Researchers have struggled to measure the impact of private gatherings on the spread of the coronavirus, but scientists from Harvard, the Rand Corporation and Castlight Health hit on a creative method for pulling back the curtain. Using health insurance claims data, they found that in areas where the virus was widespread, the covid risk in families increased by nearly a third in the two weeks after a family member’s birthday. The effect was even more pronounced when the birthday was that of a child and was the same in both Republican and Democratic areas of the country.
