Some people who seemingly never get the flu got sick last season – even some who got a flu shot. Scientists in Seattle think they know why and whether it will happen again.
The age groups hit hardest by the seasonal flu are typically the young and the elderly, but something odd happened last season. A lot of people in their 30s and 40s got sick.
“Overall, in the last flu season, there was a higher than normal rate of severe influenza infection which includes people being hospitalized and going to the doctor, the types of things that get reported, among this middle-aged group,” said Jesse Bloom of the Fred Hutchinson Cancer Research Center in Seattle.
More specifically, it hit people born between 1965 and 1979. Bloom contributed to research at the Wistar Vaccine Center in Philadelphia that might explain why. Flu strains circulating in the 1970s and early 80s caused people who were first infected with those strains to have their immune response target a certain part of the viruses.
“In modern viruses, that part of the virus has changed and what that means is that the immune response that the vaccine elicits in middle-aged people is actually less effective than in younger and older people,” Bloom explained.
Bloom said over the years, we are exposed and vaccinated many times and our immune system has a memory and usually targets the virus correctly, unless it mutates. There was a mutation in the H1N1 virus last year.
“We think in this particular case, that may have actually been what happened in this middle-aged group. One of the goals is, can we design the vaccine in future years so the vaccine is sort of able to help remedy this problem,” said Bloom.
It’s not a simple matter of adding more virus strains to the annual vaccine. Bloom said there are far too many flu strains to protect against all of them.
“The choice of which viral strain to put in that vaccine is always a challenging decision and our work provides a little insight into how. In certain cases, we might be able to make little bit better decisions about that,” offered Bloom.
Just because the flu vaccine was less effective for one group of people doesn’t mean you should skip it altogether, cautioned Bloom. As for people in their middle years, Bloom said most scientists believe the dominant flu strain this year will be something other than H1N1 so there’s no reason to expect a repeat of the strange phenomenon of the 2013-2014 flu season.