A 3.5% decrease in COVID-19 cases in the two-week period after Thanksgiving and Christmas was recorded for US zip codes where Facebook users received advertisements consisting of short videos made by doctors and nurses urging users to stay home during the holidays, compared with that for control zip codes. The research, published in Nature Medicine, also found that the advertising campaign, which reached almost 30 million Facebook users, was associated with a significant decrease in the average distance travelled in the three days before each holiday in 2020 than in February 2020. This decrease was greater in counties that received a high intensity of advertisements (4.4%), compared to those that received fewer advertisements (3.6%).
Nurses and doctors are the most trusted health experts in the United States. However, it is unknown if these healthcare professionals can influence behavior at scale by spreading public-health messages via social media.
Esther Duflo and colleagues designed a Facebook advertising campaign to assess whether short, 20-second videos recorded by doctors and nurses sent on a massive scale would influence holiday travel at the population level, and in turn cause a decrease in COVID-19 cases after the holidays. Facebook subscribers in randomly selected zip codes in 820 counties in 13 states received these videos as sponsored content. The zip codes were chosen so that some counties were randomly assigned to receive more zip codes with videos than others. More than 11 million people received at least one ad before Thanksgiving and over 23 million received at least one video before Christmas. On average, each user included in this study received 2.6 videos at Thanksgiving and 3.5 at Christmas. The authors found that in counties in which a larger proportion of zip codes received high-coverage Facebook ads, users reduced the distance they travelled in the three days before the holidays (measured by mobile tracking data). The campaign did not, however, lead to people staying home on the day of the holiday. Overall, the authors found an average reduction of 3.5% in the number of new COVID-19 cases after the campaign.
The authors conclude that clinicians can be an effective channel for communicating life-saving information at scale through social media. Further research should investigate whether similar messages could be effective in encouraging COVID-19 vaccine uptake.
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