It is recommended that vaccines to protect against seasonal influenza during the 2025 influenza season include specific viral strains.
Trivalent: Egg‑based Vaccines
• an A/Victoria/4897/2022 (H1N1)pdm09‑like virus, a strain closely matching the pandemic H1N1 virus that emerged in 2009;
• an A/Croatia/10136RV/2023 (H3N2)‑like virus, a strain of the H3N2 subtype circulating in Croatia in 2023;
• a B/Austria/1359417/2021 (B/Victoria lineage)‑like virus, a strain belonging to the B/Victoria lineage of influenza B viruses.
Trivalent: Cell‑ or recombinant‑based Vaccines
• an A/Wisconsin/67/2022 (H1N1)pdm09‑like virus, a strain of the pandemic H1N1 virus similar to one circulating in Wisconsin in 2022;
• an A/District of Columbia/27/2023 (H3N2)‑like virus, a strain of the H3N2 subtype identified in the District of Columbia in 2023;
• a B/Austria/1359417/2021 (B/Victoria lineage)‑like virus, a strain from the B/Victoria lineage of influenza B viruses.
Quadrivalent (egg‑ or cell culture‑ or recombinant‑based vaccines): The above three components plus a B/Phuket/3073/2013 (B/Yamagata lineage)‑like virus, a strain from the B/Yamagata lineage of influenza B viruses.
Influenza B/Yamagata‑lineage
No B/Yamagata-lineage viruses have been detected globally since March 2020 based on the latest data from the Global Initiative on Sharing All Influenza Data (GISAID), as of August 31, 2024.
The complete absence of B/Yamagata lineage viruses suggests a very low risk of infection by these viruses. Therefore, the World Health Organization’s influenza vaccine composition advisory committee recommends that the B/Yamagata lineage component be removed from quadrivalent influenza vaccines as soon as possible. Continued surveillance through the Global Influenza Surveillance and Response System (GISRS) is crucial to identify any potential re-emergence of B/Yamagata lineage viruses.
Why were these particular strains chosen for this year’s flu vaccine?
## Flu Shots: What’s New This Year?
**Host:** Welcome back to the show. Joining us today is Dr. Emily Carter, an infectious disease specialist, to talk about the upcoming flu season. Dr. Carter, thanks for being here.
**Dr. Carter:** Thanks for having me.
**Host:** As we head into the fall and winter months, flu season is right around the corner. We’ve heard about some changes to this year’s flu vaccine. Can you tell us what’s new?
**Dr. Carter:** Absolutely. The strains of flu virus included in the vaccine are updated annually based on predictions of which strains are likely to circulate. This year, the 2024-2025 flu vaccine protects against three strains: two influenza A viruses, H1N1 and H3N2, and one influenza B virus. [[1](https://www.livescience.com/health/flu/flu-shots-have-changed-this-year-here-s-why)]
**Host:** So, why these particular strains?
**Dr. Carter:** The World Health Organization and CDC make these recommendations based on global surveillance data. They analyze which flu viruses are spreading and causing illness in different parts of the world. This helps ensure the vaccine provides the best possible protection against the strains most likely to be circulating.
**Host:**
That’s helpful information. What should our viewers know about getting the flu shot this year?
**Dr. Carter:** It’s the best way to protect yourself against the flu. Even if the vaccine doesn’t perfectly match the circulating strains, it can still reduce the severity of your illness and the risk of complications.
**Host:**
Excellent advice, Dr. Carter. Thank you for joining us and sharing your expertise
**Dr. Carter:** My pleasure.
Let’s stay healthy this flu season!