive into flu hospitalizations, which show that people with chronic health conditions continue to make up the lion’s share of hospital cases.

For adults, the most common underlying conditions for those hospitalized for flu were high blood pressure, cardiovascular disease, metabolic disease, and obesity. For children, the most common chronic conditions for asthma, obesity, and neurologic disease. However, 31.1% of children hospitalized for flu had no known underlying health conditions.

COVID wastewater levels high, but declining

In the CDC’s COVID-19 data updates, severity and early indicators all showed declines, including deaths, which had trended upward in its previous update. Activity remains elevated, however.

Emergency department visits for COVID are highest in highest in infants and older adults, but are also elevated among young children.

The CDC’s wastewater surveillance system dashboard shows that SARS-CoV-2 detections are still listed as very high, but have declined steadily since the start of the new year. Biobot wastewater tracking shows that detections are highest in the Northeast, followed by the Midwest. However, levels are declining for all parts of the country.

Despite continued high wastewater levels, COVID infections appear to be causing less severe disease than earlier in the pandemic. Hospital bed occupancy and intensive care unit capacity for all patients remains stable nationally, the CDC said.

CDC reminder about RSV seasonality

RSV indicators continue to decline in some areas, and though hospitalizations are decreasing among children, they remain elevated in older adults.

In new developments, the CDC today sent a Clinician Outreach and Communication Activity (COCA) Now message to clinicians, reminding them of seasonal differences in its recommendation regarding RSV (Abrysvo) vaccination for pregnant women during 32 to 36 weeks gestation.

In most of the continental United States, the RSV vaccine should be given to the group from September 1 through January 31 to get the most protective effect for babies born during increased RSV activity.

However, RSV seasonality varies in some parts of the nation, including Alaska, southern Florida, Guam, Hawaii, Puerto Rico, the US Pacific Island territories, and the US Virgin Islands. The CDC said health practitioners in those areas may consider RSV vaccination of pregnant women after January 31.

“Infants born to unvaccinated mothers should receive nirsevimab, a long-acting monoclonal antibody that provides immediate protection to the infant against RSV-associated LRTD [lower respiratory tract disease],” the CDC said.

Uptake of RSV preventive drug

In another development this week, the CDC added nirsevimab (Beyfortus) coverage to its RSV vaccine coverage dashboard, which indicates that, as of December 2023, 28.7% of women who had an infant younger than 8 months said their babies had received the injection.

The new monoclonal antibody is designed to protect newborns against RSV and was in short supply this fall after demand exceeded manufacturer expectations.

Another 31.4% said they plan to get nirsevimab for their babies, and 33.9% who are currently pregnant say they their newborns will definitely receive it. Of women trying to get pregnant, 44.2% say they plan to have their babies get the drug.