Trivalent Influenza Vaccines
What is a trivalent influenza (flu) vaccine?
Trivalent flu vaccines protect against three different influenza viruses. Trivalent flu vaccines in the United States will include vaccine viruses or viral proteins from one influenza A(H1N1) virus, one influenza A(H3N2) virus, and one influenza B/Victoria lineage virus.
What is the difference between quadrivalent and trivalent flu vaccines?
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. Trivalent flu vaccines include three vaccine viruses. They will not include an influenza B/Yamagata lineage vaccine virus or viral protein component.
Why is the United States transitioning from quadrivalent to trivalent flu vaccines?
The influenza B/Yamagata vaccine component in flu vaccines is being removed because influenza B/Yamagata viruses have not been detected after March 2020, using global surveillance for actively circulating influenza viruses.
What is the timeline of the transition from quadrivalent to trivalent flu vaccines?
All U.S. flu vaccines will be trivalent for the 2024-2025 season.
Has the United States had trivalent flu vaccines in the past?
Yes. 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 changes for most seasons. Over the years, the number of flu vaccine virus components has varied in U.S. flu vaccines, 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) virus, one influenza A(H3N2) virus, and one influenza B virus (either from the B/Yamagata or B/Victoria lineage).
Why did the United States transition from trivalent to quadrivalent flu vaccines?
The U.S. transitioned to quadrivalent flu vaccines during the 2013-2014 flu season. This was done to incorporate a fourth component—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 would 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 vaccine virus 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.
Who can get trivalent flu vaccine?
All flu vaccines for use in the United States for the 2024-2025 season will be trivalent. Everyone 6 months and older should get an annual flu vaccine, but different vaccines are approved for different age groups.
Who shouldn’t get trivalent flu vaccine?
There is no specific contraindication for flu vaccine based on the number of components in the vaccine; 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. Factors that can determine a person’s suitability for flu vaccine include a person’s age and health status. More information is available at Who Should and Who Should NOT get a flu vaccine.
How much trivalent flu vaccine will be available for the United States during the 2024-2025 flu season?
All flu vaccines for the 2024-2025 season are anticipated to be trivalent in the United States. Projections on U.S. flu vaccine supply for the upcoming season will come from flu vaccine manufacturers at a later time.
Are trivalent flu vaccines safe?
Yes. Trivalent U.S. flu vaccines used from 1978-1979 through 2012-2013 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.
Background on the removal of the B/Yamagata lineage vaccine component
When was the last time that B/Yamagata lineage influenza viruses were detected, and are there risks of infection currently?
CDC and global influenza virus surveillance data show that B/Yamagata lineage influenza viruses have not been detected 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. More information is available at Recommended composition of influenza virus vaccines for use in the 2024-2025 northern hemisphere influenza season.
Are influenza B/Yamagata lineage viruses now extinct?
There have been no confirmed detections of influenza B/Yamagata lineage viruses after March 2020. Reports of B/Yamagata detections after March 2020 with available samples 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, will continue to conduct targeted surveillance for influenza B/Yamagata lineage viruses.
What happens if B/Yamagata viruses return after the component is removed from the vaccine?
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 WHO will continue to actively conduct targeted surveillance for influenza B/Yamagata lineage viruses. If the situation changes, CDC, FDA, and flu vaccine manufacturers will adapt accordingly. However, since there have been no confirmed actively circulating influenza B/Yamagata viruses in global surveillance after March 2020, the inclusion of a B/Yamagata antigen is no longer warranted at this time.
