The Variable in the Vaccine

Why This Year’s Flu Season is the Worst in a Decade

By Breanna Beers

Flu season is now in full swing, and for an illness with a vaccine readily available since the 1940’s, the virus seems to be running rampant across the United States. According to the Centers for Disease Control (CDC), this year’s flu season is may be worse than any in nearly a decade, and is nowhere close to being over yet.

There are several different categories of influenza strains, broken down by the proteins on the surface of the virus. These proteins are what the immune system uses to recognize and fight the illness. The CDC reported that over 80% of flu cases in the United States this year have been H3 strains, which tend to be both more deadly and more adaptable than their H1 cousins. And adaptability, according to biology professor Dr. Heather Kuruvilla, is the key factor in the success of a virus.

“The flu, like any virus, has a pretty high mutation rate, and so it’s always evolving resistance to immune systems,” Kuruvilla explained. “Otherwise they would all die off, because you’d basically develop antibodies against it the first time you saw it, and that little parasite could never get to you again.”

Critically, the virus is not evolving resistance to the vaccines; it’s changing in response to the immunity of its host population — in this case, humans. Strains that have already moved through the population  are quick to die out, leading to slightly mutated forms taking over in a rapid cycle.

“If the virus didn’t keep evolving, people would only get the flu once, then you would never need flu shots again,” said Kuruvilla. “[If] the protein structure is slightly different than the other flu strains’ protein structure…the antibodies you’ve made against the flu may not stick to it that strongly, and it can basically evade your immune defenses.”

That’s why, although flu vaccines have been around for nearly 80 years, the virus continues to sweep through the United States every year from November to March. Since there are predictable times of the year when the flu will be more common, researchers have time to produce the vaccine in preparation. However, since it can take up to six months to grow, prepare, and distribute the vaccine, manufacturers have to make an educated guess about which strains will be most common in a given year, based on constant monitoring of the virus.

This can create problems, though, since influenza has a particularly high mutation rate — H3 even more so than many other strains. Even if researchers can accurately predict which subtype of virus — H1, H3, B, et cetera — will make the rounds in a given season, small changes within that category can be enough to get around the body’s immune defenses, rendering the vaccine ineffective.

Both of these problems were manifested in this year’s flu shot. The vaccine underestimated the scope of H3, which turned out to be the most common strain this year. While it did contain one version of the H3 virus, the lab-grown virus was cultured in chicken eggs. According to Kuruvilla, this allows scientists to produce the vaccine at higher quantities at a reduced cost, which makes it available to a wider segment of the population.

“It’s really easy to grow up viruses in something like eggs,” Kuruvilla explained. “It’s much more expensive and more difficult to scale it up to that production level in human cells. It can be done, but it is going to be more expensive to get it out. They’re trying to keep the scale high and keep the costs low, so that more people can have access to the flu vaccine.”

However, this can occasionally come with downsides. While in culture, the virus adapted to the environment by adding an extra sugar to the outside of the cell, which allowed it to survive better in the eggs. This meant that the version of the virus that ended up in the vaccine was also modified, and didn’t match the strain that was actually making the rounds in humans, resulting in drastically diminished effectiveness.

“You might know somebody who got the flu even though they got the flu shot, and it’s just because they happened to catch a strain that was not one of the strains that was protected against,” said Kuruvilla.

Despite the reduced potency of the flu shot, the CDC is still recommending vaccination across the board. More vaccinations can help contribute to herd immunity — if a person can’t catch the virus, they can’t help spread it to others. And vaccination can still fight other strains of the flu that are also going around, including some H1 varieties, which tend to appear more prevalently later in the season.

Breanna Beers is a freshman Molecular Biology and Journalism double major and an off-campus news writer for Cedars. She loves exercising curiosity, hiking new trails, and quoting The Princess Bride whether it’s relevant or not.