Not since the 2009 H1N1 swine flu pandemic has there been such a high burden of influenza, a metric the CDC uses to assess the severity of a season based on laboratory-confirmed cases, doctor visits, hospitalizations and deaths.
“It’s unusual, but we’re coming off an unusual Covid pandemic that has really affected influenza and other respiratory viruses that are circulating,” said Lynette Brammer, an epidemiologist who leads the CDC’s domestic influenza surveillance team.
Activity is high in the southern and southeastern US and is beginning to move up the Atlantic coast.
The CDC uses a variety of measures to track influenza, including estimating the rate of doctor visits for influenza-like illness. But given the similar symptoms that could include people seeking care for covid-19 or RSV, another respiratory virus with similar symptoms, the lab data leaves little doubt.
“The data is ominous,” said William Schaffner, medical director of the nonprofit National Foundation for Infectious Diseases and professor of infectious diseases at Vanderbilt University School of Medicine. “The flu is not only injured, but it seems very severe. This is not just an overview of upcoming attractions. We are already starting to watch this movie. I would call it a scary movie.”
He said he adds to his concern that flu vaccinations are lagging behind usual at this point in the season. About 128 million flu vaccine doses have been given out so far, compared with 139 million at this time last year and 154 million the year before, according to the CDC.
“It makes me doubly worried” Schaffner said. The high flu burden “certainly looks like the start of the worst flu season in 13 years.”
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The number of flu cases this season is already one-eighth of last season’s total estimate of 8 to 13 million cases.
The latest flu data comes as the nation’s strained public health system grapples with multiple viral threats. Cases of the coronavirus are expected to increase as the country heads into colder weather and more people huddle indoors. New sub-variants of covid-19 with a greater ability to evade immune defenses now account for 27 percent of cases, up from 17 percent a week ago. Children’s hospitals are filling up with a record number of children infected with RSV.
The flu vaccine’s effectiveness in preventing a doctor’s visit, hospitalization or death varies from year to year, and in recent years has hovered between 40 and 60 percent, according to the CDC. But Brammer and others say this season’s vaccine is adequate against circulating strains. It offers “a little ray of sunshine” for what could be a bleak winter, Schaffner said.
Nationally, the predominant virus — a particularly nasty strain, H3N2 — is causing the worst outbreaks of the two types of influenza A viruses and two influenza B viruses that circulate in humans. Seasons in which H3N2 dominates tend to result in the most complications, especially among the very young, the elderly and people with certain chronic health conditions, experts say.
What many people don’t realize is that even after someone recovers from the flu, the inflammatory response generated by the virus continues to wreak havoc for another four to six weeks in the middle-aged and older, increasing the incidence of heart attacks and strokes, Schaffner said.
The flu has not been a major problem in the past two years, experts and health officials said, because of the masking, social distancing and other measures people have taken to protect themselves from covid-19.
Health officials tend to consider flu season officially underway after consecutive weeks of flu activity from several surveillance systems, including a significant percentage of doctor’s office visits for flu-like illnesses. Those doctor visits have increased for three straight weeks since Oct. 22, more than a month earlier than previous seasons, the CDC’s Brammer said.
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The flu is notoriously difficult to predict. It is difficult to know how long the season will last, how severe it may be, and whether different parts of the country will experience different levels of respiratory illness at different times. Last season, flu activity peaked in January, “then dropped like a rock, then smoldered just below the epidemic threshold after March through April, May and June,” Schaffner said. This “long smoldering tail was very unusual.”
“Early doesn’t always mean serious,” Brammer said.
In the southern hemisphere, flu season is also far different, Brammer said. In Australia, there was “a really sharp, very rapid uptake, then a very rapid decline”, she said. In Argentina, the peak of influenza activity occurred during the summer, which would be in this country.
“Things have not returned to a normal pattern,” Brammer said.
Chile got ahead of its bad flu season, which started months earlier than the typical season, by quickly vaccinating 88 percent of its high-risk population before flu activity peaked, according to a CDC report this week. The flu vaccine used in Chile, which includes a match of the dominant H3N2 virus, is about 50 percent effective in preventing hospitalization. The shot used in the Northern Hemisphere includes the same virus composition as the vaccine for the Southern Hemisphere, so experts hope the formulation may be just as effective at preventing severe flu illness.
The latest CDC data shows overall respiratory disease activity is “very high” in South Carolina and the District of Columbia and “high” in 11 states: Alabama, Georgia, Louisiana, Maryland, Mississippi, New Jersey, New York, North Carolina, Tennessee, Texas and Virginia.
Texas was among the first states to see flu activity in late September. At Houston Methodist Hospital System, laboratory-confirmed flu cases rose to 975 as of Oct. 20, up from 561 the previous week, officials said.
Officials have been bracing for a stronger flu season this fall and winter because so many people have abandoned Covid protection measures and are unwilling to get vaccinated.
“It was something we expected because we’re a hub and a lot of people travel here,” said Cesar Arias, the hospital system’s chief of infectious diseases. But he said: “I didn’t expect to see so much [flu] so early.”
Arias said the conversation surrounding flu vaccinations has become intertwined with the hesitancy surrounding coronavirus vaccines. Conversations in Texas, “as you can imagine, [are] stronger and at least more vocal,” he said. “We’re fighting that, trying to get the message out to get vaccinated.”
People must get a new flu shot each year to be protected, and it takes up to two weeks for protection to start and for the vaccine to work. The flu is contagious before symptoms appear. The CDC recommends that everyone 6 months and older get a flu shot, ideally by the end of October.