Flu activity spiked in cases with no spike after the holidays, but the respiratory virus season is still in full swing


Flu remains prevalent in the US, but the first wave of the season – which swept through the country weeks earlier than usual – appears to have peaked.

The weeks following the year-end holiday brought continued high levels of transmission and hospitalization, but flu activity appears not to have picked up, as many public health experts warned.

Still, data released Friday by the U.S. Centers for Disease Control and Prevention, even after weeks of improvement, shows that more than 12,400 people were hospitalized for the flu in the first week of the new year, and nearly 9% of the lab tests were positive for flu.

About 4% of everyone who visited a healthcare provider last week had symptoms of the respiratory virus, including fever plus a cough or sore throat, which is nearly twice the national baseline.

Influenza is notoriously unpredictable and a season can bring multiple peaks of activity.

“It’s pretty clear that there was a spike in activity, but that doesn’t mean we won’t have another one,” Lynnette Brammer, chief of the CDC’s domestic flu surveillance team, said last week. “Things can turn around and go back up.”

Flu vaccination rates remain well below ideal levels and hospitals remain very full, leaving the US vulnerable as the respiratory virus season continues.

“It is definitely something we are going to look at very closely. We just need to keep an eye on all the data, see what viruses are circulating and who is getting sick, and what impact that has,” Brammer said.

“And I want to remind people that if they haven’t already gotten vaccinated, please do so. It’s not too late.”

As of Dec. 31, about 171 million doses of flu vaccine had been distributed in the US — enough to cover only about half of the population. According to CDC data, only 40% of adults had received the shot by the end of November, and only 48% of children had received the shot by the end of December.

Through Jan. 7, the CDC estimates there have been 24 million illnesses, 260,000 hospitalizations, and 16,000 deaths from the flu this season.

Although this season hit earlier than usual, the results are within an expected range – at least so far.

“It is not an unusually high flu season. It’s more or less in the mid to upper range, but it’s unfortunately within the bounds of what we normally expect to see during a regular flu season,” Brammer said. “So basically this looks like a typical flu season, except for the timing. It was just a little earlier than usual.”

Overall, activity of flu and other respiratory viruses remains “high” or “very high” in about half of the states, according to the new CDC data, and the U.S. continues to contend with multiple respiratory viruses circulating at high levels.

RSV activity also peaked in the US, peaking in mid-November for the season. But even after a steep trend decline over the past month and a half, weekly RSV hospitalizations remain higher than the peaks of the most recent seasons.

RSV is particularly dangerous for children, and at least 13 of every 100,000 children under age 5 were hospitalized for RSV in the last week of the year, bringing the cumulative number of hospitalizations this season to 5 of every 1,000 children in this age group coming .

Meanwhile, Covid-19 activity has been on an upward trend in recent months.

Hospital admissions have been on the rise since November and have surpassed the most recent peak this summer, before the updated booster shot was available, federal data shows.

Case reporting has become more erratic over the course of the pandemic, but wastewater monitoring data from Biobot Analytics suggests Covid-19 activity is also higher than during the Delta wave.

The fast-growing Omicron subvariant XBB.1.5 is now responsible for an estimated 43% of new Covid-19 cases in the US, according to the CDC, making it the strain that causes the most new infections in the US.

Notably, it is the only variant gaining ground in the US

XBB.1.5 was first detected in New York in October. It grew rapidly in the Northeast and the CDC estimates it is responsible for more than 80% of new cases in that region.

From there, XBB.1.5 seems to be picking up steam along the East Coast. It now accounts for about half of Covid-19 cases in the mid-Atlantic states and nearly a third of cases in the Southeast. It is less common in other US regions.

The emergence of XBB.1.5 coincided with an increase in Covid-19 hospitalizations, especially among seniors.

XBB.1.5 has an important mutation that allows it to bind more tightly to cells. Experts believe this may help make it more contagious.

Yet only 16% of the US population has received their updated Covid-19 booster shot. Data from October shows that people aged 5 and older who received an updated booster were 19 times less likely to die from Covid-19 compared to those who were not vaccinated. The chance of testing positive was three times lower for those who had their updated booster.

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