A South Arkansas Community College practical nursing student gives a flu shot during the Arkansas Department of Health flu clinic in El Dorado, Ark., Oct. 25, 2013.(Photo: Michael Orrell, AP)
Flu vaccines were only 19% effective in preventing doctor visits for influenza this season, one of the lowest rates in the past decade, the Centers for Disease Control and Prevention said Thursday.
Health officials had predicted flu shots would be less protective than usual this year. That's because the viruses used to make the flu shots weren't a good match for the dominant strains of influenza in circulation, said Brendan Flannery, an epidemiologist in the CDC's influenza division.
Scientists face a difficult challenge each year when selecting the virus strains to be included in seasonal flu shots, said Andrew Pekosz, an associate professor at the Johns Hopkins Bloomberg School of Public Health in Baltimore. That's because flu viruses, unlike the measles or polio viruses, undergo significant genetic changes each year. So the vaccine needs to change every year, too.
Scientists from the CDC and Food and Drug Administration survey the dominant flu strains annually and make their selections in February, Flannery said. That gives manufacturers about six months to produce the vaccines, which ship out to clinics the following fall. Last year, however, flu viruses began mutating almost as soon as companies began production.
"This is a perfect example of what happens when the virus and the vaccine don't synchronize," Pekosz said.
In the past decade, effectiveness rates for flu shots have ranged from 10% to 60%, according to the CDC.
A so-called universal flu shot could solve this problem, said influenza expert Arnold Monto, a professor of epidemiology at the University of Michigan School of Public Health. These shots would be made with parts of a flu virus that don't change every year. Ideally, one shot would protect people for at least several years.
Given the complexity of developing universal flu vaccines, they're unlikely to be available to the public for another five to 10 years, Monto said.
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Flu kills 3,000 to 49,000 Americans each year, according to the CDC. More than 140 children died from the flu this season in 40 states and New York City, according to the new CDC report. Only about half of Americans get a flu shot each year, although the CDC recommends them for everyone over age 6 months.
In spite of the flu shot's limitations, people are still better off being vaccinated, Pekosz said.
"There's nothing harmful about the vaccine," Pekosz said. "There's no disadvantage to getting it."
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