Influenza Activity and Composition of the 2022-23 Influenza Vaccine - United States, 2021-22 Season

Abstract

Before the emergence of SARS-CoV-2, the virus that causes COVID-19, influenza activity in the United States typically began to increase in the fall and peaked in February. During the 2021-22 season, influenza activity began to increase in November and remained elevated until mid-June, featuring two distinct waves, with A(H3N2) viruses predominating for the entire season. This report summarizes influenza activity during October 3, 2021-June 11, 2022, in the United States and describes the composition of the Northern Hemisphere 2022-23 influenza vaccine. Although influenza activity is decreasing and circulation during summer is typically low, remaining vigilant for influenza infections, performing testing for seasonal influenza viruses, and monitoring for novel influenza A virus infections are important. An outbreak of highly pathogenic avian influenza A(H5N1) is ongoing; health care providers and persons with exposure to sick or infected birds should remain vigilant for onset of symptoms consistent with influenza. Receiving a seasonal influenza vaccine each year remains the best way to protect against seasonal influenza and its potentially severe consequences.

FIGURE 1

Influenza-positive test results reported by clinical laboratories to CDC, by MMWR week and influenza season — United States, October–June, 2017–18 to 2021–22

FIGURE 2

Weekly rate of hospitalizations among patients of all ages with laboratory-confirmed influenza — United States, October–June, 2011–12 and 2015–16 to 2021–22 * Weekly rates for all seasons before the 2021–22 season reflect end-of-season rates. For the 2021–22 season, rates for recent hospital admissions are subject to reporting delays. As hospitalization data are received each week, case counts and rates are updated accordingly. Because of late season activity during the 2021–22 season, the Influenza Hospitalization Surveillance Network has extended surveillance beyond the typical end date of April 30 (MMWR week 17).