| Influenza (flu) |
|---|
 |
The 2022-2023 United States flu season was notable for its early onset, high pediatric impact, and its overlap with widespread circulation of RSV and COVID-19, a cluster of viruses circulating together called the "tripledemic." Seasonal influenza activity began earlier than usual, with cases starting to rise in October 2022, and reached high nationwide levels by December 2022. [1]
During the 2022-2023 flu season, there were an estimated 31 million flu-related illness, 14 million flu-related medical visits, 360,000 flu-related hospitalizations, and 21,000 flu-related deaths. [2]
In the southeast states including Texas, Louisiana, Mississippi, Alabama, Georgia, Tennessee, and Florida experienced some of the earliest and highest activity in the country. In the south central states, Arkansas, Oklahoma, and New Mexico reported very high activity by mid-November. In the mid Atlantic area, Maryland, Virginia, Delaware, New Jersey, and Pennsylvania all saw rapid increases in November. Washington, D.C. reached very high flu levels during the early December national peak. In the northeast states, New York, Massachusetts, Connecticut, and Rhode Island experienced a sharp rise in late November. Activity peaked earlier than usual but declined steadily through January. In the Midwest, Ohio, Michigan, Indiana, Illinois, Wisconsin, and Minnesota saw a later rise compared with the South but still peaked earlier than typical seasons. Ohio and Michigan reached high activity levels in early December. In the Great Plains, lowa, Nebraska, Kansas, and the Dakotas experienced moderate-to-high activity, peaking slightly later than the national curve. North Dakota and South Dakota saw high flu levels in December. In the Mountain West, Colorado, Utah, Idaho, Montana, and Wyoming reported moderate to high activity, with peaks in December. Colorado saw one of the region's earliest increases. In the southwest, Arizona, Nevada, and California experienced high activity in late November and early December. California's activity curve was slightly flatter but still peaked early. Washington and Oregon saw high flu activity in December, with Washington reaching very high levels briefly. Activity declined more slowly than in the South. Alaska experienced a later peak, with high activity in December and January. Hawaii had a more moderate season overall, with activity rising later than the mainland. Puerto Rico and Guam reported elevated activity but with more variability due to smaller population surveillance systems. [3]
In the years before the 2022-2023 flu season, the United States had much milder flu activity than usual. During the height of the COVID-19 pandemic, people were wearing masks, staying home more often, traveling less, and washing their hands more, all of which made it harder for the flu to spread. As a result, the 2020-2021 flu season was extremely quiet, with almost no flu detected across the country. The 2021–2022 season did bring the flu back, but it was still weaker than a typical pre-pandemic season. Because those earlier seasons were so mild, the sudden, early, and intense surge of flu in 2022-2023 felt especially sharp and surprising. [4]
There were 187 pediatric flu deaths that were reported. A significant rise happened in pediatric hospitalizations and deaths in the 2022–2023 season. The season highlighted the continued importance of vaccination, as most deceased children were unvaccinated, and underscored the severity of influenza, even with other respiratory viruses circulating. [5]
The most dominant strains were by Influenza A (H3N2), with some circulation of H1N1 later in the season. Influenza B also occurred throughout the season, though it did not include the most dominant flu strains. [6] The season continued the long-term trend of B/Yamagata lineage disappearance, with no confirmed detections in the U.S., contributing to discussions about removing it from future vaccines. [7] Wastewater surveillance detected flu activity, particularly Influenza A virus, before hospitalizations peaked, acting as an early warning system for communities. [8]
The 2022-2023 influenza season in the United States was of moderate overall severity, with flu vaccines shown to reduce the risk of both moderate and severe disease across all age groups. [9] 49% of the eligible U.S. population received a flu vaccine during the 2022-2023 season. Coverage declined compared with pre-pandemic seasons and remained below national targets. Flu vaccination coverage in the U.S. for the 2022-2023 season was roughly 49-50.5% of the eligible population. [10] The composition of flu vaccines was updated for the season to better match circulating strains. For the 2022–2023 flu season, there are three flu vaccines that are preferentially recommended for people 65 years and older. There were High-Dose Quadrivalent vaccine, Flublok Quadrivalent recombinant flu vaccine and Fluad Quadrivalent adjuvanted flu vaccine. [11] CDC recommended vaccination by the end of October, consistent with previous years. [12] CDC analyzed vaccination coverage using two national surveys, NIS-Flu for children 6 months-17 years, and BRFSS for adults 18+. These surveys provided the final national coverage estimates for the season. [13] 297,255 respondents via BRFSS, surveyed Sept 2022-June 2023. Children 6 months-8 years receiving the flu vaccine for the first time needed two doses, spaced at least four weeks apart. [14] CDC and NFID held a national vaccination campaign kickoff in October 2022 to stress the importance of flu vaccination amid the expected surge in respiratory viruses. [15] Vaccination reduced the risk of flu-related E.D./urgent care visits by 48% and hospitalization by 40% overall across ages 6 months to 17 years. Broken down by age, risk reduction was greater for those age 6 months to 4 years than older children and adolescents. [16]
The 2022-2023 flu season came to a close in mid-May, when national surveillance indicators dropped to low, off-season levels and states reported that Week 20 - ending May 20, 2023 — marked the final week of the flu year. During this period, influenza activity that had surged early in the winter steadily declined as spring progressed, and by Week 20 both outpatient illness and lab-confirmed flu detections had fallen below seasonal thresholds. Public health agencies then shifted from in-season reporting to routine summer monitoring, signaling the official end of the season. [17]
