Trivalent Influenza Vaccines

About trivalent flu vaccines

Trivalent flu vaccines protect against three different influenza viruses. Trivalent flu vaccines in the United States include vaccine viruses or viral proteins from one influenza A(H1N1) virus, one influenza A(H3N2) virus, and one influenza B/Victoria lineage virus.

Quadrivalent to trivalent flu vaccine transition

Quadrivalent flu vaccines include vaccine viruses or viral proteins from four viruses: one influenza A(H1N1) virus, one influenza A(H3N2) virus, one influenza B/Victoria lineage virus and one B/Yamagata lineage virus. They differ from trivalent flu vaccines because two influenza B viruses are represented in the vaccine (one from each lineage). Trivalent flu vaccines include three vaccine viruses, with only one influenza B virus. They do not include an influenza B/Yamagata lineage vaccine virus or viral protein component. Beginning with the 2024-2025 flu season, the influenza B/Yamagata vaccine component in U.S. flu vaccines was removed because influenza B/Yamagata viruses have not been detected by global flu surveillance after March 2020. Because B/Yamagata viruses are not actively circulating in people, the risk of infection with B/Yamagata lineage viruses is considered to be low at this time. A variety of data and criteria were used to make the vaccine recommendations.

Past use of trivalent flu vaccines

Flu vaccines have been used for more than 50 years in the United States. The composition of U.S. flu vaccines is reviewed annually, and is updated for most seasons. Over the years, the number of flu vaccine virus components in U.S. flu vaccines has varied, but U.S. seasonal flu vaccines were trivalent from 1978-1979 through 2012-2013. During those 35 seasons, flu vaccines included three components: one influenza A(H1N1), one influenza A(H3N2), and one influenza B (either from the B/Yamagata or B/Victoria lineage).

Previous transition from trivalent to quadrivalent vaccines

The U.S. began to transition to quadrivalent flu vaccines during the 2013-2014 flu season. This was done to incorporate a fourth component—from a second influenza B virus—in U.S. flu vaccines to protect against both lineages of influenza B viruses (B/Yamagata lineage and B/Victoria lineage). At the time, both lineages of B viruses were circulating in people, and data indicated there was little cross-protection between the two lineages of B viruses. That meant that vaccination against one lineage of B virus might not protect against the other lineage. By the 2021-2022 flu season, all flu vaccines available in the United States were quadrivalent. However, because influenza B/Yamagata lineage viruses have not been detected after March 2020, the World Health Organization (WHO) and FDA's Vaccines and Related Biological Products Advisory Committee (VRBPAC) recommended that the influenza B/Yamagata lineage component be excluded from flu vaccines as soon as possible. During the March 2024 FDA VRBPAC meeting, FDA announced that only trivalent flu vaccines would be available for use in the United States for the 2024-2025 flu season. As of the 2026 Southern Hemisphere VCM there will no longer be updated recommendations for the B/Yamagata lineage component.

Who can get trivalent flu vaccine

Everyone 6 months and older should get annual flu vaccination. All flu vaccines for use in the United States for the 2025-2026 season will be trivalent. Different flu vaccines are approved for different age groups.

Who shouldn’t get trivalent flu vaccine

Trivalent flu vaccines are contraindicated for some people who had a severe allergy to a previous dose of flu vaccine or to an ingredient in the flu vaccine. There is no specific contraindication for flu vaccine based on the number of components in the vaccine (trivalent or quadrivalent); however, different flu vaccines are approved for use in people in different age groups. In addition, some flu vaccines are not recommended for certain groups of people, such as people younger than 65 years. A person’s age and health status are factors to consider when deciding on which kind of flu vaccine to receive.

Availability of trivalent vaccines this season

All flu vaccines for the 2025-2026 season are trivalent in the United States. Projections on U.S. flu vaccine supply are available.

Trivalent flu vaccines safety

Trivalent U.S. flu vaccines used from 1978-1979 through 2020-2021 had an excellent safety record. There are no safety concerns regarding the transition from quadrivalent vaccines back to trivalent flu vaccines. However, as always, flu vaccines will be monitored closely for safety and effectiveness.

B/Yamagata virus detections

There have been no confirmed detections of influenza B/Yamagata lineage viruses after March 2020. Reports of B/Yamagata detections after March 2020 for which samples were available were confirmed as naturally occurring B/Victoria lineage viruses or were identified as the B/Yamagata lineage component of live attenuated vaccines (i.e., nasal spray flu vaccines). However, it is not known whether influenza B/Yamagata lineage viruses are extinct at this time.

The Global Influenza Surveillance and Response System (GISRS), a global system of public health institutions coordinated by WHO, continue to conduct surveillance and detections of influenza B/Yamagata lineage viruses are sent into Collaborating Centers for further analysis.

If B/Yamagata viruses begin spreading again

Flu viruses are always changing. This is the main reason why the composition of flu vaccines is assessed annually and is updated for most seasons. CDC and GISRS will continue to conduct surveillance for influenza B/Yamagata lineage viruses. If the situation changes, CDC, FDA, and flu vaccine manufacturers will adapt accordingly.