WEDNESDAY, June 3, 2026 (HealthDay News) -- For children aged 2 to 5 years, those with fall birthdays are more likely to be vaccinated and less likely to be diagnosed with influenza, according to a research letter published online June 1 in JAMA Pediatrics.
Christopher M. Worsham, M.D., M.P.H., from Massachusetts General Hospital in Boston, and colleagues examined the efficacy of influenza vaccination across recent individual influenza seasons from 2016 to 2023 among children aged 2 to 5 years with fall versus summer birthdays.
The researchers found that children with fall birthdays were more likely to be vaccinated and were less likely to be diagnosed with influenza in each of the influenza seasons examined. Depending on the season, influenza vaccination rates were 8.6 to 12.5 percentage points higher in absolute terms among children with fall versus summer birthdays, and influenza diagnosis rates were 1.0 to 1.4 percentage points lower. No differences were seen in diagnosis rates of noninfluenza viral infection falsification conditions. For every 100 children who were vaccinated because of the timing of their birthday, there were nine to 14 fewer diagnosed cases of influenza, depending on the season.
"It is impossible to do a randomized controlled trial for every single thing that we want to know and understand," senior author Anupam B. Jena, M.D., Ph.D., from Harvard Medical School in Boston, said in a statement. "But we have an incredible amount of data out there and there are randomized experiments like this sitting in that data, waiting to be uncovered."
One author disclosed ties to the health care industry; two authors disclosed ties to the publishing and media industries.
