Colorado’s flu season is off to an early start, and mutations in one version of the virus are raising concerns among experts that more people than usual will get sick this year.
The state has higher rates of flu hospitalizations, emergency room visits and positive tests than it did at this time last year, state epidemiologist Dr. Rachel Herlihy said. People who haven’t gotten their flu shots should do so now, particularly since it takes two weeks to develop full immunity after vaccination, she said.
“The virus is absolutely here,” she said.
At this point, COVID-19 and respiratory syncytial virus activity is still low, Herlihy said. Viruses often peak at different times, which is good for the health care system because it limits the number of people getting sick at once, she said.
Other countries have also had an early start to the flu season, but experts are waiting for further data from overseas before projecting if the virus will peak early, Herlihy said. Even if it does, though, the season often includes a long tail following the peak, or a second wave with a different virus subtype, she said.
“When we reach the peak, the best-case scenario is we’re halfway through the season,” she said.
The number and demographics of people who need hospital care for respiratory viruses doesn’t look unusual as of early December, said Dr. Michelle Barron, senior medical director of infection prevention and control for UCHealth. The Southern Hemisphere did have a more-severe flu season over what we experience as summer, however, she said.
“So far, the numbers don’t look out of the ordinary, but we’re at the beginning,” she said.
National experts have warned that this flu season could be severe, though not enough data has come in to know for certain. A flu subtype called H3N2 picked up seven mutations since last respiratory season. Countries have surveillance systems to look for any new mutations in flu viruses, though most end up being unimportant, said May Chu, an epidemiologist at the Colorado School of Public Health.
“We have to remain alert,” she said.
The early data from the United Kingdom and Japan suggest this flu season could be severe again, because immune systems haven’t encountered the variant known as subclade K before and it arrived too late to include in this year’s shots, Dr. Tom Frieden, director of the Centers for Disease Control and Prevention from 2009 to 2017, said in a news conference. But the shot is still worth getting, even with imperfect protection, he said.
“That’s a lot better than nothing, and it’s the best thing you can do,” he said.
Last season was the most severe for children since the 2009 swine flu pandemic. The CDC determined 279 children died of flu complications and children’s hospitals reported unusual neurological complications in kids, most of whom were unvaccinated. The government doesn’t track adult flu deaths precisely, but produced a broad estimate of somewhere between 38,000 and 99,000 in the most recent season.
The data doesn’t yet show whether subclade K is more severe than other types of H3N2, Herlihy said. It wouldn’t have to be to cause a severe season, however – if more people get the flu, the number of severe cases and deaths also will rise, even without a change in virulence, she said.
“Some of this is a numbers game,” she said.
Despite the mutated variant, early data from the U.K. suggests the vaccine is between 30% and 40% effective in preventing hospitalization in adults and about 70% effective in children. That suggests vaccine effectiveness is on the lower end of the normal range, Herlihy said.
About 25% of eligible Coloradans have received a flu vaccine this year, compared to 27% at the same time last year. The drop was sharper for COVID-19, from about 14% to 11%. Anyone 6 months or older who doesn’t have a medical contraindication, such as a severe allergy to the vaccine ingredients, can get both shots.
Nationwide, vaccination rates also appear to be down. IQVIA, a health data company, estimated pharmacies and long-term care facilities provided about 27% fewer COVID-19 shots between early August and mid-November than they did during the same period last year. Flu shots dropped more modestly, by 6%.
“These numbers aren’t just statistics. They represent real gaps in protection,” Dr. Bob Hopkins Jr., medical director of the National Foundation for Infectious Diseases, said during a news conference Wednesday.
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