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Influenza Update October 2022

The 2021-2022 influenza season was mild compared to COVID19 pre-pandemic years. The adoption of COVID19 mitigation measures probably impacted the timing and severity of influenza activity. The 2021 to 2022 flu season in the US began at its normal time in October 2021and peaked during the last week of December 2021. Influenza declined in January, as it usually does when children are out of school for the holidays, but cases did not reach a second peak until March, April, or May, depending on the region of the country. Several thousand people were hospitalized or influenza in June. Influenza activity continued to smolder for months.

Many flu seasons have only one peak, and when they have a second, it is usually due to a different influenza strain. Both peaks in 2021-2022 were due to influenza A(H3N2). Influenza cases decreased in January 2022 when Omicron cases were increasing.

Fewer flu vaccine doses were administered to adults 18 years or older in 2021-2022 than in 2020=2021. Overall, only 45.4% of US adults received a flu vaccine this past season.

The official 2022-2023 flu season started in early October and so far, case numbers were increasing earlier and at a higher rate than during the previous five flu seasons. Influenza infection rates were highest among 0- to 4-year-old children, but cases were increasing in every age group.

During its weekly update on November 4, 2022, CDC, reported a steady rise in influenza activity. Levels were highest in the Southeast and South-Central regions, followed by the Middle Atlantic and south-central West Coast regions.

The percentage of respiratory specimens that tested positive for influenza increased to 9% and the percentage of clinic visits for flulike illness rose to 4.3%, which is above the 2.5% national baseline. Testing at public health labs revealed that 66.3% of influenza A samples subtyped as H3N2, and 33.8% as H1N1.

The hospitalization rate at this point in the flu season was the highest since the 2010-2011 flu season. Most hospitalizations involved seniors and children up to age 4. Two pediatric influenza deaths have been reported and involved influenza A subtype H3N2.

Symptoms typically begin one to 4 days after exposure. Infected people are most contagious during the first 3 to 4 days after symptoms begin. Asymptomatic infected people can transmit the virus to others. Influenza virus can be detected 5 to 7 days after people become symptomatic.

Preliminary laboratory data indicates that the flu vaccine is a good match with this year’s circulating strains of influenza.


Weekly U.S. Influenza Surveillance Report, October 28, 2022,

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