A study discovered the fascinating reason why kids born in the summer are more likely to get the flu—and other ripple effects caused by that

If you have a kid born in the summer months and you’ve noticed they come down with a winter flu infection more often than other kids, you’re probably right—and you’re not alone. Researchers Bapu Jena and Chris Worsham both noticed struggles they had with their summer-born kids and scheduling flu shots, so they decided to study it. They shared their findings on the Freakonomics podcast, where they also talked to other doctors and public health experts about why American kids with summer birthdays are more likely to get sick from the flu—and the far-reaching effects of that from a public health standpoint.

The basic gist is this: Most young kids get a yearly checkup around their birthday. And when your kid has a summer birthday, that means flu shots aren’t ready yet when they go in for their checkup, and it’s a hassle to schedule another appointment just a few weeks or months later to get a vaccine. Hassle = many parents won’t do it, but even those who do try to make the appointment run into unexpected roadblocks: Pediatricians book up quickly, and pharmacies often don’t offer the shots to really young kids. Jena and Worsham found that this results in about a third fewer kids who were born in the summer months getting their yearly flu shot—and, as a result, they have about a 15 percent higher chance of actually getting the flu.

But it’s important to note that this data is based on things like medical and insurance records, meaning the flu infections Jena and Worsham included in their study were those severe enough to warrant medical care. And that’s what’s important about this data, they say. Many kids who catch the flu don’t get that sick—but many do, as shown by this study. And what’s worse is that the flu is highly transmissible, and for all these sick kids, there are other people they infected. They may have gotten severely sick, too. Some of them likely even died.

So even though it’s a hassle, summer kids need flu shots, too. But this doesn’t just fall on parents. What we need is better medical infrastructure that makes vaccines more widely available in more places so all people can get vaccinated as easily as possible.

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