New analysis reveals link between birthdays and spread of COVID-19 at height of pandemic

In countries where COVID-19 infection rates are already high, birthday parties may have fueled the spread of infection during the peak months of the pandemic, according to a new analysis by researchers at the Harvard Medical School and the RAND Corporation.

The report, published on June 21 in JAMA Internal Medicine, shows that in countries with high rates of COVID-19, households with recent birthdays were 30% more likely to be diagnosed with COVID-19, compared to households without birthdays. The analysis is based on data from health insurance claims.

Researchers say they did not count the actual data birthday parties in their analysis. Instead, they used the birth dates of household members as an indicator of social gatherings and in-person festivities.

Nonetheless, the team said, the results indicate that social gatherings, such as birthday parties, may have contributed to infections during the height of the pandemic.

“These gatherings are an important part of the social fabric that unites families and society as a whole. However, as we show, in high risk areas, they can also expose households to COVID-19 infections, ”said lead study author Anupam Jena, Ruth L. Newhouse associate professor of health care policy at HMS.

With vaccination rates rising and infections falling in many parts of the country, such a retrospective analysis may seem outdated, but the results contain important clues for public health officials and individuals in the event of a new outbreak. , the scientists said.

“Our findings could help inform future action,” Jena said. “They stress the importance of understanding the types of activities that can worsen the viral spread during a pandemic and can inform political and individual decisions based on risk. The findings also quantify the potential risk of gathering with people we know. “

For more than a year from early 2020, across much of the United States, many schools were closed for in-person learning, large segments of the population worked from home, and many forms of large Formal gatherings were strictly limited, including sporting activities. events, concerts and funerals. Despite these restrictions, aimed at reducing the type of social interactions that fuel an infectious epidemic, the country has recorded more than 32 million confirmed cases of COVID-19 and nearly 600,000 deaths.

Experts have speculated that small, informal gatherings may have played a significant role in the spread of the virus, but the degree of risk associated with various types of social activity has been difficult to measure or even estimate. Without massive contact tracing and widespread diagnostic testing, it would be extremely difficult to find data linking new infections to most types of informal gatherings, the researchers said.

To get around these hurdles, Jena and her colleagues tried to unravel the relationship between social gatherings and COVID-19 by studying whether infection rates are increasing in households in which a member recently celebrated their birthday, as these occasions are often celebrated with some sort of get-together, and dates of birth are incorporated into medical records and insurance databases with COVID-19 diagnoses.

The researchers analyzed a national sample of nearly 3 million U.S. households with employer-based insurance provided by Castlight Health. In the first 45 weeks of 2020, researchers found that in counties with high COVID-19 transmission, households with recent birthdays had an average of 8.6 more cases per 10,000 people than households in the same counties. without birthday.

The magnitude of the risk varied depending on the age of the person with a birthday. In households in which a child had a birthday, the effect was even higher, with an increase in COVID-19 cases of 15.8 per 10,000 people within two weeks of a child’s birthday compared to to cases in families without birthdays. In households with an adult birthday, the increase was an additional 5.8 cases per 10,000. The researchers hypothesized that households with children’s birthdays might have been less likely to cancel their plans. birthday due to the pandemic, or that social distancing could have been followed less strictly at children’s birthday parties.

Among households in counties with low COVID-19 prevalence, the study found no increase in the rate of infection in the weeks following birthdays. The researchers also did not find that the overall link between birthdays and COVID-19 differed based on household county political leanings, or other factors such as whether it rained during anniversary week – which could have led to indoor celebrations – or if an on-site housing policy was in place in the household’s county at the time of the anniversary.

“We were only able to examine one type of event that likely leads to social gatherings, but given the magnitude of the increased risk associated with an anniversary in the household, it is clear that informal gatherings of all kinds have played a significant role in the spread of COVID-19, ”said study co-author Christopher Whaley of the RAND Corporation.