Here's Why This Year's Flu Season Is the Worst in Over a Decade

Flu activity is continuing to ramp up across the United States, resulting in the highest number of positive flu tests and hospitalizations in more than a decade, according to the Centers for Disease Control and Prevention (CDC).

As of December 9, the CDC estimates there have been at least 13 million illnesses, 120,000 hospitalizations, and 7,300 deaths (including at least 21 children) so far this flu season.

CDC data also shows that 46 states are experiencing “high” or “very high” levels of influenza-like illness (ILI) activity—which factors in not just flu cases, but also other illnesses like respiratory syncytial virus (RSV) and COVID-19.

“At this point, we are looking at one of the worst flu seasons since the 2009 H1N1 swine flu pandemic,” Robert Glatter, MD, emergency room physician at Lenox Hill Hospital, told Verywell. “The high burden of flu this early in the season has easily surpassed what we have typically seen in the past 13 years.”

Experts suggest there are three main factors contributing to this year's flu severity: the dominance of an influenza A strain, low flu vaccination rates, and loosened COVID restrictions.

This Year's Strain Is Particularly Severe

During the 2009-2010 flu season, there was an early start and a rapid rise in the number of cases, similar to this year’s flu season. However, the 2009-2010 flu season was different from the current flu season because a new or novel flu strain, called H1N1, had emerged.

“A separate flu vaccine was made to target this strain [H1N1],” Shanthi Kappagoda, MD, a board-certified infectious disease physician and clinical associate professor of medicine and infectious diseases at the Stanford School of Medicine, told Verywell. “The current flu season is not being driven by a virus strain we have not seen before and the predominant strains that are circulating are included in this season’s flu vaccine.”

Even though there is no new flu strain spreading, most of the viruses circulating right now are influenza A. According to CDC data, of the influenza A viruses detected this season, 76% have been influenza A (H3N2) viruses, and 24% have been influenza A (H1N1) viruses.

“Usually, H3N2 viruses are associated with more severe seasons—especially among the very young and older adults,” Michael Jhung, MD, MPH, associate director for epidemiologic science in CDC’s Influenza Division, told Verywell.

Type A strains have been associated with more severe disease, hospitalizations, and deaths. Glatter said this is because influenza A viruses are the “only viruses known to cause flu pandemics” and can spread efficiently among people particularly if they have little or no immunity.

Low Vaccination Rates Make Flu Worse

According to Glatter, current flu vaccination rates in the U.S. could be another reason why there’s been early and high numbers of flu cases, hospitalizations, and deaths. 

A 2022 National Survey from the National Foundation for Infectious Diseases (NFID) found 41% of adults say they are either unsure or do not plan to get vaccinated against the flu during the 2022-2023 flu season because they have concerns that the vaccines don’t work very well and will have side effects. 

The survey also showed that one in five Americans who are at higher risk for flu-related complications said they were not planning to get vaccinated this flu season. 

"The lack of adequate flu vaccination in the U.S. thus far—spurred by anti-vaccination sentiments and misinformation related to mRNA vaccines—combined with poor adherence to masking, has accounted for the early numbers," Glatter said,

Loosened COVID Restrictions Exacerbated the Flu's Rebound

During the COVID-19 pandemic, many people followed precautions—such as masking, frequent hand washing, and avoiding large gatherings—that not only helped prevent the spread of COVID but also other infectious illnesses like the flu.

“The measures we took to avoid COVID-19 resulted in a marked decrease in flu cases,” Kappagoda said. “That means that fewer people were exposed to and developed natural immunity to the flu.”

However, experts say that the lifting of mask mandates, changes in societal behaviors, and the public’s increasing reluctance to get vaccinated and general exhaustion with COVID precautions are likely playing a role in the large rebound in flu case numbers we’re seeing so far this year.

“The flu has not been a major issue for the last two years due to adherence to wearing masks, social distancing, people working from home, and attending fewer social gatherings in large indoor venues,” Glatter said. “Certainly societal behaviors can have an impact on how quickly the flu spreads from a population standpoint.”

Has This Year’s Flu Season Already Peaked?

The CDC classified the severity of last year’s flu season (2021-2022) as low, and Kappagoda pointed out there were only 5,000 deaths due to the flu in the 2021-2022 flu season. In a typical flu season, there are about 25,000 to 50,000 deaths.

"Flu season started early this year and it has not peaked yet," Kappagoda said. "We have not seen our flu cases or hospitalizations peak yet, so I think, yes, there will be more cases before they start to decline.”

Since flu illnesses, hospitalizations and deaths are already so high this early in the season and are close to the overall numbers from the previous year, Glatter believes the current flu season may get worse and be more prolonged than typical flu seasons.

“It could extend well past late February into March and into late spring, based on current intensity, number of early cases, and ongoing hospitalizations and deaths recorded at this point,” Glatter said. “We typically see about 20,000 to 50,000 deaths during a typical flu season, but we could see double or even triple that number this flu season.”

Is There a Chance This Year’s Flu Season Won’t Get Any Worse?

Other experts caution that while it’s the earliest we have seen this level of flu activity since 2010, it is too soon to know how severe the flu season will be, especially considering the course of flu seasons can fluctuate.

“We have a lot of illnesses and hospitalizations right now for this time of year, but it’s unclear how things will look at the end of the season,” Jhung said. "If activity continues the way it is now, it’s possible this will be a severe season, but if activity drops off suddenly, it’s possible that the total burden of flu this season will be relatively mild."

How Can I Avoid Getting Sick?

As seasonal flu activity continues to rise across the country, experts say that it’s never too late to take preventive steps to protect yourself and your loved ones. Here’s what the CDC recommends you do to reduce your chances of getting the flu this year:

• Get your flu vaccine
• Avoid touching your eyes, mouth, nose, and face
• Wash your hands frequently and properly
• Wear a mask
• Cover your mouth when coughing or sneezing
• Avoid being around people who are sick

Flu shots are especially important for adults age 65 and older, children younger than age 5, pregnant people, and people who are immunocompromised. Even if they get sick, having had a flu vaccine can help prevent complications.

"[A flu shot] not only protects you, it protects people around you who may be more vulnerable to the flu or who may be unable to get the vaccine," Kappagoda said.