ST. LOUIS — The latest statewide report on influenza shows Missouri has joined much of the country with very high levels of the virus as states battle one of the worst flu seasons in the past 15 years.

This year’s flu season started a bit late, with cases increasing around the end of December, then appearing to drop, data shows . But around mid-January, cases began to dramatically increase.

“It looked like it might have been possible it was going to be a mild flu season, but flu had something else in mind,” said Dr. Steven Lawrence, a Washington University infectious disease specialist at Barnes-Jewish Hospital. “It really came back with a vengeance and has somewhat exploded.”

In three weeks, reported cases of influenza tripled in Missouri from 5,086 reported the week ending Jan. 11, to 15,360 the week ending Feb. 1, data shows. The week ending Feb. 8, the latest data available, shows just a slight dip to 14,272 cases.

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The percentage of emergency department visits due to influenza-like illnesses is still on the rise across Missouri, going from 2% a few weeks ago to 4.6% the week ending Feb. 8.

The St. Louis County Department of Public Health said between 51 and 90 people a day sought care in emergency departments across the county for influenza-like illnesses — at times more than 5% of emergency visits — during the week ending Feb. 8.

Across the state, more than one in every three tests for flu in Missouri (35%) came back positive that week. BJC HealthCare hospitals across the St. Louis area also report a similar positivity rate.

Schools in mid-Missouri reported having to cancel classes the first week of February, and the St. Louis County health department reported a flu outbreak at a small private school where “control measures have been implemented.”

So far this season, 97 deaths from influenza have been reported in Missouri, data shows.

“It’s really to the point now where it’s the busiest, most aggressive, bad flu season since the 2009 H1N1 (swine flu) pandemic,” Lawrence said.

Nationwide, the U.S. Centers for Disease Control and Prevention estimates that there have been at least 29 million illnesses, 370,000 hospitalizations, and 16,000 deaths from flu so far this season. A total of 68 of those deaths were among children.

Flu has landed more people in the hospital in a week this season than at any time since the 2010-2011 season, according to the CDC . This flu season is now classified as a “high severity season” for all age groups — the first since 2017-2018.

Though some signs show a slight drop in transmission in the virus, Lawrence said experts need to see several weeks of dropping numbers before knowing if the worst is behind us.

“It’s a little early to know if it’s peaked yet,” he said. “We have to be careful not to jump the gun and declare that the peak is passed because, like what happened at the beginning of the year, it fooled us. We thought it was going back down, and it just popped right back up again.”

Even if the peak has passed, cases will take several weeks to return to low levels, Lawrence said. It’s not too late to get vaccinated. Experts recommend that everyone aged 6 months and older get an annual flu vaccine.

“There’s no question that we’re still going to have a lot of flu transmission and potential exposures to flu over the next month at least,” he said.

People at higher risk — such as pregnant women, and those over age 65 or with chronic health conditions — are urged to seek care within a couple days of experiencing flu symptoms in order to get prescription antiviral drugs that can help prevent severe illness.

It’s hard to pinpoint why some flu seasons are worse than others, Lawrence said. Many factors come into play, such as the weather, vaccination rates and how well-matched the circulating strains of the flu are to the vaccine.

Vaccination rates drop

Lawrence said the flu vaccine is not a good match this year, and vaccination rates have also dropped since the COVID-19 pandemic in Missouri and across the country.

CDC data shows that so far this season, 42.5% of Missouri children received their flu vaccine. That is compared to 57.2% in 2019-2020. Similar trends were seen nationwide.

Among adults ages 18 and over in Missouri, data shows 43.7% received their flu vaccine this season, compared to 47.1% last season, the only previous season available. Lawrence said numbers were usually over 50%.

Dr. Sarah George, professor of infectious diseases at St. Louis University, said people who do not see a doctor regularly tend to miss out on getting a flu shot. The focus has also been on vaccinating against COVID-19, which was killing more people than flu until just over a year ago.

“I think vaccination rates may be down slightly just because people are, if you will, ‘shotted out’ after COVID and all the boosters and what not,” George said.

Detailed flu data from the St. Louis County health department shows that the hardest-hit age group is between ages 0 to 9, with the number of cases reported in that group nearly double that of those in next hardest-hit demographic — those in their 20s.

That is typical, since children tend to spend lots of time in close contact with others in day care and classrooms, Lawrence said. “They’re very much the reservoir for which it maintains transmission in the community, and then the source of the infection for many others.”

George urged people to stay home from work if sick, and don’t send a sick child to school or day care.

“I know that’s not always easy to do when parents have to work,” she said. “But try and interrupt the chain of transmission.”

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