Most years, senior citizens are among the groups hit hardest by flu, which is why doctors recommend all people over 65 get vaccinated. But accurately measuring how well the vaccine does at preventing severe disease and deaths isn’t as straightforward as it is in younger populations.
A lot of factors complicate getting accurate information on the number of flu cases among older adults and the vaccine’s role at preventing them, and some have argued that current estimates of the flu vaccine’s effectiveness are overblown because they don’t account for such factors. For example, sometimes patients are left unvaccinated because they are already medically frail and struggling with a lot of other health issues. So simply counting the number of deaths among unvaccinated patients versus vaccinated patients might not paint an accurate picture.
Last month, a study led by Vincent Mor, PhD, of Brown University, looked a little closer at the vaccine to assess its effectiveness. The research team analyzed 10 years of Medicare claims for nursing home residents, taking advantage of a built-in variation.
Because the flu virus changes over time, the vaccine has to be updated every year to fight against the strains that are circulating that year. Some years, the vaccine matches what’s circulating better than other years. (Last year, in the 2014-2015 season, the vaccine strain didn’t match the flu viruses infecting people very well.)
If the vaccine isn’t effective in elderly patients, then we shouldn’t see any difference in flu cases from year to year. But Mor and his colleagues found that the better the vaccine strain matched the circulating viruses, the better the vaccine was at protecting elderly nursing home residents. They argue that this indicates that the vaccine protects people living in nursing homes from serious outcomes associated with influenza infection.
This isn’t an approach we can take with other types of vaccines. It’s only possible because the flu vaccine changes from year to year. "What we've used is the randomness of the match," Mor said in a statement. "Ours is the first study to, we think, come up with an unbiased approach."
Though this study probably won’t settle the controversy about how well the vaccine works in older people, it does offer a different way to look at the question. A variety of other novel approaches are probably what it will take to get a handle on this hard-to-understand aspect of influenza.
Previously: Science Friday-style podcast explains work toward a universal flu vaccine, Study: Pregnancy causes surprising changes in how the immune system responds to the flu and Gut bacteria may influence effectiveness of flu vaccine
Photo by Cynthia Goldsmith