HealthDay News — Throughout the 2021 to 2022 influenza season, the predominant virus was influenza A(H3N2), according to research published in the July 22 issue of the US Centers for Disease Control and Prevention Morbidity and Mortality Weekly Report.

Angiezel Merced-Morales, MPH, from the CDC in Atlanta, and colleagues summarized influenza activity during the period of October 3, 2021, to June 11, 2022, in the US.

Using clinical diagnostic tests for influenza virus, clinical laboratories tested 2,850,954 respiratory specimens. The researchers found that 4.5% of these specimens tested positive: 98.6 and 1.4% for influenza A and B, respectively. Each week, the percentage of specimens testing positive varied from 0.1 to 9.9%. Public health laboratories tested 877,928 specimens, of which 2.8% tested positive: 99.5 and 0.5% for influenza A and B, respectively. Overall, 19,127 seasonal influenza A viruses were subtyped: 0.1 and 99.9% were influenza A(H1N1)pdm09 viruses and influenza A(H3N2) viruses, respectively. Influenza B lineage information was available for 41 influenza B viruses: 97.6 and 2.4% were B/Victoria lineage viruses and B/Yamagata lineage viruses, respectively. Two distinct waves were seen in influenza activity: a first wave that peaked in mid-December 2021 and a second wave with peaks ranging from mid-March to May 2022.

“Despite decreasing influenza activity in recent weeks, maintaining vigilance for influenza virus infections throughout the summer is important,” the authors write.

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