Child flu vaccines significantly reduce the number of illnesses in children, protecting up to a million young people each year, according to new research from Harvard Medical School. The findings underscore the public health benefits of vaccines at a time when vaccine hesitancy, fueled by misinformation and the anti-vaccine movement, has driven an increase in deadly and preventable diseases, including a resurgence of measles.
Key Findings from the Study
For every 100 children aged 2 to 5 who receive the flu shot or nasal spray, there are between 9 and 14 fewer cases of influenza. Anupam Jena, the Joseph P. Newhouse Professor of Health Care Policy at Harvard's Blavatnik Institute, stated in a Monday release: "In the United States, that's hundreds of thousands, if not a million cases of flu that we can avoid each year. That's a huge effect size."
The analysis compared flu vaccination and diagnosis rates in young children born at different times of the year, using national insurance claims data from 2016 to 2023 (excluding 2020-2022 due to the Covid-19 pandemic). Children with fall birthdays were more likely to be vaccinated, with rates 8.6 to 12.5 percent higher than those with summer birthdays. This is because young children typically have an annual doctor visit around their birthday, and flu vaccines are released in the fall, making it convenient for fall-born children. Summer-born children often need an additional appointment, leading to lower vaccination rates.
Impact of Vaccine Hesitancy
Vaccine hesitancy has contributed to years of lowered vaccination rates, resulting in a record number of child flu deaths during the 2024-2025 season. Nearly 90 percent of child flu deaths in the previous season and 85 percent this year occurred in children who were not fully vaccinated, researchers reported. The U.S. Centers for Disease Control and Prevention (CDC) also removed recommendations for annual flu vaccines earlier this year, a move later blocked by a U.S. District Court.
Christopher Worsham, an assistant professor of medicine at Massachusetts General Hospital, commented: "The federal government cited an absence of evidence that they want to see, and so we have provided that. We have randomized data, and it shows that flu vaccines are effective for these young children."
Vaccine Effectiveness and Public Health Benefits
While seasonal vaccine effectiveness varies each year, getting vaccinated reduces the risk of illness and severe outcomes in children. The CDC estimates that flu vaccination prevented 10 million illnesses and 12,000 deaths across all age groups during the 2024-2025 flu season. The agency states: "The most recent data indicate that flu vaccination reduced the risk of flu-related death by more than 75 percent among children with underlying, higher risk medical conditions and by more than 85 percent among healthy children."
The 2025-2026 flu season has seen a fraction of the deaths compared to the previous season, though deaths from the prior season continued to be reported earlier this year. The Harvard researchers emphasize that their findings provide crucial evidence supporting the effectiveness of flu vaccines in protecting young children.
