Can a flu shot wear off if you get it too early? Perhaps, scientists say

By HELEN BRANSWELL @HelenBranswell

t can be jarring to see placards advertising “Flu Shots Today” in late July or early August in 80-degree weather.

But those signs may be more than just an unwelcome reminder that summer’s days are numbered. Mounting scientific evidence is raising questions about whether vaccinating people that early may actually be undermining the effectiveness of the nation’s massive flu vaccination program.

Studies from the US and Europe have detected a steady decline in vaccine protection in the months after vaccination. The most recent research, published just last month by scientists from the Centers for Disease Control and Prevention, showed that the vaccine’s effectiveness was reduced by more than half for a couple of strains of flu, and had diminished almost entirely for another by five or six months after vaccination.

More research is needed to confirm the findings. But Michael Osterholm, director of the Center for Infectious Diseases Research and Policy at the University of Minnesota, said there’s enough evidence now to suggest early vaccination efforts — part of an attempt by commercial pharmacies to capture a bigger piece of the flu vaccine pie — should be discouraged.

“I have been concerned for some time that we have gotten into the marketing of influenza vaccine versus the effective use of influenza vaccine. And we’ve got to reconsider that,” Osterholm told STAT.

“Until we get more data, frankly I think the very best approach is to try to make sure we get flu vaccine into people just before flu activity starts, not something convenient to when the marketers want to get people in the door of department stores and grocery stores.”

Other scientists say it’s too soon to jump to a conclusion that would require changing recommendations. The CDC currently advises people should be vaccinated by the end of October.

“Is there waning [of protection] within a given season? I do think the evidence is growing and it’s growing in a way that suggests that there is something there. But we need more information,” said Jill Ferdinands, an influenza epidemiologist at the CDC and the lead author of the most recent article on this question.

Influenza vaccination programs are a major public health endeavor. Although the annual effort always falls short of vaccinating everyone — the CDC estimated that only 40 percent of people had been vaccinated by early November, its most up-to-date data — the US uses more than 100 million doses of flu vaccine every year. So far this year, manufacturers have shipped nearly 148 million doses.

Once people are vaccinated, it takes about 14 days for the immune system to generate a protective response, a factor in the debate over timing.

“It is hugely disruptive to try to immunize millions of people in a six- to eight-week period beginning in October or November. So I understand in the context of a universal immunization program, to get the vaccine into all those arms it’s nice to be able to start earlier,” said Dr. Danuta Skowronski, a flu epidemiologist at the British Columbia Center for Disease Control.



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