WHO Updates Southern Hemisphere Flu Vaccine Strains, Replaces H1N1 and H3N2

What's Happening?

The World Health Organization (WHO) has announced changes to the influenza strains included in the Southern Hemisphere's 2026 flu vaccines. The advisory group has recommended replacing both the H1N1 and H3N2 strains used in the current vaccines. For egg-based vaccines, the new H3N2 strain will be an A/Singapore/GP20238/2024-like virus, while cell-based vaccines will use an A/Sydney/1359/2024-like virus. The influenza B Victoria lineage remains unchanged, and no recommendation was made for the B Yamagata lineage, which has not circulated since March 2020. These updates are part of the WHO's biannual review process to ensure vaccines are effective against the most prevalent flu strains.

Why It's Important?

The WHO's decision to update the flu vaccine strains is crucial for maintaining the effectiveness of influenza vaccines, which are a key tool in preventing seasonal flu outbreaks. By aligning the vaccine composition with the most current and prevalent strains, the WHO aims to enhance the vaccine's protective capabilities, potentially reducing the incidence and severity of flu cases. This update is particularly significant for the Southern Hemisphere, where flu season typically occurs from May to October. The changes also reflect ongoing efforts to monitor and respond to evolving influenza viruses, which is essential for global public health preparedness.

What's Next?

The U.S. Food and Drug Administration (FDA) is scheduled to meet on October 9 to discuss the strain selection for the Southern Hemisphere's 2026 flu vaccines. The Vaccines and Related Biological Products Advisory Committee (VRBPAC) will also make recommendations on related vaccine programs. These discussions will help determine the final composition of flu vaccines distributed in the Southern Hemisphere, ensuring they are aligned with WHO recommendations. The outcomes of these meetings will be closely watched by public health officials and vaccine manufacturers as they prepare for the upcoming flu season.