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Infl uenza Rates Head Downward in Early 2022 Flu Season Appears Less Severe Than Anticipated
BY NEAL LEARNER
Contrary to some projections, cases of seasonal influenza peaked at the end of last year and started to decline in early 2022. Some experts had expected a more robust 20212022 flu season in the United States, as COVID-19 pandemic restrictions eased and students headed back to the classrooms.
But data so far have not borne that out.
Overall, influenza activity has decreased in recent weeks, while sporadic activity continues across the country, and some areas are seeing an increase, the CDC said in its March 18 influenza surveillance report.
As of March 12, the CDC estimates 2.9 million flulike illnesses, 28,000 hospitalizations and 1,700 deaths due to influenza this season, with influenza A(H3N2) being the dominant strain. Thirteen deaths were in children, more than last year, but well below pre-COVID seasons.
Accompanying the decline in cases was a drop in the percentage of outpatient visits due to respiratory illnesses. Those cases are now below baseline, the agency added.
The overall cumulative hospitalization rate this season is 4.4 per 100,000 population. While higher than last year, the current rate is significantly lower than pre–COVID-19 levels. The hospitalization rates ranged from 16.9 to 51.4 per 100,000 people during the seasons from 2016-2017 through 2019-2020, the CDC noted.
By Feb. 12, 3% of specimens submitted to clinical laboratories were positive after peaking at 6% earlier in the season, according to Lisa Grohskopf, MD, MPH, of the CDC’s Influenza Division, who updated the Advisory Committee on Immunization Practices (ACIP) on Feb. 23. Most specimens that were subtyped were H3N2 viruses, she added, and so far these viruses are “genetically closely related to the vaccine virus, but there are some antigenic differences that have developed as H3N2 viruses continue to evolve,” she explained.
The number of B/Victoria viruses is low, and they are antigenically similar to the vaccine.
The cumulative hospitalization rate (FluSurv-NET) is higher than that for the entire 2020-2021 season, but lower than that observed at this time during the four seasons preceding the pandemic, she added.
The ACIP is reviewing the approved enhanced seasonal influenza vaccines to decide whether to make a recommendation for adults who are 65 years of age and older. At the meeting, the panel acknowledged the benefits of an enhanced influenza vaccine compared with standard egg-based flu shots. Three vaccines are being reviewed: Fluad Quadrivalent (Seqirus), Fluzone (Sanofi Pasteur) and Flublok Quadrivalent (Protein Sciences Corp.).
“According to the CDC, older adults have an increased risk of influenza-related complications and severe outcomes. Data from the recent ACIP systematic review support the benefit of an enhanced influenza vaccine for this population,” said Gregg Sylvester, the chief medical officer of Seqirus.
Did COVID-19 Mitigation Help?
The numbers are heading in a positive direction, even if the reason isn’t exactly clear. What first looked to be a “moderate or moderately severe” influenza season may be tapering off,
said William Schaffner, MD, a professor of infectious diseases at Vanderbilt University Medical Center, in Nashville, Tenn.
While encouraged by the trend, he also cautioned that cases often rise through February and March, and no one is entirely sure what the influx of refugees from the Ukraine will add to the global mix (see cover story on page 10). “Flu is fickle, and we could have a second wave,” Dr. Schaffner noted.
Dr. Schaffner acknowledged that he cannot explain why flu rates are trending downward, especially as people are out and about and children are in school. But it probably is related to some of the mitigation strategies, which were just lifted.
“There’s still a substantial amount of mask-wearing, and g that may have an impact on what we’re seeing,” he speculated.
Such reports are good, if somewhat counterintuitive, based on earlier projections. Because there was so few flu cases last season, influenza experts had postulated the possibility that our collective influenza immunity might have waned, Dr. Schaffner said.
“In this case, we might have anticipated a brisker influenza season with more severe disease,” he said.
Other experts see additional COVID-19 factors influencing this year’s flu season.
Influenza likely is milder due to the circulating SARS-CoV-2 omicron variant, which may be competing with the current A(H3N2) strain, postulated Paul G. Auwaerter, MD, a clinical director in the Division of Infectious Diseases at the Johns Hopkins University School of Medicine, in Baltimore.
Each year, public health officials urge people to get their flu shots. That message may have gotten lost this year in the ongoing focus on COVID-19 vaccinations and boosters.
Flu vaccination coverage among children, for example, is lower than last season, Dr. Auwaerter said. Vaccination rates among adults vary depending on the state, he added.
Dr. Schaffner attributed the lower flu vaccination rates to two things: 1. general vaccine fatigue and 2. everyone’s preoccupation with COVID-19 versus influenza.
“As I’ve been out there beating the drums trying to stimulate interest in vaccinations against flu, I’ve almost had to reintroduce people to flu, and say, ‘Remember there’s another nasty respiratory virus out there,’” Dr. Schaffner said. “And it’s a bit like, ‘Oh, yeah, I remember that.’ It’s not entirely surprising that vaccination rates have lagged behind what we might have expected at this time of year.”
Drs. Schaffner and Auwaerter stressed the importance of receiving the vaccine, even if the H3N2 vaccine component is a bit off target against the current strain. “It’s not a tight match,” Dr. Schaffner said. “But—and this is hugely important—even when we’re not exactly on target with the vaccine, vaccination still provides notable protection against severe disease. You’re less likely to require admission to the hospital, less likely to have to go to intensive care unit and less likely to die. That’s part of the story that often gets lost.” Dr. Auwaerter also underscored the vaccine’s protection against the less dominate influenza B strain: “Getting an influenza vaccine is still helpful in people to help reduce the likelihood of infection, especially as influenza ter- B tends to occur later in the winter or early e spring—and flu shots help lessen the chances of progressing to severe infection, even with a mismatch.”
Coinfections With COVID-19
The burning question on everyone’s mind is the possibility of influenza/COVID-19 coinfection, and whether that might predisac- pose patients to more serious disease of one kind or another. So far, there hasn’t been an avalanche of reports, but the season is not yet over, Dr. Schaffner reminded. “We have to wait for this to play out.” In the meantime, providers are busy testing their patients with respiratory illnesses to determine whether they might have influenza or COVID-19. Distinguishing between infections will determine the course of treatment, Dr. Schaffner said. Physicians have new monoclonal antibodies and antivirals to prevent mild COVID-19 from progressing to something more serious. They also have long available antivirals to treat influenza. “If you’re going to provide treatment, you really have to distinguish [between] the two infections,” he said.
Future Influenza Seasons
Going forward, Dr. Schaffner expects to see more routine public health recommendations during flu season to wear masks, maintain social distancing and even rent a movie rather than go to a theater. “A lot of people have learned those lessons, so they’ll start doing that on their own,” he predicted. “People no longer think you’re crazy if you’re out there wearing a mask.” ■ The sources reported no relevant financial conflicts of interest.
