Skip main navigation

Military Health System

Clear Your Cache

Health.mil has undergone a recent update. For the best user experience we recommend clearing your browser cache.

Surveillance Snapshot: Mid-Season Influenza Vaccine Effectiveness Against Laboratory-Confirmed Ambulatory Influenza Among U.S. Active Component Service Members, December 1, 2024–February 8, 2025

Image of 4CDC_Dan Higgins23224. The months of December through February constitute the period of peak activity for the annual influenza season.

This Surveillance Snapshot provides an overview of the 2024-2025 mid-season analysis of influenza vaccine effectiveness against medically-attended ambulatory influenza infections among active component U.S. service members.

A case test-negative study design was implemented among the population of active component service members from all services who were tested for influenza between December 1, 2024 and February 8, 2025—the period of peak influenza activity for the season. Data from the Defense Medical Surveillance System and standardized laboratory data provided by the Defense Centers for Public Health–Portsmouth were used for this analysis.1 Cases were defined as individuals with a positive influenza result from a rapid antigen, reverse transcription polymerase chain reaction, or culture influenza assay. Test-negative controls were individuals with a negative influenza result from a RT-PCR or culture influenza assay. Crude odds ratios were calculated, and multivariate logistic regression was used to calculate adjusted ORs (adjusted for sex, age category, any influenza vaccination in the previous five years, and month of diagnosis) and 95% confidence intervals. Estimates of VE were defined as (1 – OR) x 100.

There were 4,677 cases (4,413 A any subtype, 389 A[H3N2], 163 A[H1N1]pdm09, 274 B any subtype) and 12,787 TNC. Ten cases were both influenza A- and influenza B-positive. VE varied by influenza type (Table). Adjusted VE estimates for all influenza types and subtypes reached statistical significance. The results indicate moderate mid-season protection against influenza A(H1N1)pdm09 (adjusted VE 41%; 95% CI, 14-60) and A(H3N2) (adjusted VE 50%; 95% CI, 36-60) and low mid-season protection against influenza A (any subtype) (adjusted VE 14%; 95% CI, 5-22) and influenza B (adjusted VE 33%; 95% CI, 9-50).

The results of this analysis show low to moderate mid-season protection of the 2024-2025 seasonal influenza vaccines against medically-attended influenza A and B infections that resulted in an ambulatory care visit among ACSMs. As these estimates were obtained during the middle of the influenza season, VE estimates and confidence intervals may change when data for the full season are available and the sample sizes increase.

Authors’ Affiliation

Epidemiology and Analysis Branch, Armed Forces Health Surveillance Division, Public Health Directorate, Defense Health Agency, Silver Spring, MD: Dr. Cost, Ms. Hu

References 

  1. Rubertone MV, Brundage JF. The Defense Medical Surveillance System and the Department of Defense serum repository: glimpses of the future of public health surveillance. Am J Public Health. 2002;92(12):1900-1904. doi:10.2105/ajph.92.12.1900

You also may be interested in...

Topic
Apr 30, 2025

Medical Surveillance Monthly Report

The Medical Surveillance Monthly Report, a peer-reviewed journal launched in 1995, is the Armed Forces Health Surveillance Division's flagship publication. The MSMR provides monthly evidence-based estimates of the incidence, distribution, impact, and trends of health-related conditions among service members.

Article
Apr 25, 2025

Medical Surveillance Monthly Report "30th Anniversary" Issue Celebrates a Milestone

MSMR 30th anniversary issue celebrates a milestone

This year marks a significant milestone for the Medical Surveillance Monthly Report as we celebrate its 30th anniversary. Throughout its three decades, MSMR has continuously improved its content with the goal of providing readers with unbiased, scientifically rigorous, evidence-based medical surveillance information on the current status, trends, ...

Article
Apr 1, 2025

Guest Editorial: The Department of Defense Global Respiratory Pathogen Surveillance Program: Its Impact on Public Health, from the U.S. Armed Forces to Global Health

This editorial discusses the U.S. Department of Defense Global Respiratory Pathogen Surveillance Program, a cornerstone of U.S. Department of Defense respiratory disease surveillance, and its surveillance network of 115 active sentinel sites in addition to other participating sites, deployed locations, and partner laboratories across the globe.

Article
Mar 1, 2025

Correlation Between Mean Temperature and Incidence of Tick-borne Diseases Among Active Duty Service Members in the Contiguous U.S., 2000–2023

This study identifies the incidence of the two tick-borne diseases, Lyme disease and Rocky Mountain spotted fever, that are most frequently diagnosed within the Military Health System among active component U.S. service members and evaluates the correlation between temperature and incidence of each tick-borne disease.

Skip subpage navigation
Refine your search
Last Updated: March 28, 2025
Follow us on Instagram Follow us on LinkedIn Follow us on Facebook Follow us on X Follow us on YouTube Subscribe to updates from the MHS