RIT scientist says people can think of the annual flu shot as an important update for the immune system

Rochester, New York – Getting an annual flu vaccine can be thought of as installing a new software update for the immune system, according to Andre Hudson, dean of the Rochester Institute of Technology’s College of Science.

Hudson, an expert in biochemistry and microbiology, said influenza viruses are constantly changing. Because of those changes, scientists regularly monitor the viruses and update the seasonal vaccine to make it more closely match the strains they expect to spread.

The basic idea is fairly simple. A vaccination gives the immune system an advance look at what it may encounter during the upcoming flu season. When the vaccine is updated, the immune system receives a newer picture of the virus.

“Influenza is a moving target,” said Hudson. “Flu viruses are constantly evolving. As influenza viruses replicate, genetic changes accumulate.”

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Those genetic changes can affect proteins found on the surface of influenza viruses. These proteins are among the features recognized by antibodies produced by the immune system.

Hudson explained that this gradual change is known as antigenic drift. As influenza viruses continue to change, strains circulating in a particular season can become different from earlier versions. When that happens, antibodies developed after exposure to previous strains may not recognize the newer viruses as effectively.

That is one reason scientists do not simply rely on the same flu vaccine year after year.

Researchers around the world keep track of influenza activity, watching which strains are circulating and how the viruses are changing. The information gathered through this surveillance is then used to help determine which influenza strains should be included in vaccines for a particular season.

There is an important complication, however. Scientists have to make decisions about future virus activity before the flu season arrives.

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According to Hudson, researchers use predictive modeling to estimate which strains are likely to circulate and how they might change. Those predictions involve some uncertainty because viruses can continue to mutate after scientists have made their selections.

The vaccine also has to be prepared ahead of time. Since vaccination is intended to prevent illness, doses need to be available before or during the beginning of the flu season rather than being developed after the viruses have already spread widely.

The Centers for Disease Control and Prevention reports that all three virus components in the 2026-2027 U.S. seasonal flu vaccine were updated compared with the previous season.

The CDC identifies December through February as the peak flu season in the United States. Monitoring influenza throughout the year therefore remains an important part of preparing for the months when flu activity is expected to be highest.

For Hudson, the software-update comparison offers a straightforward way to understand why the flu vaccine changes over time. The virus changes, scientists track those changes, and the vaccine is adjusted to provide the immune system with a more current preview of the influenza strains it may encounter.