Another flu season, another less than effective flu vaccine. The shape-shifting virus has mutated already and this year’s flu vaccine is a poor match to fight it.
Another flu season, another less than effective flu vaccine. The shape-shifting virus has mutated already and this year’s flu vaccine is a poor match to fight it.
Professor of microbiology at the University of Pennsylvania Scott Hensley found that the current flu vaccine is a “major mismatch” for this season’s H3N2 strain. The vaccines are quadrivalent, meaning they protect against four different flu virus strains. Hensley’s study only looked into H3N2, but that’s the primary strain circulating right now. This doesn’t bode well for the vaccines efficacy at preventing infection.
The H3N2 strains tends to mutate faster than other strains. In the past, when this strain has been dominant, more hospitalizations and deaths have occurred.
The poorly matched vaccine, coupled with the fact that the general population’s influenza immunity is down from record-low numbers in 2020, is most likely gearing the U.S. up for a particularly nasty flu season.
An October outbreak at the University of Michigan had the CDC sending in a team last month to investigate the close to 800 cases reported on campus. More than 26% of the students and staff who tested positive for the flu had been vaccinated. This was the same percentage as those who tested negative, supporting the theory that the vaccine is not preventing infection.
Flu viruses mutate far more frequently than other viruses, including the coronavirus. That’s why the shot is updated every year based on the best guesses for the coming season, based off of what scientists saw in the opposite hemisphere’s flu season. Choosing the strains to cover six months ahead of flu season gives manufacturing processes the time they need, but also gives the virus more time to mutate again.
In light of the major mismatch, experts still recommend the flu vaccine. While it may not prevent infection this year, it still helps protect against severe illness and death.
“Studies have clearly shown that seasonal influenza vaccines consistently prevent hospitalizations and deaths even in years where there are large antigenic mismatches,” Hensley said in the study, which has not yet been peer-reviewed or officially published.
This certainly isn’t the first year the flu vaccine has shown less than stellar effectiveness. The best year in the past nearly two decades was 2010-2011 flu season, where the CDC reported the shot as 60% effective. The worst was in 2004-2005 when the vaccine clocked in at a paltry 10% effective. Even last year the shot was “not a very good match,” yet with COVID-19 precautions in place, numbers were so low the CDC didn’t even bother to estimate efficacy for that year.
The poor performance of the 2014-2015 flu vaccine was also attributed to a mismatch to the circulating H3N2 strain that year. According to the CDC, that flu season resulted in an estimated 30 million cases of influenza infection, 591,000 hospitalizations and 51,000 flu-associated deaths for the U.S. They clocked in the overall flu vaccine effectiveness at less than 20%, while effectiveness against H3N2 was only 6% for the season.
Historically, a ferret model has been used to predict antigenic changes for influenza vaccine strain selection. The manufacturing process is started months before flu shot administration begins. The most common flu vaccines are produced from viruses grown in chicken eggs, which take weeks to incubate.
The big names that brought us the first mRNA vaccines to fight the COVID-19 epidemic have turned some of their attention to the seasonal influenza vaccine. Moderna just posted positive interim results last week from their experimental flu vaccine. Pfizer began its study for a single dose quadrivalent flu vaccine in healthy adults in September. The beauty of the mRNA vaccine is that it could potentially be updated relatively quickly to match the most prevalent strain that rears its head as the flu season begins. Current vaccines can’t offer that kind of flexibility.
This year health officials are preparing for a double whammy of flu and a rapidly rising number of Omicron COVID-19 infections. Even with less-than-impressive efficacy numbers, vaccination remains our best defense against serious disease and death.
