WHO excludes rare flu type from 2024 vaccines

30.09.2023 posted by Admin

A shift in flu vaccine strategies for 2024

When the World Health Organization (WHO) recently made its recommendations for next year's flu vaccines, they made an interesting move. They decided to exclude a group of viruses that hasn't been seen since the early days of the Covid-19 pandemic.

Back in 2020, as Covid-19 was spreading rapidly, people took various precautions like wearing masks, washing hands, and keeping their distance from others. A surprising side effect of these measures was a sharp decline in cases of the flu. However, as time passed, the flu made a comeback, but one group of flu viruses, called influenza B/Yamagata, did not resurface, suggesting it might have disappeared altogether.

Looking ahead to the 2024 Southern Hemisphere flu season, the experts advising the WHO recommended trivalent vaccines, which focus on three types of flu. These include two influenza A strains, H1N1 and H3N2, and an influenza B/Victoria strain. Quadrivalent vaccines, which cover four types of flu, can still target a component of the B/Yamagata lineage.

In a press conference, WHO advisors explained that since no cases of B/Yamagata infections had been reported for years, there was no need to include it in the vaccines anymore. David Wentworth, the director of the Collaborating Centre for Surveillance, Epidemiology, and Control of Influenza at the US Centers for Disease Control and Prevention, clarified that it's not necessarily a bad thing to have it in the vaccine, but it's no longer necessary.

Flu vaccines are constantly updated because the viruses keep evolving. The WHO's recommendations serve as a guideline for regulators and manufacturers worldwide, but individual countries make the final decisions about which components to include in their vaccines. These recommendations for the Southern Hemisphere are typically issued in September, allowing enough time for regulatory approval, production, and distribution ahead of the flu season. Recommendations for the Northern Hemisphere are made in February.

In their report on the 2024 Southern Hemisphere flu vaccine recommendations, WHO's advisors also considered the "theoretical risk of reintroduction into the population" if B/Yamagata viruses were used in vaccine manufacturing. This potential risk can be minimized by excluding B/Yamagata from the vaccines, as explained by Kanta Subbarao, director of the WHO Collaborating Centre for Reference and Research on Influenza at the Peter Doherty Institute for Infection and Immunity in Australia.

Currently, the flu vaccines administered in the United States for the ongoing flu season are quadrivalent vaccines, covering two influenza A viruses (H1N1 and H3N2) and two influenza B viruses, including one from the Yamagata lineage. Evidence from the previous Southern Hemisphere season suggests that these vaccines are a good match for the viruses circulating this fall and winter.

The WHO advisors stressed that flu vaccines remain safe and effective, regardless of the specific formulation a country uses. While there is ongoing discussion within the US Food and Drug Administration (FDA) about potentially shifting to trivalent vaccines for future flu seasons, such a change would require careful consideration due to licensing and manufacturing requirements.

The FDA's vaccine advisory committee is scheduled to convene on October 5 to discuss recommendations for flu vaccines to be offered in the Southern Hemisphere in 2024.
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