- This year’s flu vaccine isn’t a perfect match against the dominant influenza strain circulating at the moment.
- Although this season’s shot contains a version of H3N2, the H3N2 strain circulating has picked up new mutations, leading to a slight vaccine mismatch.
- Experts, however, say that even an imperfect flu shot can provide strong protection against illness and, more importantly, hospitalization and death.
This year’s flu vaccine isn’t a great match against the dominant influenza strain circulating right now, according to a recent preprint study.
While this might sound alarming, experts say it’s actually unusual for there to be a perfect match between the flu shot and the circulating strains.
One of the strains included in this year’s shot — H3N2 — has picked up multiple mutations, leading to a vaccine mismatch.
The slight mismatch identified in the study doesn’t mean that the shot is no longer effective, according to experts.
In fact, the flu shot will still be able to prevent many illnesses and keep many more who get sick with the flu out of the hospital, says Dr. William Schaffner, an infectious diseases specialist at Vanderbilt University in Nashville, Tennessee, and the medical director of the National Foundation for Infectious Diseases.
“Even if you get flu with that strain, you’re very likely to have a less severe infection,” Schaffner told Healthline.
According to Dr. Marie-Louise Landry, the director of the Clinical Virology Laboratory and professor of laboratory medicine and medicine (infectious diseases) at Yale School of Medicine in New Haven, Connecticut, the influenza vaccine contains four different influenza strains: two A and two B.
The circulating H3N2 strain has multiplied millions of times and in that process mutated to be slightly off target from the vaccine.
Even though the version of H3N2 that’s included in this year’s shot is an imperfect match to the H3N2 strain going around, there’s still substantial overlap between the strains for the shot to provide meaningful protection, according to Schaffner.
The drift may mean that shot may be slightly less effective at preventing infections, but it should still help lessen the severity of disease, Landry told Healthline.
In addition, the shot may still do a good job of targeting other A and B strains that are circulating.
“Even if there is a mismatch for one, the vaccine can prevent infection with the other three, and there may be milder disease with the breakthrough virus,” Landry said.
We should have a better idea of how effective this year’s shot is toward the middle of the flu season.
Most H3N2 infections have occurred in children and young adults between the ages of 5 and 24.
“If that holds true, older persons might be at somewhat greater risk because we know those H3N2 viruses preferentially do their mischief in older persons,” Schaffner said.
H3N2 strains are known to cause more severe illness in older adults, while B strains are known to have a greater impact on children.
Landry says that H3N2 seasons are typically associated with more deaths, but it’s also common to see different strains take off over the course of the season.
“So far, the circulating flu seems to be mostly H3N2, but other influenza strains often appear over the course of the season, sometimes in successive waves,” Landry said.
The preprint report warned that the population may have lower immunity due to last year’s inactive flu season.
Some epidemiologists suspect that because there weren’t circulating influenza strains naturally boosting immunity, this year’s flu season may be more severe.
But Schaffner says that it’s too soon to know if and how last year’s absent flu season will impact flu activity this year.
So far, the 2021–2022 flu season is looking like it will be a moderate one.
“Not a tiny one, not a really bad one — but, nonetheless, a moderate flu season,” Schaffner said.
Nonetheless, even a moderate flu season will cause many hospitalizations and deaths.
Schaffner says that the focus continues to be on COVID-19, but he wants to remind people that the flu is back and it’s not too late to get the influenza vaccine.
It’s safe to get your COVID-19 vaccine and influenza vaccine at the same time. Additionally, the precautions used to prevent COVID-19 can help reduce influenza infections, too.
“The recommendations are simple: If you’re over 6 months of age, you should get your annual flu vaccine,” Schaffner said.