The impact of SARS-CoV-2 on reproduction rates of seasonal influenza and rsv

ABSTRACT

Background: The COVID-19 pandemic caused by SARS-CoV-2 has precipitated a global health crisis. In an effort to decrease person-to-person transmission, societal-level non-pharmacologic interventions (NPIs) to maintain social distancing have been enacted. As SARS-CoV-2 shares similar routes of transmission with other respiratory viruses, implementation of these NPIs may have decreased transmission for multiple viral pathogens. We compared influenza and respiratory syncytial (RSV) rates in prior seasons to rates during the 2019 - 2020 season at two large academic centers in Atlanta and Boston. Methods: The clinical records were queried for adults with respiratory virus testing conducted at the Emory Healthcare system and associated clinics in Atlanta and the Mass General Brigham (MGB) Healthcare System in Boston. Total cases for influenza A and B, RSV and SARS-CoV-2 were analyzed for each week of the past 5 seasons (07/01/2015-05/30/2020) for the Atlanta and Boston sites. Systematic changes in viral infection rates were calculated using viral reproduction rates, R(t), between consecutive weeks. R(t) is the ratio of the number of positive cases in one week to the number of positive cases in the previous week. We used statistical bootstrapping to determine whether R(t) for influenza and RSV were lower in 2019-2020 following the introduction of SARS-CoV-2. Analyses were conducted using R (v 4.0.0). Absolute respiratory virus activity by season, Boston (panel A) v. Atlanta (panel B) Results: For the 2019-2020 Atlanta season, R(t) < 1 (which reflects steady decline in infection rates) occurred at week 28 for influenza A, week 33 for influenza B, and week 35 for RSV, which corresponded with the increase of SARS-Cov-2 cases. The R(t) of these viruses stayed at or near 1 during weeks 33-35 in prior seasons, and R(t) was greater than 1 up to week 47. Data from MGB sites showed similar trends with a sudden decline in R(t) to < 1 at the start of the SARS-CoV-2 pandemic. Conclusion: We note decreased transmission of influenza and RSV during a time window where widespread movement restrictions and social distancing were imposed to control COVID-19. This trend was most pronounced for influenza A in Atlanta and influenza B in Boston. These data suggest that NPIs can have important effects across multiple pathogens.