Respiratory virus season in the US isn’t over yet

After a few weeks of decline, some measures show that flu activity is starting to pick up again and respiratory virus levels remain high overall in the United States.

During the week ending January 27, more than 82,000 people who visited an emergency department were diagnosed with influenza, according to data from the US Centers for Disease Control and Prevention — an 8% bump, or about 6,000 more than the week before. The test positivity rate for flu also ticked up in the US overall.

A second surge of flu activity after the winter holidays is common, but experts say it’s notoriously difficult to predict exactly how long or how severe the full season will be. Sometimes this surge is the start of a full second wave, but it could also be a minor blip before a more consistent decrease, the CDC says.

A traditional second wave of influenza usually comes after a more significant downturn, when influenza B viruses start to overtake influenza A viruses that were predominantly circulating, said Alicia Budd, who leads domestic flu surveillance for the CDC.

There’s no evidence of that happening yet, but it’s too early to rule anything out, she said.

“We’re still at the midpoint of the season,” Budd said. “It’s too early to tell exactly where we are in our ultimate trajectory. We just don’t know yet. But we are still seeing a lot of activity right now.”

Covid-19 and RSV also continue to circulate at high levels. Emergency department visits for Covid-19 and RSV have been declining for a month, but there were still more than 50,000 emergency department visits and about 23,000 hospitalizations for Covid-19 during the week ending January 27, CDC data shows.

The downward trend for Covid-19 is coming as expected, and the peak for flu may be shifting a bit later this season, said Dr. Michael Mina, an epidemiologist and chief science officer of eMed, a telehealth company focused on at-home testing.

“It’s not so much that flu is now replacing Covid, it’s just like: Covid did its thing and now it’s coming down,” he said. “(Covid is) doing exactly the identical thing as it’s done, and in this case, we just have a flu season that shifted a little bit to the right. Flu shifts by orders of months actually from year to year. Covid is a little bit more consistent.”

While national trends are helpful, expert say that local trends are the best way to gauge risk and make decisions about how to stay safe and healthy.

Overall, 18 states and Washington, DC, are still experiencing high or very high levels of respiratory illness, according to the CDC. New data from the CDC’s Center for Forecasting Analytics suggests that flu infections are growing in four states — Florida, New York, Oklahoma and Texas — and likely growing in five others: Arkansas, Kentucky, Massachusetts, North Carolina and South Carolina. Wastewater surveillance suggests that Covid-19 levels are highest in the South, with forecasted case increases in South Carolina, in particular.

Experts say that trends in the US have stayed within expected ranges so far this respiratory virus season. But the burden of disease is still very high. The CDC estimates that there have been at least 20 million illnesses, 230,000 hospitalizations and 14,000 deaths from flu so far this season.

“It’s normal in terms of the amount of activity but it is a very, very high burden,” Budd said.

There is early data to suggest that the latest Covid-19 vaccine and this year’s flu shot offer strong protection this season, and experts say it’s still not too late to get vaccinated. They also urge the public to practice etiquette — hand washing, covering coughs and sneezes, staying home when sick — to avoid unnecessary spread.

“That’s how we can help each other,” Budd said.

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