The 40 scientists who decide which flu shot you'll get

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Nov 27, 2025

Ian Barr, a leading virologist and Deputy Director at the WHO Collaborating Centre for Reference and Research on Influenza, reveals the intricate process behind flu vaccine strain selection. He shares insights on how 40 scientists meet biannually to decide which strains to target, the role of hemispheric interactions in flu patterns, and how emerging variants complicate decisions. Barr also discusses the future of vaccines, including advancements in mRNA technology, and addresses the rise of vaccine hesitancy post-COVID.

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INSIGHT

Global Panel Makes Twice-Yearly Vaccine Calls

Forty experts meet twice yearly to analyse global data, discuss zoonotic spillovers and produce rationale documents for vaccine changes.
The WHO Collaborating Centres and industry convene to explain recommendations to vaccine producers on the meeting's final day.

INSIGHT

Flu Shots Now Target Three Strains

Current vaccines contain three strains: two influenza A (H1 and H3) plus one influenza B lineage.
Since 2023 the WHO has recommended trivalent vaccines instead of the previous four-strain formulation.

INSIGHT

Strain Selection Is Crystal-Ball Work

Decisions involve uncertainty because samples arrive with delays and viruses can emerge and spread rapidly.
Ian Barr said making predictions six to nine months ahead is difficult and often involves debate among experts.

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Twice a year, 40 scientists gather together for five days to decide what strains of influenza to vaccinate against for the next flu season. It takes around six months to prepare the vaccine – which usually includes protection against three different strains of flu.

Europe and the US are heading into a flu season that some are warning could be particularly severe this winter. While even as summer approaches in Australia, the country is still registering high numbers of cases after a record-breaking flu season earlier in the year.

So how does the process of deciding on a flu vaccine each year actually work? And does what happens in the southern hemisphere influence the way the virus circulates in the northern hemisphere?

In this episode, we speak to Ian Barr, deputy director for the WHO Collaborating Centre for Reference and Research on Influenza, based at the Peter Doherty Institute for Infection and Immunity, part of the University of Melbourne. Barr is one of those 40 scientists who attend the meetings to decide what strains to focus vaccination efforts on.

This episode was produced by Mend Mariwany, Katie Flood and Gemma Ware. Mixing by Michelle Macklem and theme music by Neeta Sarl. Read the f ull credits for this episode and sign up here for a free daily newsletter from The Conversation.

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