A woman wears a button after getting a flu shot at a Walgreens drug store in Portland. Credit: Troy R. Bennett / BDN

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Sheldon Jacobson is a professor of computer science at the University of Illinois at Urbana-Champaign. Janet Jokela, an infectious disease and public health physician, is senior associate dean in the Carle Illinois College of Medicine at the University of Illinois.

Flu season is fast approaching. Flu shots are now available, containing strains recommended by the Food and Drug Administration’s vaccine advisory committee in March. Given the long lead time required to manufacture some 180 million flu shot doses, scientists are forced to make informed guesses, a daunting task under the best of circumstances.

The Southern Hemisphere has already seen its worst flu season in five years. This is not surprising, given that the COVID-19 virus and variants likely overwhelmed other circulating viruses over the past three years, with the flu considered to be less infectious than COVID-19.

Do the experiences in the Southern Hemisphere guarantee that we will also experience a severe flu season in the U.S.?

Some believe so, but it does not necessarily have to be that way.

Studies have shown that city size affects the length and severity of a flu season. Large densely populated urban areas such as New York, Chicago and Boston are prone to an early and long flu season, though not necessarily with surges or spikes in cases.

There are many other factors that could either attenuate or amplify the severity of the flu season here.

Flu vaccine uptake: After two shots and two boosters for COVID-19, people are dealing with vaccine fatigue. With a COVID-19 bivalent booster now available for most populations, will people be willing to get a bivalent booster and flu shot this fall?

Getting people to receive boosters against COVID-19 has been a challenge. Only a little more than half of the eligible adult population have gotten one booster, and only about 35 percent of those older than 50 have gotten two boosters, according to the Centers for Disease Control and Prevention. Even among those 65 and older, the group most vulnerable to severe cases of COVID-19, just 43 percent have gotten two boosters. This group is also most vulnerable to severe outcomes from influenza. Expecting more willingness to be vaccinated against anything, let alone the flu, may be a stretch.

Strain match: The match of the flu vaccine to the circulating virus strains will determine how much protection the flu vaccines provide. If the match is good, the vaccines will provide significant protection. Historically, flu vaccines have reduced the risk of contracting the flu by 40 percent to 60 percent when the strains are well matched. This qualifier is a big “if” since the match will be unknown until epidemiological data is collected as people become infected.

Over the past eight flu seasons, the most protective season for the flu vaccines has been 2015-16, with 48 percent risk reduction effectiveness, while 2014-15 was the least protective season, with 19 percent effectiveness.

Face masks: Face masks reduce the risk of virus transmission, provided they are high quality, such as N95 and KN94, well fitted and worn correctly. If any of these conditions are relaxed, then the benefits of face masks drop precipitously. Those who have benefited from wearing face masks in crowded indoor venues with poor air ventilation will continue to accrue such benefits during flu season. Those who decline to wear face masks will be at a higher risk of infection. Other countermeasures such as hand-washing will also suppress the spread of the flu. Sometimes, the simplest techniques can have a profound impact.

Given that the 2020-21 flu season was effectively nonexistent and the 2021-22 season mild, it remains to be seen how the 2022-23 season will pan out. The good news is that after 30 months with COVID-19, a sector of the population, including the most vulnerable, such as those older than 65, has adapted to mitigating transmission of infectious diseases. If such countermeasures continue, this can have a positive impact on reducing the severity of this flu season and certainly provide such people with personal protection.

In simple terms, every infection not spread is a win for everyone. How people act and behave will determine the number of such wins.