For every 100 children vaccinated against influenza, between nine and 14 cases are prevented, according to Harvard Medical School data.
RT’s Three Key Takeaways:
- Significant Case Reduction: A Harvard Medical School (HMS) study found that for every 100 children vaccinated against influenza, between nine and 14 cases are prevented.
- Birthday-Based Evidence: Researchers used a natural experiment based on birth months to show that children with fall birthdays have higher vaccination rates and fewer flu diagnoses than those born in the summer.
- Evidence for Policy Support: The findings provide data-driven support for pediatric influenza vaccination following recent US federal scrutiny regarding the necessity of the annual vaccine.
Pediatric influenza vaccines significantly reduce the number of childhood flu cases, according to new research from Harvard Medical School (HMS). The findings, published in JAMA Pediatrics, demonstrate that for every 100 children vaccinated, between nine and 14 fewer children catch the virus.
“In the United States, that’s hundreds of thousands, if not a million cases of flu that we can avoid each year,” said Anupam Jena, senior study author and the Joseph P Newhouse professor of healthcare policy in the Blavatnik Institute at HMS, in a news release. “That’s a huge effect size.”
The findings provide additional evidence for the effectiveness of the flu vaccine during a period of increased scrutiny regarding childhood immunizations in the US. In January, the US Centers for Disease Control and Prevention (CDC) removed the annual influenza vaccine from its recommended childhood schedule. While a US District Court blocked that change in March, researchers noted that the federal government had cited an absence of evidence for the recommendations.
“The federal government cited an absence of evidence that they want to see, and so we have provided that,” said Christopher Worsham, HMS assistant professor of medicine at Massachusetts General Hospital and first author on the study, in a news release. “We have randomized data, and it shows that flu vaccines are effective for these young children.”
The Birthday Variable
The researchers leveraged a “natural experiment” based on the timing of annual pediatric checkups. Children born in the fall typically have doctor visits scheduled when the flu vaccine is newly available for the season. In contrast, children born in the summer often have their annual appointments before the vaccine is released, requiring caretakers to schedule an additional visit.
Previous research by Jena and Worsham indicated that this additional logistical burden leads to lower vaccination rates for summer-born children. This creates two groups—more-vaccinated and less-vaccinated—based essentially on birth dates.
The study analyzed insurance claims data for children between the ages of 2 and 5 across five flu seasons between 2016 and 2023. The researchers excluded the 2020-2021 and 2021-2022 seasons due to confounding factors related to COVID-19.
Vaccination and Infection Rates
Data showed that in every season studied, fall-born children were more likely to be vaccinated and less likely to receive an influenza diagnosis. Vaccination rates for children with fall birthdays were between 8.6 and 12.5 percentage points higher than those with summer birthdays. Consequently, influenza diagnosis rates were 1.0 to 1.4 percentage points lower in the fall-born group.
“Across these five seasons, we see that for every hundred kids who are randomly vaccinated because of when their birthday falls, somewhere between nine and 14 of them avoid a case of the flu that they otherwise would have caught,” said Jena, in a news release.
The study also found no difference between the two groups regarding infection rates for illnesses without vaccines, such as the common cold or gastrointestinal viruses. The researchers noted that as children age beyond 5 years, the alignment between birthdays and doctor appointments weakens, and the differences in diagnosis rates begin to even out.
“It comes down to: vaccines work,” said Worsham.
