Households with recent birthdays were more likely to test positive for Covid in areas with high infection rates, according to an analysis of nearly 3 million households in the US.
The study, which emanates from health insurance claim data collected in the first 45 weeks of 2020 across the country, was designed to assess the potential risk of small meetings about the spread of Covid-19.
The analysis showed that in places with low Covid prevalence, there was no evidence of an increase in the infection rate in the weeks after birthdays.
But, in areas where the virus was circulating in the community, households with recent birthdays were roughly 30% more likely to have a Covid diagnosis, compared to households with no birthdays.
In other words, in counties with high Covid transmission, households with recent birthdays averaged 8.6 more cases per 10,000 people than households in the same counties without a birthday.
But the effect was even more acute when it came to a child turning a birthday, with an increase of 15.8 Covid cases per 10,000 people in the two weeks after a child’s birthday, compared to cases in families without birthday. In households with an adult birthday, the increase was an additional 5.8 cases per 10,000, according to the study published in the journal JAMA Internal Medicine.
The authors focused on birthdays as it was one of the key pieces of information that can be gleaned from insurance claims data and because it is an event where people could break Covid’s policies on meeting with other people inside, suggested study author Anupam Jena. , physician and associate professor of health policy at Harvard Medical School.
To complicate matters, the US response to the threat from the virus causing Covid-19 has not been uniform across the country, with a set of mask-wearing restrictions and policies imposing (and alleviating) local, regional, and state levels, further complicated by differences in socioeconomic, political, occupational, and ethnic diversity.
But as lead author Dr. Christopher Whaley, a policy researcher at Rand Corp, noted: “Everybody has a birthday at some point in the year.”
The authors acknowledged that they did not know whether the households had celebrated birthdays, but that the dates of birth were used as an indicator of social gatherings and in-person holidays.
In areas where there was shelter in place [stay at home] policies, Jena said they hoped there would be no “birthday effect.” However, the analysis suggested that even in such areas, the birthday effect was in line with places without such policies.
“It certainly suggests that people were not adhering to shelter-in-place policies for this particular type of event.”
The analysis also highlights that many refuge-in-place requests were directed at large formal gatherings, Whaley said. “I think it’s natural not to think that your family or friends could give you a horrible disease, so maybe let your guard down a bit.”
George is Digismak’s reported cum editor with 13 years of experience in Journalism