Colorized 3D renditions of influenza virus based on a model created by NIH 3D, originally derived using electron microscopy. Image: NIAID
At a glance:
- First large-scale analysis of optimal timing for flu shots finds October is the best month for children to get vaccinated against influenza.
- Study of 800,000 pediatrician visits leverages links between children’s birth month, annual physical schedule, and vaccination timing.
Children born in October are most likely to be vaccinated for the flu in October — and are least likely to be diagnosed with influenza, according to results of the first large-scale study of optimal timing for the flu shot. Findings are published Feb. 21 in the BMJ.
The study, by researchers from the Department of Health Care Policy in the Blavatnik Institute at Harvard Medical School, amplifies public health guidance that encourages getting flu vaccinations in October for those in the northern hemisphere.
“There are a lot of variables when it comes to the timing and severity of flu season or a person’s risk of getting sick, and many of those are out of our control,” said Anupam Jena, the Joseph P. Newhouse Professor of Health Care Policy at HMS, physician at Massachusetts General Hospital, and senior author of the study. Christopher Worsham, HMS assistant professor of medicine and critical care physician at Mass General, led the study.
“One thing we have some control over is the timing of the shot,” Jena said, “and it looks like October is indeed the best month for kids to get vaccinated against the flu.”
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In January the U.S. Centers for Disease Control and Prevention reported at least 150,000 hospitalizations and 9,400 deaths due to flu as of the time of the report and noted that high demand for hospital care for influenza has contributed to strained hospital capacity in some parts of the country. Over the past decade in the U.S., between one and 199 children have died of influenza each flu season. Across the years, most children who die are not fully vaccinated against the flu.
Part of the reason the timing of the shot is tricky is the way the immune system responds to a vaccine. If a person gets the shot too early, their immunity may fade by the time flu season peaks. If they wait too long, their body may not have time to build immunity strong enough to protect against the peak level of infections.
How soon is too soon, and how late is too late?
Public health recommendations in the U.S. have long promoted September and October flu shots, but Jena said there has never been a randomized clinical trial to test the best timing, nor a large-scale effort to see how likely people who get vaccinated in other months are to get sick.
When Jena was at a late summer meeting in 2022, he mentioned that his arm was sore from getting his flu shot. A colleague asked whether he was concerned about his immunity waning before flu season.
“It hadn’t occurred to me to check if one month or the other might make a big difference,” Jena said. “When we looked at the science, we were surprised that no one had ever looked at the question in a big population.”
Organizing a clinical trial would require a lot of time and resources to coordinate the random distribution of flu jabs across hundreds or thousands of people.
But Jena, Worsham, and study co-author Charles Bray, HMS research assistant in health care policy, had a good idea where they could find an already randomized study population.
Science Matters with Anupam Jena | Health Care Economics and Physician Behavior. Video: Rick Groleau
The Written Word: Random Acts of Medicine with Anupam (Bapu) Jena and Christopher Worsham. Learn more
