With hospitalizations ticking up, flu season appears off to an early start

There are increasing signs that flu season is off to a very early start in parts of the United States, with the cumulative hospitalization rate higher than it has been at this point in the fall for more than a decade, the Centers for Disease Control and Prevention reported Friday.

In its weekly FluView report, the CDC estimated that there have already been 880,000 influenza illnesses, 6,900 flu hospitalizations, and 360 deaths caused by flu this season, which started at the beginning of October. It is unusual for the CDC to have enough data to issue estimates on the burden of flu this early in the season. 

These figures are estimates, based on data from a flu hospitalization surveillance network of acute care hospitals in 14 states. Flu activity is currently highest in south-central and southeast parts of the country, and New York. It is also picking up along the Eastern Seaboard.

The CDC also reported the death of a child, the first pediatric flu death of the new flu season. It occurred in the week ending Oct. 8. 

In the first two winters of the Covid-19 pandemic, the new coronavirus and the measures people took to protect themselves from it suppressed transmission of a number of respiratory pathogens that normally make the rounds. That hiatus has ended and those viruses are returning, though often at times when they didn’t normally circulate in the past. Hospitals around the country are seeing record numbers of cases of respiratory syncytial virus, or RSV, right now. In pre-Covid times, RSV didn’t typically emerge until the winter.

Some people are interpreting the early start of flu activity as evidence we are in for a harsh flu season. But Lynnette Brammer, team lead for domestic surveillance in the CDC’s influenza division, said it’s impossible at this point to know how bad the season will be.

“What a lot of people are implying is because it’s early and levels are high for this time of year that it’s going to be a severe season. We don’t know that,” Brammer told STAT.  “Right now all we can say is we’re off to an early start.” 

She noted that people who have been waiting to get a flu shot to try to time it to the start of flu circulation should not hold off any longer. “You need to get vaccinated now, if you haven’t already done that.”

Ed Belongia, director of the Center for Clinical Epidemiology and Population Health at Wisconsin’s Marshfield Clinic Research Institute, said there is good reason to be worried that this could be a severe flu season. Most immune systems haven’t seen flu viruses for a couple of years, which means the pool of people susceptible to infection is large. And the measures society took to try to slow spread of Covid — mask-wearing, social distancing, school closures — have mostly been abandoned. 

But Belongia has been studying flu for too long to guess how a flu season will unfold. The virus is maddeningly unpredictable.

“Whether or not the whole season is going to be longer and more severe, we really just don’t know at this point. It’s too early to say,” he said.

Evidence from the Southern Hemisphere’s flu season — which sometimes provides hints of what’s in store for us — showed oddly timed and active flu seasons, but not necessarily bad ones. Australia had a lot of flu activity, mainly in children. But a report on its 2022 winter season issued earlier this month stated that the clinical severity of the season, based on the numbers of intensive care admissions and deaths, was actually low. It rated the overall impact of the flu season as low to moderate.

Other hopeful news from the Southern Hemisphere was that the flu vaccine seems well-matched to the viruses that are circulating. A report this week from Chile in the CDC’s online journal Morbidity and Mortality Weekly Report estimated flu vaccine efficacy at 49% against H3N2 viruses, the subtype that caused most of the disease there. It is also the virus currently causing most disease in the U.S.

Belongia said he was pleasantly surprised, adding  “49% is about as good as you can expect to see for H3N2. So I thought that was encouraging.”

While it’s impossible to guess how bad the flu season will be, there is one thing that does look reasonable to assume. If the current levels of circulation of influenza and RSV virus continue or increase, there could be a lot of respiratory illness around Thanksgiving. Much of the current illness is in young children, who typically get sick first in the cold and flu season and spread their bugs to siblings, parents, grandparents, and other adults with whom they are in contact.