How Will the Extinction of B/Yamagata Impact Global Flu Vaccination Strategies?


Drug Topics talked with Gregg Sylvester, MD, chief health officer and vice president of medical affairs at CSL Seqirus, about what we can learn from this unique situation to improve future vaccine development and distribution.

In September 2023, the WHO made a recommendation to remove the B/Yamagata influenza lineage from vaccines due to significantly lower levels of the virus in circulation. The virus has not been isolated or sequenced since March 2020, leading public health officials to believe its inclusion is no longer warranted.1 B/Yamagata’s extinction is most likely the result of public health measures—such as masking and restricted travel—implemented during the COVID-19 pandemic.2

Medical professional holding vaccine / Redpixel -

Medical professional holding vaccine / Redpixel -

Drug Topics sat down with Gregg Sylvester, MD, chief health officer and vice president of medical affairs at CSL Seqirus, to talk about what implications the extinction of B/Yamagata will have on global flu vaccination programs, the public health significance, and what we can learn from this unique situation to improve future vaccine development and distribution.

Key Takeaways

  • The WHO's surveillance system identified the decline in the B/Yamagata influenza lineage, prompting its removal from vaccines—a testament to the value of global monitoring in shaping vaccine strategies.
  • The disappearance of B/Yamagata is linked to widespread vaccination efforts and the unique circumstances of the COVID-19 pandemic. The virus's characteristics, coupled with pandemic-related measures, contributed to its decline.
  • The absence of B/Yamagata, a first for an influenza strain in vaccines, highlights the ongoing challenge of influenza. Clear communication is crucial to convey that removing it aligns with surveillance data, fostering public understanding and trust in updated vaccines.

Drug Topics: How does the WHO's global surveillance system track influenza viruses, and how did it help the FDA decide to remove the B/Yamagata strain from flu vaccines?

Gregg Sylvester, MD: The WHO has a dedicated, comprehensive and reliable surveillance system that is responsible for tracking influenza viruses worldwide. Two years before the COVID-19 pandemic, this system showed that B/Yamagata circulation was already in decline. Following the pandemic, the WHO surveillance system confirmed that there had been no B/Yamagata lineage viruses circulating since the beginning of the pandemic, March 2020.

With this confirmation and after collaborating with the WHO, the FDA directed that the B/Yamagata antigen be removed from all influenza vaccines in the U.S. as soon as possible.

Drug Topics: Can you explain how flu vaccination programs, the virus's characteristics, and the COVID-19 pandemic contributed to the decline in B/Yamagata virus?

Sylvester: The inability to find B/Yamagata is a testament to the critical role of widely implemented influenza immunization programs, amongst other contributing factors like the inherent characteristics and epidemiology of the B/Yamagata virus, which, for example, didn’t mutate as quickly as other influenza viruses and occurred more frequently in temperate climates. B/Yamagata circulation was also impacted by the unique environment created by the COVID-19 pandemic, including practices such as social distancing, masking and reduced global travel.

READ MORE: Short Animated Videos on Social Media May Help Increase Knowledge of Vaccines

Drug Topics: What can we learn from this unique situation to improve future vaccine development, distribution, and public health responses?

Sylvester: This unique situation underscores the importance of robust global surveillance systems to detect changes in virus circulation, inform vaccine strain selection, and ensure vaccines that most closely match circulating strains are manufactured to protect public health. Tracking on trends within and between different flu seasons also helps public and private entities to collaborate on public health priorities and progress immunization goals.

Drug Topics: Considering its history and impact, what is the public health significance of the B/Yamagata lineage disappearing from circulation?

Sylvester: This is the first time that an influenza strain used in all influenza vaccines, B/Yamagata, has not been detected. This is quite significant. That said, influenza infections continue to have a significant burden on public health each year. It’s vital that we improve the declining annual flu vaccination rates, so that more people can be protected, especially the very young, older adults and people with chronic diseases.

Drug Topics: How will the removal of the B/Yamagata strain impact global flu vaccination strategies, and what factors should be considered in adapting to this change?

Sylvester: As a global leader in the protection of public health, we’re closely adhering to the guidance of regulatory bodies, including the FDA and global public health authorities, to determine the optimal timelines for transitioning to trivalent influenza vaccines within each country we service. This helps ensure that we manufacture and deliver vaccines that reflect their clear directives.

Drug Topics: Why is effective communication crucial when changing vaccine formulations, like removing the B/Yamagata strain, and how can public understanding be ensured?

Sylvester: Effective and ongoing communication is essential to ensure uptake of the updated vaccine and to avoid confusion among our stakeholders. It’s important that customers and consumers understand, for example, that CSL Seqirus is aligned with the FDA’s decision and that with B/Yamagata no longer detected in circulation, removal of this strain from influenza vaccines will not impact vaccine effectiveness. Rather, it will deliver vaccines that are manufactured to match projected circulating strains.

READ MORE: Immunization Resource Center

1. The Lancet Infectious Diseases. Influenza vaccine shake-up. Lancet Infect Dis. 2023;23(12):1323. doi:10.1016/S1473-3099(23)00697-7
2. Vajo Z, Torzsa P. Extinction of the Influenza B Yamagata Line during the COVID Pandemic-Implications for Vaccine Composition. Viruses. 2022;14(8):1745. Published 2022 Aug 9. doi:10.3390/v14081745
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