Joshua Salomon, Alex Reinhart, Alyssa Bilinski, Eu Chua, Wichada La Motte-Kerr, Minttu Rönn, Marissa Reitsma, Katherine Morris, Sarah LaRocca, Tamer Farag, Frauke Kreuter, Roni Rosenfeld, Ryan Tibshirani
The US COVID-19 Trends and Impact Survey: Continuous real-time measurement of COVID-19 symptoms, risks, protective behaviors, testing, and vaccination

PNAS: Proceedings of the National Academy of Sciences of the United States of America, 2021: 118, Heft 51, (article no. e2111454118)
ISSN: 0027-8424 (print), 1091-6490 (online)

The US COVID-19 Trends and Impact Survey (CTIS) is a large, cross-sectional, internet-based survey that has operated continuously since April 6, 2020. By inviting a random sample of Facebook active users each day, CTIS collects information about COVID-19 symptoms, risks, mitigating behaviors, mental health, testing, vaccination, and other key priorities. The large scale of the survey—over 20 million responses in its first year of operation—allows tracking of trends over short timescales and allows comparisons at fine demographic and geographic detail. The survey has been repeatedly revised to respond to emerging public health priorities. In this paper, we describe the survey methods and content and give examples of CTIS results that illuminate key patterns and trends and help answer high-priority policy questions relevant to the COVID-19 epidemic and response. These results demonstrate how large online surveys can provide continuous, real-time indicators of important outcomes that are not subject to public health reporting delays and backlogs. The CTIS offers high value as a supplement to official reporting data by supplying essential information about behaviors, attitudes toward policy and preventive measures, economic impacts, and other topics not reported in public health surveillance systems.