DoD Surveillance: Low to Moderate Effectiveness for Flu Vaccine

A mid-season analysis of the influenza vaccine by the US Department of Defensive (DoD) Global Respiratory Pathogen Surveillance Program (DoDGRPSP) has reported low to moderate vaccine effectiveness (VE). 

The study included 295 Military Health System (MHS) beneficiaries (adults and children) who tested positive for influenza and 965 controls who tested negative. Vaccinated patients had received the 2024-2025 influenza vaccine at least 14 days prior to symptom onset. The study conducted VE analyses for influenza A (any subtype), influenza A(H1N1)pdm09, and influenza A(H3N2). 

Overall, moderate effectiveness against influenza A(H1N1)pdm09 was reported in all beneficiaries and children aged 6 months to 17 years. In adults aged 18 to 64 years—and all beneficiaries—there was moderate effectiveness against influenza A(H3N2). VE estimates against influenza A (any subtype) for all beneficiaries, children, and adults were not significant; VE estimates were also not effective among children for influenza A(H3N2) and in adults for influenza A(H1N1)pdm09.

Adjusted VE estimates among all participants for influenza A (any subtypes), influenza A(H1N1)pdm09, and influenza A(H3N2) were 25%, 58%, and 42%, respectively. VE for influenza B was not calculated due to a low number of cases.

Flu vaccination rates for adults are usually in the 30% to 60% range despite the recommended target of 70%. Flu vaccination rates were rising by around 1% to 2% annually before 2020, but began dropping after the COVID-19 pandemic, especially in higher-risk groups. In adults aged ≥ 65 years, flu vaccination rates dropped from 52% in 2019-2020 to 43% in 2024-2025.

According to the Centers for Disease Control and Prevention (CDC), at the end of the 2023-2024 flu season, 9.2 million fewer doses were administered in pharmacies and doctors offices compared with the baseline before the COVID-19 pandemic. Since 2022, private manufacturers have distributed significantly fewer influenza vaccine doses. 

Each March, the US Food and Drug Association (FDA) Vaccines and Related Biological Products Advisory Committee (VRBPAC) meets to analyze the current influenza season and forecast the next. The committee reviews and discusses data on influenza strain circulation and VE, which come from DoDGRPSP analyses. In February, US Department of Health and Human Services officials indefinitely postponed a public meeting of the CDC Advisory Committee on Immunization Practice (ACIP), at which members were also expected to discuss, among other things, VE and vaccine recommendations. The FDA canceled a March 13 VRBPAC meeting and provided no reason for the cancelation to members. That day, however, the FDA issued new recommendations for the influenza vaccine for the 2025-2026 season without the input of VRBPAC. Instead, experts from the FDA, CDC, and DoD made recommendations after reviewing surveillance data from the US and globally.

For the 2025-2026 influenza season, the FDA recommends the vaccines be trivalent and target 2 strains of influenza A and 1 strain of influenza B. The FDA anticipates there will be an “adequate and diverse supply” of approved trivalent seasonal influenza vaccines. Trivalent flu vaccines are formulated to protect against 3 influenza viruses: an A(H1N1) virus, an A(H3N2) virus, and a B/Victoria virus. All influenza vaccines for the 2025-2026 season are anticipated to be trivalent in the US.

A mid-season analysis of the influenza vaccine by the US Department of Defensive (DoD) Global Respiratory Pathogen Surveillance Program (DoDGRPSP) has reported low to moderate vaccine effectiveness (VE). 

The study included 295 Military Health System (MHS) beneficiaries (adults and children) who tested positive for influenza and 965 controls who tested negative. Vaccinated patients had received the 2024-2025 influenza vaccine at least 14 days prior to symptom onset. The study conducted VE analyses for influenza A (any subtype), influenza A(H1N1)pdm09, and influenza A(H3N2). 

Overall, moderate effectiveness against influenza A(H1N1)pdm09 was reported in all beneficiaries and children aged 6 months to 17 years. In adults aged 18 to 64 years—and all beneficiaries—there was moderate effectiveness against influenza A(H3N2). VE estimates against influenza A (any subtype) for all beneficiaries, children, and adults were not significant; VE estimates were also not effective among children for influenza A(H3N2) and in adults for influenza A(H1N1)pdm09.

Adjusted VE estimates among all participants for influenza A (any subtypes), influenza A(H1N1)pdm09, and influenza A(H3N2) were 25%, 58%, and 42%, respectively. VE for influenza B was not calculated due to a low number of cases.

Flu vaccination rates for adults are usually in the 30% to 60% range despite the recommended target of 70%. Flu vaccination rates were rising by around 1% to 2% annually before 2020, but began dropping after the COVID-19 pandemic, especially in higher-risk groups. In adults aged ≥ 65 years, flu vaccination rates dropped from 52% in 2019-2020 to 43% in 2024-2025.

