Not since the 2009 H1N1 swine flu pandemic has the flu burden been higher, a metric the CDC uses to estimate a season’s severity based on lab-confirmed cases, doctor visits , hospitalizations and deaths.
“It’s unusual, but we’re coming out of an unusual covid pandemic that has really affected influenza and other respiratory viruses that are circulating,” said Lynnette Brammer, an epidemiologist who leads the country’s national influenza surveillance team. CDC.
Activity is high in the southern and southeastern United States and is starting to move up the Atlantic coast.
The CDC uses a variety of metrics to track the flu, including estimating the percentage of doctor visits for flu-like illnesses. But given the similar symptoms that could include people seeking care for covid-19 or RSV, another respiratory virus with similar symptoms, laboratory data leave no doubt.
“The data is worrying,” said William Schaffner, medical director of the nonprofit National Foundation for Infectious Diseases and professor of infectious diseases at Vanderbilt University School of Medicine. “Not only is the flu early, but it also seems very serious. It’s not just a preview of upcoming attractions. We are already starting to see this film. I would say it’s a horror movie.
Adding to his concern, he said, is that the flu vaccination is behind what it usually is at this point in the season. About 128 million doses of flu vaccine have been distributed so far, up from 139 million at this point last year and 154 million the year before, according to the CDC.
“This worries me doubly” Schaffner said. The heavy flu burden “certainly looks like the start of what could be the worst flu season in 13 years.”
The number of flu cases this season is already an eighth of last season’s total estimate of 8-13 million cases.
The latest flu data comes as the country’s public health system grapples with multiple virus threats. Coronavirus cases are expected to rise as the country heads into colder weather and more people congregate indoors. New covid-19 sub-variants with a greater ability to evade immune defenses now represent 27% of casesagainst 17% a week ago. Children’s hospitals are filling up with a record number of children infected with RSV.
The effectiveness of the flu vaccine in preventing a doctor’s visit, hospitalization or death is uneven 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 well matched to the circulating strains. It provides a “little ray of sunshine” for what could be a dark 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 among humans. The seasons when H3N2 dominates usually cause the most complications, especially for the very young, the elderly and people with certain chronic conditions, experts say.
What many people don’t realize is that even after a person has recovered from the flu, the inflammatory response generated by the virus continues to wreak havoc for another four to six weeks in people of age. middle and older, increasing the rate of heart attacks. and beatings, Schaffner said.
The flu has not been a serious problem for the past two years, experts and health officials said, due to the maskingsocial distancing and other measures people have taken to protect themselves against covid-19.
Health officials tend to consider a flu season officially underway after consecutive weeks of flu activity from multiple surveillance systems, including a large percentage of doctor visits for flu-like illnesses. Those doctor visits increased for three straight weeks starting Oct. 22, more than a month earlier than in previous seasons, the CDC’s Brammer said.
The flu is notoriously difficult to predict. It’s unclear how long the season will last, how severe it will be, and whether different parts of the country will experience different levels of respiratory disease at different times. Last season, influenza activity peaked in January, “then dropped like a rock, then smoldered just below the epidemic threshold beyond March in April, May and June,” Schaffner said. This “long smoking tail was very unusual”.
“Early onset doesn’t always mean severe,” Brammer said.
In the southern hemisphere, the flu season was also very different, Brammer said. In Australia, there was “really strong, very rapid uptake and then a very rapid drop,” she said. In Argentina, the peak of influenza activity occurred during what would have been that country’s summer.
“Things haven’t returned to a normal pattern,” Brammer said.
Chile moved ahead of its poor flu season, which started months earlier than a typical season, by quickly vaccinating 88% of its high-risk population before the peak of flu activity, according to a CDC report this week. The flu vaccine used in Chile, which included a match for the dominant H3N2 virus, was about 50% effective in preventing hospitalization. The vaccine used in the northern hemisphere includes the same viral composition as the vaccine in the southern hemisphere, so experts hope the formulation could be just as effective in preventing serious flu illness.
The latest CDC data shows overall respiratory disease activity is “very high” in South Carolina and Washington, D.C. 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 the Houston Methodist Hospital System, lab-confirmed flu cases rose to 975 as of Oct. 20, from 561 the previous week, officials said.
Officials had been preparing for a more robust flu season this fall and winter because so many people have abandoned covid protective measures and are hesitant 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 infectious disease chief. But, he says, “I did not expect to see so many [flu] so early.”
Arias said conversations about flu shots have become tied to the hesitation around coronavirus vaccines. Conversations in Texas, “as you can imagine, [are] louder and at least more vocal,” he said. “We struggle with it, trying to get the message out to get vaccinated.”
People need to get a new flu shot every year to be protected, and it takes up to two weeks for the protection to kick in and the vaccine to work. The flu is contagious before symptoms appear. The CDC recommends everyone 6 months and older get a flu shot, ideally by the end of October.