Influenza and SARS-CoV-2 Co-Infections in California, USA, September 2020–April 2021

Kyle R. Rizzo; Cora Hoover; Seema Jain; Monica Sun; Jennifer F. Myers; Brooke Bregman; Deniz M. Dominguez; Allison Jacobsen; Garrett J. Jenkins; Tamara Hennessy-Burt; Erin L. Murray


Emerging Infectious Diseases. 2021;27(11):2923-2926. 

In This Article

Abstract and Introduction


During September 1, 2020–April 30, 2021, the California Department of Public Health, Richmond, California, USA, received 255 positive influenza molecular test results that matched with severe acute respiratory syndrome coronavirus 2 molecular test results; 58 (23%) persons were co-infected. Influenza activity was minimal in California, and co-infections were sporadic.


The public health community anticipated widespread co-circulation of influenza and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes coronavirus disease (COVID-19), during the 2020–21 influenza season. However, influenza activity in California was unusually low.[1] The California Department of Public Health (CDPH; Richmond, California, USA) matched positive influenza test results with SARS-CoV-2 test results to assess the occurrence of influenza and SARS-CoV-2 co-infections in California.