Why Did Flu Season Start So Early This Year?

Why Did Flu Season Start So Early This Year?

The U.S. influenza season arrived earlier than usual. The Centers for Disease Control and Prevention detected the early flu activity in mid October. The phenomenon was being observed in most areas of the country, with a greater intensity in the Southeast and south-central regions. The virus’s levels continue to rise rapidly a month later. According to the latest CDC flu report, 25 states or jurisdictions now experience high or very high levels of outpatient visits for influenza-like illness, which is characterized by fever plus cough or sore throat.

William Schaffner, a Vanderbilt University School of Medicine professor, said that the rise in infectious diseases occurred four to six weeks earlier than normal. Every flu season is unique, but the sudden arrival of the season was not expected. He says, “It was a very surprising, even to the expert influenza watchers that influenza appeared and rose dramatically and became very common so early in the season.”

Tennessee is home to Schaffner. It is one of the most affected jurisdictions for respiratory illness. Schaffner states that one third of patients who come into our urgent care clinic at the medical center are positive for influenza. “That’s huge, and it indicates a very broad spread,” Schaffner says. Schaffner also noticed an unprecedented rise in influenza-infected patients over the past three week.

The CDC estimates that so far this season, there have been at least 2.8 million illnesses, 23,000 hospitalizations and 1,300 deaths from flu.

Chart shows number of positive flu tests in the U.S. reported to the WHO each week from January 2017 through October 2022.
Credit: Amanda Montanez; Source: FluNet/Global Influenza Surveillance and Response System at the World Health Organization (data)

Why Did the Flu Arrive So Early?

Experts say it is not clear what caused the early flu season. It is impossible to predict how severe the flu season will be.

Flu all but disappeared in the U.S. in 2020 to 2021, which coincided with the COVID pandemic. According to the CDC, this lackof exposure to flu may have affected immunity. According to the CDC, a reduced population immunity, especially among young children who may not have been exposed to flu or vaccinated, could lead to a strong return of flu.

” Typically, the population level immunity is what matters in terms of how many infection we are going to see in a given season,” says Arnold S. Monto (a professor of epidemiology at The University of Michigan School of Public Health). He says that “now almost everyone is going around unmasked, so [flu] transmission could go back to what they have normally seen,” he said. He adds that the fact that less people have antibodies to the flu now, because they were not exposed to it during the pandemic, may be helping to spread the virus.

This doesn’t mean that a person’s immunity system is impaired by lack of exposure to a particular virus. It’s a misconception sometimes called “immunity debt” or “immunity loss.” Schaffner states that this doesn’t mean that our immune system has been compromised. “We are still fully capable of fighting the virus and responding .”to the vaccine,” Schaffner says.

What Happened in the Past Two Years?

The low number of flu cases over the past two years can often be attributed to the implementation preventive measures against COVID such as social distancing and masking.

While these behaviors may have played a significant role, there could be other factors. According to epidemiologist Michael Osterholm, director of the Center for Infectious Disease Research and Policy (CIDRAP) at the University of Minnesota, the key to understanding why other respiratory viruses all but disappeared in 2020 and 2021 lies in how these viruses interact with each other.

” We have learned that seasonal viruses can slow down the growth of other viral respiratory pathogens. One example of this phenomenon, known as viral interference, goes back to the 2009 H1N1 influenza pandemic, when almost no one was practicing social distancing or masking. Researchers believe that the circulation of a type of common cold virus called human rhinovirus (HRV) in France may have delayed the H1N1 influenza epidemic in that country. Subsequently, H1N1 seems to have delayed the following local wave of the common virus known as respiratory syncytial virus (RSV). (RSV is now surging again in the U.S., after a pause during the COVID pandemic’s first year and a large peak in cases in summer 2021. )

While RSV is still increasing nationally, it recently started to decrease in the Southeast and in south-central and north-central parts of the country, according to a recent CDC media briefing. “It seems like RSV has started to trend downward in those three regions,” Jose R. Romero (director of CDC’s National Center for Immunization and Respiratory Diseases) said during the briefing. Scientists are increasingly interested in this type of interference, although it is still not clear how these viruses interact on a population-level.

What Can People Do to Protect Themselves?

While it is impossible to predict how big the 2022-2023 flu season will be, Schaffner says it’s safe to assume that there will be plenty of flu transmission during November and into December, since the western and northwestern parts of the U.S. have not yet been affected extensively.

Vaccination is the best way to protect yourself from the flu, experts say. The CDC recommends that everyone six months old and older receive the flu vaccine annually. That includes pregnant people. If you haven’t had your shot yet, it is a good time to do so. Experts warn that the vaccine does not guarantee you will not get infected. But much like the COVID vaccine, it considerably reduces the risk of serious illness and hospitalization. You can get information on flu and COVID vaccination sites at Vaccines.gov. It’s safe to receive both shots at the same time.

The CDC estimates that, as of mid-October, more than 26 percent of adults had received a flu vaccine this fall–slightly higher than the estimated 23 percent at the same time last season. This level of coverage is similar to the most recent flu season before the pandemic, when flu shot coverage was 29 percent in adults by the end of October 2019, according to the CDC.

Additional habits to prevent the flu are avoiding close contact with people who are sick, staying home when you have symptoms, covering your mouth and nose with a tissue when coughing or sneezing, and washing your hands often. You might also consider masking once more. Monto states that masking is a good idea if you are in an area where people are close to one another. “Masking will stop transmission of COVID and the flu .”

,” Monto says.

Vaccination is still the best way to prevent severe diseases, regardless of how severe the flu season turns. Schaffner states that predictions about flu are dangerous because they are often wrong. “This is not something that we should attempt to predict to decide whether or not to get vaccinated. Just get vaccinated every year.”


    Mariana Lenharo is a science and health journalist with a Masters in journalism from Columbia University. Follow Mariana Lenharo on Twitter

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