According to the Centers for Disease Control and Prevention (CDC), at the end of the 2023-2024 flu season, 9.2 million fewer doses were administered in pharmacies and doctors offices compared with the baseline before the COVID-19 pandemic. Since 2022, private manufacturers have distributed significantly fewer influenza vaccine doses. 

Each March, the US Food and Drug Association (FDA) Vaccines and Related Biological Products Advisory Committee (VRBPAC) meets to analyze the current influenza season and forecast the next. The committee reviews and discusses data on influenza strain circulation and VE, which come from DoDGRPSP analyses. In February, US Department of Health and Human Services officials indefinitely postponed a public meeting of the CDC Advisory Committee on Immunization Practice (ACIP), at which members were also expected to discuss, among other things, VE and vaccine recommendations. The FDA canceled a March 13 VRBPAC meeting and provided no reason for the cancelation to members. That day, however, the FDA issued new recommendations for the influenza vaccine for the 2025-2026 season without the input of VRBPAC. Instead, experts from the FDA, CDC, and DoD made recommendations after reviewing surveillance data from the US and globally.

For the 2025-2026 influenza season, the FDA recommends the vaccines be trivalent and target 2 strains of influenza A and 1 strain of influenza B. The FDA anticipates there will be an “adequate and diverse supply” of approved trivalent seasonal influenza vaccines. Trivalent flu vaccines are formulated to protect against 3 influenza viruses: an A(H1N1) virus, an A(H3N2) virus, and a B/Victoria virus. All influenza vaccines for the 2025-2026 season are anticipated to be trivalent in the US.

A mid-season analysis of the influenza vaccine by the US Department of Defensive (DoD) Global Respiratory Pathogen Surveillance Program (DoDGRPSP) has reported low to moderate vaccine effectiveness (VE). 

The study included 295 Military Health System (MHS) beneficiaries (adults and children) who tested positive for influenza and 965 controls who tested negative. Vaccinated patients had received the 2024-2025 influenza vaccine at least 14 days prior to symptom onset. The study conducted VE analyses for influenza A (any subtype), influenza A(H1N1)pdm09, and influenza A(H3N2). 

Overall, moderate effectiveness against influenza A(H1N1)pdm09 was reported in all beneficiaries and children aged 6 months to 17 years. In adults aged 18 to 64 years—and all beneficiaries—there was moderate effectiveness against influenza A(H3N2). VE estimates against influenza A (any subtype) for all beneficiaries, children, and adults were not significant; VE estimates were also not effective among children for influenza A(H3N2) and in adults for influenza A(H1N1)pdm09.

Adjusted VE estimates among all participants for influenza A (any subtypes), influenza A(H1N1)pdm09, and influenza A(H3N2) were 25%, 58%, and 42%, respectively. VE for influenza B was not calculated due to a low number of cases.

Flu vaccination rates for adults are usually in the 30% to 60% range despite the recommended target of 70%. Flu vaccination rates were rising by around 1% to 2% annually before 2020, but began dropping after the COVID-19 pandemic, especially in higher-risk groups. In adults aged ≥ 65 years, flu vaccination rates dropped from 52% in 2019-2020 to 43% in 2024-2025.

According to the Centers for Disease Control and Prevention (CDC), at the end of the 2023-2024 flu season, 9.2 million fewer doses were administered in pharmacies and doctors offices compared with the baseline before the COVID-19 pandemic. Since 2022, private manufacturers have distributed significantly fewer influenza vaccine doses. 

Each March, the US Food and Drug Association (FDA) Vaccines and Related Biological Products Advisory Committee (VRBPAC) meets to analyze the current influenza season and forecast the next. The committee reviews and discusses data on influenza strain circulation and VE, which come from DoDGRPSP analyses. In February, US Department of Health and Human Services officials indefinitely postponed a public meeting of the CDC Advisory Committee on Immunization Practice (ACIP), at which members were also expected to discuss, among other things, VE and vaccine recommendations. The FDA canceled a March 13 VRBPAC meeting and provided no reason for the cancelation to members. That day, however, the FDA issued new recommendations for the influenza vaccine for the 2025-2026 season without the input of VRBPAC. Instead, experts from the FDA, CDC, and DoD made recommendations after reviewing surveillance data from the US and globally.

For the 2025-2026 influenza season, the FDA recommends the vaccines be trivalent and target 2 strains of influenza A and 1 strain of influenza B. The FDA anticipates there will be an “adequate and diverse supply” of approved trivalent seasonal influenza vaccines. Trivalent flu vaccines are formulated to protect against 3 influenza viruses: an A(H1N1) virus, an A(H3N2) virus, and a B/Victoria virus. All influenza vaccines for the 2025-2026 season are anticipated to be trivalent in the US.