Study shows autumn-born children more protected by annual flu shots, highlighting vaccination timing need

Research in JAMA Pediatrics reveals that children born earlier in the year are more likely to be vaccinated and less susceptible to influenza, prompting renewed discussion on the importance of timely annual flu shots for young children.

A new research letter in JAMA Pediatrics adds to evidence that annual flu shots help protect young children, finding that those born earlier in the year were more likely to be vaccinated and had lower rates of influenza than children with summer birthdays. The study, led by Christopher M. Worsham, comes as paediatric flu vaccination has drawn fresh scrutiny in the United States after the Centers for Disease Control and Prevention removed annual influenza vaccination from its childhood immunisation recommendations earlier this year.

To get around the usual weaknesses of observational research, the authors used birth month as a natural experiment. Because flu vaccines are generally available from mid-August and young children often receive routine check-ups around their birthdays, children born in the autumn were more likely to get vaccinated than those born in the summer. The analysis covered five flu seasons between 2016 and 2023, leaving out the two COVID-affected seasons in 2020-21 and 2021-22.

The difference in uptake was clear in the 2022-23 season, when 50.8% of children aged 2 to 5 born between September and November were vaccinated, compared with 38.3% of those born between June and August. Influenza infections were also less common among autumn-born children, at 7% versus 8.4% in the summer-born group. After adjusting for vaccination coverage, the researchers estimated that the shot prevented 10.9 cases per 100 vaccinated children that season, with protection across the study period ranging from about 9 to 14 cases averted per 100 vaccinated children.

The findings align with a broader body of recent research showing that flu vaccination can reduce both infection and severe outcomes in children. A July study in JAMA reported an 80% effectiveness estimate against influenza-associated deaths in children and adolescents, while other recent studies in JAMA Network Open and Pediatrics found that annual vaccination remained effective against serious illness, hospitalisation and outpatient disease. Taken together, the studies reinforce the case for consistent yearly vaccination, even as debate continues over how strongly it should be emphasised in U.S. childhood guidance.