Flu vaccine same as last year’s: will you need to get it again?

By Deborah Kotz, Globe Staff

I dutifully got my flu vaccine last year -- for the first time -- after being scared straight by the previous summer’s H1N1 pandemic. But now I’m not sure whether I need to get vaccinated again this fall since the US Food and Drug Administration announced yesterday that the immunization will contain the identical strains of the virus as last year’s.

The FDA says yes. “It is important to get vaccinated every year, even if the strains in the vaccine do not change,” said Dr. Karen Midthun, director of FDA’s Center for Biologics Evaluation and Research, “because the protection received the previous year will diminish over time and may be too low to provide protection into the next year.”

Still, I find it hard to believe that the vaccine really does wear off after a year given that other immunizations against, say, measles and polio can last for years or even decades.

But the US Centers for Disease Control and Prevention says on its website that, yes, it’s best to have an annual vaccine even if it’s the same formulation you received last year in order to get “optimal protection,” specifying that a decline in protection from the previous year’s immunization “has the potential to leave some people more vulnerable to infection, illness and possibly serious complications from the same influenza viruses a year after being vaccinated.”

This group of vulnerable individuals includes elderly folks and those with chronic health conditions that weaken their immune system.

On the other hand, researchers in a 2008 study published in Nature found that we have the ability to retain antibodies to specific flu strains for an entire lifetime, at least for those who were naturally infected with the virus back in 1918.

But your body’s immune response to the flu vaccine is weaker than when you’re actually infected with the virus, and it’s not known whether that weaker response lasts long enough to fight off the same flu strains circulating a year later. “It’s actually a very good question, and I’m not sure it’s been studied since different strains usually circulate every year,” said Eric Altschuler, assistant professor of physical medicine and rehabilitation at the University of Medicine and Dentistry of New Jersey, and co-author of the Nature study.

While experts speculate that some people probably do retain this protection, it’s impossible to predict with certainty who will and who won’t. For this reason, we’re all told to get revaccinated. But if you’re worried about the risks of getting the same vaccine twice in two years, Altschuler adds, talk to your doctor.