A new study, published in JAMA Internal Medicine, found a correlation between birthdays and COVID-19 infection rates.

According to the findings, households that had a recent birthday—and thus a greater likelihood of having thrown a party—in counties with a lot of cases had about a 30 percent higher risk of infection in the following two weeks, compared with households that did not have a birthday. Those celebrating a child’s birthday, the authors found, were at the highest risk of all.

“Everyone in the study was surprised at how big of an increase in risk this 30 percent seemed,” says lead author Christopher Whaley, a health policy researcher at the Rand Corporation, a nonprofit research group based in Santa Monica, Calif. “I think this really speaks to where a lot of infections came from over the last year.”
While a handful of prior studies examined the role that informal gatherings played in novel coronavirus infections, they mostly focused on one-off events, such as a single wedding reception in Maine. Whaley and his colleagues realized that birthdays could be a particularly useful tool for revealing national COVID-19 transmission patterns for a number of reasons, including the fact that every person has one and that they occur throughout the year.

Get the full story at scientificamerican.com.