Early data indicate flu vaccine offered significant protection
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Preliminary estimates published in MMWR and presented by the CDC indicate that this season’s influenza vaccine offered significant protection among all ages.
According to the CDC, the influenza season started early in the United States, reaching epidemic levels in October for the first time since 2009. Activity also peaked unusually early, during the week ending Dec. 3, 2022.
About 75% of infections have been caused by influenza A(H3N2), which is typically associated with more severe illness, including in children.
As of Feb. 11, there have been 111 influenza-related deaths in U.S. children this season, the most since the COVID-19 pandemic started, according to the CDC. Most of the deaths occurred in unvaccinated children.
The components of season’s vaccine appeared to be a good match for circulating influenza viruses, according to findings published in MMWR by Huong Q. McLean, PhD, MPH, a research scientist at the Marshfield Clinic Research Institute in Marshfield, Wisconsin, and colleagues.
McClean and colleagues produced estimates of influenza vaccine effectiveness from two concurrent studies conducted at the Marshfield Clinic from Oct. 23, 2022, through Feb. 10.
According to their report, the vaccine was 54% effective against medically attended outpatient acute respiratory illness caused by influenza among patients aged 6 months to 64 years. In a cohort of children, the vaccine was 71% effective against symptomatic influenza.
Adults aged 65 years and older were excluded from the test-negative, case-control study, but other preliminary data from three U.S. networks presented during a meeting of the CDC’s Advisory Committee on Immunization Practices this week provided estimates for this age group.
Data from 23 U.S. sites showed that, among all adults, the vaccine has been 43% effective this season. Vaccine effectiveness at these sites was found to be higher among adults aged 18 to 64 years (51%) than adults aged 65 years or older (35%), and it was 44% in immunocompromised adults.
Similar data were reported from EDs and urgent care centers in the West and Upper Midwest, where the vaccine was found to be 44% effective overall among all adults, including 46% effective in adults aged younger than age 65 years and 39% effective in older adults. Vaccine effectiveness among immunocompromised patients at these sites was 30%.
Hospitals in the same network reported that the vaccine was 39% effective among all adults and 29% effective among younger adults, 41% effective among older adults and 31% effective among immunocompromised patients.
According to other data submitted by seven U.S. hospitals, the adjusted vaccine effectiveness against influenza-associated hospitalization and emergency department visits among children was 49% this season, including 68% against hospitalization alone. Vaccination was more effective against influenza A(H1N1) than H3N2, 56% to 45%, data showed.
References:
CDC. FluView. https://www.cdc.gov/flu/weekly/index.htm. Updated Feb. 17, 2023. Accessed Feb. 23, 2023.
McLean HQ, et al. MMWR Morb Mortal Wkly Rep. 2023;doi:10.15585/mmwr.mm7207a1.
Pediatric flu deaths top 100 this season; most unvaccinated. https://www.cdc.gov/flu/spotlights/2022-2023/pediatric-flu-deaths.htm. Published Feb. 10, 2023. Accessed Feb. 23, 2023.
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