Opinion: Why kids with summer birthdays face surprising health risks

Both of us have kids with summer birthdays. That typically means parties organized around a few key themes: water activities, outdoor grilling and lots of ice cream. But children with summer birthdays share two other things in common: They are more likely to get the flu, and they are more likely to be diagnosed with attention deficit hyperactivity disorder.

For a characteristic we don’t get to choose, our birthdays affect many important parts of our lives. Our research has shown that there are some surprising and important considerations families and health providers alike should address for kids whose birthdays happen to be in the summer.

Take, for example, getting the flu. The Centers for Disease Control and Prevention say all children at least 6 months old should get the vaccine annually, and it typically becomes available in pediatrician’s offices at the end of August or early September. That means young children with September, October or November birthdays can easily get their flu shot when they’re already at the doctor for their annual visit, usually around their birthday.

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But what about children with summer birthdays? Because their annual check-up likely occurs before the flu shot is available in doctors’ offices, they miss this convenient opportunity to get vaccinated, and their parents are burdened with having to make an additional appointment in the fall for the shot.

In an analysis of nearly 1.1 million children aged 2 to 5 years, we showed how problematic that hassle can be. Kids with summer birthdays were significantly less likely to be vaccinated against the flu than other kids — for example, about 40% of kids with June and July birthdays received a flu shot, compared with 55% of those with October birthdays. Unsurprisingly, summer birthday kids — and older family members they’re likely to transmit illness to — were also more likely to get diagnosed with the flu.

What we do about this? If you have children with summer birthdays, it’s good to know this risk and be proactive about getting them vaccinated. Beyond awareness, though, states should reconsider policies that block pharmacies — which have better hours and more convenient locations than doctors’ offices — from giving flu vaccines to young children. School-based vaccination programs, which have increased childhood vaccination and reduced the spread of flu in communities, could also be encouraged.

Schools are the site of another challenge for kids with summer birthdays: accurate ADHD diagnosis.

A child’s birthday determines when they can enter kindergarten, and states vary on age cutoffs — some require that kids be 5 years old before Sept. 1 to enroll; others use Jan. 1 or other dates. As a result, school classes are composed of kids whose ages span as much as a year. In states with a Sept. 1 cutoff, a child born on Aug. 31 will be 364 days younger than a classmate born on Sept. 1.

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At an early age, an additional year of life is no small thing. The oldest kids in a kindergarten class could have as much as 20% more experience here on planet Earth, not to mention the accompanying physical growth, than the youngest kids. But teachers and school systems apply the same set of expectations for everyone in that class.

This setup suggests that kids who are young for their grade and are developmentally expected to be less attentive than their peers may be more likely to be diagnosed with an attention disorder. And that’s exactly what one of us found in a study analyzing more than 400,000 children living in states with a Sept. 1 cutoff for school entry. Our team showed that kids born in August were significantly more likely to be diagnosed with ADHD and treated with medication compared to kids born in September. The findings were consistent with other studies in the U.S. and in other countries where age cutoffs for school entry are common.

Again, what do we do about this? If you have a child with a summer birthday, it’s especially relevant to consider that behaviors that may otherwise reflect ADHD — inattention, fidgetiness and hyperactivity — could reflect normal development in a child who is simply young for their grade. It’s also critical that teachers and doctors keep in mind the importance of a child’s relative age to prevent students from being misdiagnosed and then improperly treated.

For both flu and ADHD, it may seem concerning that chance — something as arbitrary and random as a birthday — can have a meaningful impact on a child’s life. But it is part of life, much as blizzards cancel flights and random encounters lead to business partnerships or romantic relationships.

We can’t remove chance from our lives. But sometimes we can learn from it so we don’t become its victim — and so that having a birthday during the pool party time of year doesn’t have to be a bad thing.

Anupam B. Jena is an economist, physician and professor at Harvard Medical School, where Christopher M. Worsham is a critical care physician and public health researcher. They write the Substack newsletter Random Acts of Medicine and are the authors of “Random Acts of Medicine: The Hidden Forces That Sway Doctors, Impact Patients, and Shape Our Health,” from which this article is adapted.