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September 17, 2020
2 min read
Interventions to prevent the transmission of SARS-CoV-2 have led to a global decline in influenza during the COVID-19 pandemic, the researchers reported in MMWR.
In addition to causing a significant drop in the percentage of respiratory samples that tested positive for influenza in the first days of the pandemic in the United States, measures such as the use of masks, social distancing, school closings and teleworking have maintained positive tests at “historically low levels between seasons,” the researchers said. The southern hemisphere has experienced a similar effect.
The number of laboratory samples that tested positive for influenza reached an all-time low following COVID-19 mitigation efforts.
Credit: CDC
If measures continue into the fall, the flu season in the US “could be shortened or delayed,” according to the report.
“The global decline in influenza virus circulation appears to be real and concurrent with the COVID-19 pandemic and its associated community mitigation measures.” Sonja J. Olsen, PhD, wrote an epidemiologist with the CDC’s Division of Influenza and his colleagues.
Olsen and his colleagues reviewed data from about 300 US laboratories in all 50 states, Puerto Rico, Guam, and the District of Columbia. They also analyzed influenza laboratory data from surveillance platforms in Australia, Chile, and South Africa to determine viral activity in the southern hemisphere.
Results showed that the percentage of respiratory samples that tested positive for influenza dropped from more than 20% to 2.3%, and interstate levels also remained low: 0.2% versus 1% to 2% in seasons. previous. In the Southern Hemisphere, there were only 33 positive influenza tests out of 60,031 Australian specimens, 12 out of 21,178 Chilean specimens, and six out of 2,098 South African specimens from April to July – a .06% positivity rate (95% CI, .04% – 0.08%). By comparison, 13.7% of samples from the southern hemisphere tested positive for influenza during the same period in 2017, 2018, and 2019.
“Initially, decreases in influenza virus activity were attributed to decreased testing, because people with respiratory symptoms were often referred preferentially for SARS-CoV-2 evaluation and testing,” wrote Olsen and his colleagues. “However, renewed efforts by public health officials and physicians to test samples for influenza resulted in an adequate number of tests and the detection of little or no influenza viruses.
“In addition, some countries, such as Australia, had less stringent criteria for testing respiratory samples than in previous seasons and tested markedly more samples for influenza, but still detected few with positive results during the months when influenza epidemics in the southern hemisphere they tend to peak. “
Experts have raised concerns about the possibility of a severe flu season occurring at the same time as the COVID-19 pandemic.
“In light of the novelty of the COVID-19 pandemic and the uncertainty of ongoing community mitigation measures, it is important to plan for the seasonal flu circulation this fall and winter,” the researchers wrote. “Flu vaccination for all people 6 months and older remains the best method for preventing flu and is especially important this season, when SARS-CoV-2 and the flu virus can co-circulate.”
Perspective
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Amesh A. Adalja, MD
Because influenza and COVID-19 are similarly transmitted, it is not surprising that community mitigation activities for one have an impact on the other. This is clearly demonstrated in data from the most recent flu season in the United States, during which COVID-19 mitigation basically disrupted the flu season earlier. The current dramatically lower flu season in the southern hemisphere provides further evidence of this phenomenon and has likely significantly decreased the global circulation of seasonal flu viruses. Since these measures keep flu at bay and will (hopefully) be combined with high flu vaccination rates, the Northern Hemisphere flu season may be significantly shortened, leaving more capacity to deal with COVID-19.
Amesh A. Adalja, MD
Senior scholar
Johns Hopkins Center for Health Security
Disclosures: Adalja does not report relevant financial disclosures.
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