In January, the CDC, the U.S. Centers for Disease Control and Prevention, took the annual flu vaccine off its schedule of recommended childhood vaccines, citing a lack of evidence for the effectiveness of flu vaccines in young children as the reason for its decision. The removal was blocked by a federal judge in March.

Parents confused by the changing advice on childhood vaccines will be encouraged by a new Harvard Medical School study.

It found that flu vaccines given to young children significantly reduce the number of childhood cases of influenza. For every 100 children vaccinated, between nine and 14 fewer children catch the flu.

Giving kids a flu vaccine every year helps keep kids in school and makes it less likely parents will miss work to stay home with a sick child.

"In the United States, that's hundreds of thousands, if not a million cases of flu that we can avoid each year," the study's senior author, Anupam Jena, said. "That's a huge effect size." Jena is the Joseph P. Newhouse Professor of Health Care Policy at Harvard Medical School and an Associate Physician in the Department of Medicine at Massachusetts General Hospital.

The findings provide additional support for the value of vaccines at a time when childhood vaccine policies in the U.S. are being scrutinized.

The Harvard study provides evidence of flu vaccines' effectiveness that had been deemed missing, Christopher Worsham, first author on the study, told TheDoctor.

When it comes to the flu vaccine, when a child is born can make a difference in their likelihood of being vaccinated. Kids born in the fall are already at the doctor for their annual checkup, so it is convenient for them to get a flu vaccine at the same time.

For kids born in the summer, getting vaccinated is less convenient. They must visit the doctor twice: once around their birthday for their checkup and again in the fall for their flu vaccine.

The study is an example of a natural experiment, a randomized clinical trial where participants are randomized by coincidence, in this case, by their birthday. The researchers looked at data from the National Health and Nutrition Examination Survey covering five flu seasons between 2016 and 2023. Because of the COVID-19 pandemic, data from the 2020-2021 and 2021-2022 flu seasons were not included in the analysis.

Vaccination rates for children born in the fall were almost nine to 13 percent higher than those for kids born during the summer months. The rates of flu diagnosis for children born in the fall were one to 1.4 percent lower.

It makes sense for parents to have children get a flu vaccine every year, Worsham said. The vaccine not only helps keep kids from missing school, which is important when they are young, it also means parents won't need to take time off from work to stay home with a sick child.

For kids born in the summer, getting vaccinated is less convenient. They must visit the doctor twice: once around their birthday for their checkup and again in the fall for their flu vaccine.

One option for parents of children born in the summer is to go to their local pharmacy for the flu vaccine in the fall and avoid the extra pediatrician visit. Some pharmacists, however, are hesitant to vaccinate young children and prefer parents take their child to the doctor.

It is worth noting that restrictions regarding pharmacists administering vaccines to young kids are loosening, Worsham, a critical care physician at Massachusetts General Hospital, explained. He suggests that parents who are involved in their kids' schools might be able to organize an in-school vaccination clinic.

Bottom line, Worsham said, “If you see a convenient flu shot opportunity take it!”

The study was published in JAMA Pediatrics.