Influenza activity decreased in March 2020, remained low through May 2021; decrease seen in other viruses, with no increase until Spring 2021
FRIDAY, July 23, 2021 (HealthDay News) — Circulation of respiratory viruses, including influenza and respiratory syncytial virus, was low during the COVID-19 pandemic, according to research published in the July 23 issue of the U.S. Centers for Disease Control and Prevention Morbidity and Mortality Weekly Report.
Sonja J. Olsen, Ph.D., from the CDC in Atlanta, and colleagues describe changes in influenza and other respiratory virus activity during the COVID-19 pandemic.
The researchers note that influenza activity decreased in March 2020 in the United States, was historically low through the summer of 2020, and remained low during October 2020 to May 2021. In early 2020, there were also decreases seen in circulation of other respiratory pathogens, including respiratory syncytial virus, common human coronaviruses types OC43, NL63, 229E, and HKU1, and parainfluenza viruses types 1 to 4, which did not increase until spring 2021. There was a decrease observed in human metapneumovirus circulation in March 2020, which remained low through May 2021. Throughout 2020 and as of early May 2021, respiratory adenovirus circulated at lower levels. In March 2020, rhinovirus and enterovirus circulation decreased, remained low until May 2020, and subsequently increased to near prepandemic seasonal levels.
“Clinicians should be aware that respiratory viruses might not exhibit typical seasonal circulation patterns and that a resumption of circulation of certain respiratory viruses is occurring,” the authors write. “Improved understanding of the role that nonpharmaceutical interventions play on the transmission dynamics of respiratory viruses can guide future prevention recommendations.”
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