Why scientists are so excited about a nasal spray vaccine for bird flu

A new nasal spray vaccine for H5N1 bird flu has shown promising early results, raising hopes it could one day be used to help curb a future pandemic.

Testing found that the bird flu vaccine, administered as a spray in each nostril, generated a “strong immune response” in rodents during an early-stage trial run by scientists at Washington University School of Medicine, in the US state of Missouri.

While traditional flu vaccines, delivered by injection, are highly effective at preventing serious illness, there is still between a 40 and 60 per cent chance that a vaccinated person can become infected and silently pass the flu virus on to others.

Nasal vaccines, however, stop a virus from establishing itself in the nose and lungs – the sites where flu viruses first infect and replicate – meaning they also prevent onward transmission.

“Delivering vaccines directly to the upper airway – where you most need protection from respiratory infection – could disrupt the cycle of infection and transmission. That’s crucial to slowing the spread of infection for H5N1,” said Dr Michael Diamond, Professor of Molecular Microbiology at Washington University and co-author of the study.

The development comes as H5N1 bird flu continues to ravage animal populations across the globe and sporadically infect humans. 

Since October alone, more than nine million birds have been culled following farm outbreaks in the US, Canada, and Europe. The virus has also become endemic in US dairy cattle, and was detected in European cows in the Netherlands for the first time last week.

At least 70 people in the US have caught the virus since 2024, mostly after close contact with sickened animals, one of which died.