The Crick hosted scientists from across the world last week for a series of data presentations and deliberations, culminating in a decision on which influenza virus strains will be in the vaccines for the northern hemisphere this autumn. Our new video follows the work of scientists from the Worldwide Influenza Centre at the Crick in the run up to that decision.

The announcement by the World Health Organization (WHO) came after a week of discussions between members of influenza labs working with the WHO across the world, including the Worldwide Influenza Centre based at the Crick. This is the first time the meeting has been held in the UK since the network started over seventy years ago.

Each lab, known as a WHO Collaborating Centre, works throughout the year to gather information on which virus strains are circulating and whether they will respond to current vaccinations and treatments. This is critical as the flu virus is constantly changing, resulting in a need for annual top-up vaccines.

The experts gather twice a year to present their findings, propose suggestions for which strains are most prevalent, and listen to research from other areas of the globe. This results in decisions on specific vaccines for the northern and southern hemispheres.

The group also discuss zoonotic viruses like bird flu to assess current risk. They identified which vaccine viruses we need ready and waiting, to be able to produce vaccines if these viruses evolve to spread more easily to and between humans. 

The announcement at the end of the week kicked off with a summary of which strains were currently circulating, where they were distributed across the world and whether current antiviral drugs or the previous season’s vaccines worked against them.

The WHO then announced which three strains they proposed for the two types of vaccines available for manufacturers to make. They continue to recommend trivalent vaccines, which have three slots – two for A-type flu viruses and one for a B-type flu virus.

The vaccines composition in both types was the same as last year, apart from an update to one of the A viruses in both vaccines. This was to reflect that this strain has evolved and the old strain in the vaccine does not match circulating viruses as well. It is predicted that the newer virus may be prevalent in the northern hemisphere this autumn. 

The group also reported on zoonotic transmission of influenza from cows and birds, and showed whether these strains could be targeted by candidate vaccine viruses already waiting in the wings for production, or if new candidates needed to be made. This allows us to keep prepared for potential future outbreaks. 

Following last week’s decision, industrial development of the vaccines can now kick into action almost immediately. Vaccine manufacturers are primed to begin production as early as possible, ensuring that the vaccine is ready to go into arms from October 2025.

Nicola Lewis, Director of the Worldwide Influenza Centre at the Crick, said:

The virus causing flu is constantly evolving and adapting, which means we’re racing to keep up with its movements. It wouldn’t be possible to characterise which strains pose the biggest threat just from our position in the UK, we need information from across the globe to get a full picture. The week-long decision process is hard work but allows us to come to a decision collaboratively and independently of national priorities. We wouldn’t be able to do this without the international nature of science, and flu research specifically.

Wenqing Zhang, Head of WHO Global Influenza Programme, said: 

There are at least 3-5 million cases of severe seasonal influenza each year and our best armour at the moment is regular vaccination. By bringing together global experts from the Global Influenza Surveillance and Response System (GISRS) and those associated with GISRS at this meeting, we make the best possible recommendations on viruses to be included in vaccines for use in the upcoming northern hemisphere season. 

We also stay on top of avian and swine influenza virus evolution and associated risks to humans, develop new candidate vaccine viruses to support countries' prevention and control strategies, respond to avian and swine influenza outbreaks, and prepare for an influenza pandemic that might occur at any moment.