JMIR Publications

ABSTRACT

Background:

Seasonal respiratory viruses had lower incidence during their 2019-2020 and 2020-2021 seasons, which overlapped with the COVID-19 pandemic. The widespread implementation of precautionary measures to prevent transmission of the SARS-CoV-2 virus have been seen to mitigate transmission of seasonal influenza as well as COVID-19. Participatory surveillance systems have historically captured mild-illnesses that are often missed by surveillance systems that rely on encounters with a healthcare provider for detection.

Objective:

This study aims to assess if a crowdsourced syndromic surveillance system captured the globally observed decrease in ILI during two influenza seasons concurrent with the COVID-19 pandemic.

Methods:

Flu Near You (FNY) is an online participatory syndromic surveillance system that allows participants in the United States and Canada to report their health information using a brief weekly survey. Reminders are sent via email to registered FNY participants to report on their own symptoms and the symptoms of household members. Non-registered participants may also report on the site. Influenza-like-illness (ILI) was defined as fever and sore throat, or fever and cough. ILI rates were determined as the number of ILI reports over the total number of reports and assessed for the 2016-2017, 2017-2018, 2018-2019, 2019-2020, and 2020-2021 influenza seasons. Self-reported influenza diagnosis and vaccination status were captured and assessed as the total number of reported events over total number of reports submitted.

Results:

ILI was detected in 3.80% (n=32,239) of the baseline season population (2016-2019), 2.58% (n=7,418) of the 2019-2020 season, and 0.27% (n=546) of the 2020-2021 season. Both influenza seasons that overlapped with the COVID-19 pandemic had lower ILI rates than the baseline seasons. ILI decline was observed during the months with widespread implementation of COVID-19 precautions in the U.S. Self-reported influenza diagnoses decreased from early 2020 through the influenza season. Self-reported influenza positivity among ILI cases varied over the observed time period. Self-reported influenza vaccination rates in FNY were high across all observed seasons.

Conclusions:

A decrease in ILI was detected in the crowdsourced FNY surveillance system during the 2019-2020 and 2020-2021 influenza seasons, which overlapped with widespread pandemic precautions, mirroring trends observed in other influenza surveillance systems. Specifically, the months within seasons that overlapped with widespread pandemic precautions observed decreases in ILI and confirmed influenza. As COVID-19 precautions lessen, monitoring for increases in influenza and other respiratory illnesses will be critical.