Flu activity in the U.S. continues to decline after early surge

Flu activity across the United States continues to decline, though it remains at high levels in most parts of the country, the Centers for Disease Control and Prevention reported Friday in its weekly influenza update for the week ending Dec. 17.

The percentage of people seeking medical care for influenza-like illness dropped for the third straight week, and hospitalizations due to flu declined for the second week in a row. There was also a slight drop in the percentage of long-term care facilities reporting they had cases of flu among residents.

Flu activity appeared to be declining in the Southeast and Southwest, and across the northern central states.

The improving flu indicators — as well as those for respiratory syncytial virus or, RSV — suggest the country is seeing some relief after a fall when children and their parents were battered by wave after wave of respiratory illnesses.

But Caitlin Rivers, an infectious diseases epidemiologist, said it is conceivable that there could be a second peak of activity later in the winter, possibly triggered by influenza B viruses.

“We just don’t know, it’s our first go-round with this,” Rivers, a senior scholar at the Johns Hopkins Center for Health Security, said of what is the first robust flu season since the start of the Covid-19 pandemic.

The news was not all good. The CDC reported it had been advised of an additional 17 pediatric flu deaths so far this flu season, bringing the to-date total to 47. The newly reported deaths occurred over a period of seven weeks starting in early November.

This year’s pediatric death total has now surpassed that of the 2021-2022 flu season, which was 44. Both totals are substantially lower than the pediatric flu death tolls for most years prior to the Covid-19 pandemic, during which somewhere between 100 to 200 children a year were confirmed to have died from flu.

There is often a delay in the reporting of pediatric flu deaths by states and territories to the CDC, and Rivers warned that because of that, this year’s total could go up substantially in the coming weeks and months.

This year’s flu season started remarkably early. It is unusual for activity to peak — if indeed it has — before the Christmas holidays. But as respiratory bugs that were kept at bay by Covid controls early in the pandemic have started to reappear, several have done so out of season. A number that are normally fixtures of winter have instead circulated in late spring, or late summer and through the autumn.

Flu reporting years run from the beginning of October to the end of September, but flu transmission generally peaks in January or February.

To date this season, the CDC estimates there have been about 18 million influenza illnesses, roughly 190,000 hospitalizations, and 12,000 deaths from flu. Prior to the Covid pandemic, flu deaths per season in this country ranged from about 12,000 to about 55,000 in a severe season.

Virtually all of the flu activity this year has been caused by influenza A viruses; few flu B viruses have been detected here so far. The H3N2 virus has predominated, causing between 75% and 80% of illnesses, with H1N1 viruses making up the remainder.

Most of the viruses that have been sequenced to date have been well matched to the viruses in the flu shot. But it will be some weeks before the CDC will be able to estimate how protective this year’s shot was against circulating strains, the agency said.

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