If a bird flu pandemic starts, we may have an mRNA vaccine ready

About a year following the first covid-19 cases, vaccines against the SARS-CoV-2 virus became available. By that time, millions had died globally, and economies were in turmoil. Should a bird flu pandemic occur, our response could be swifter, thanks to a pre-approved mRNA vaccine. A phase III trial for such a vaccine is now beginning in the UK and the US.

“A flu pandemic is the most likely future pandemic. And it’s really critical that we ensure we’re properly prepared,” says Richard Pebody at the UK Health Security Agency.

The primary concern is a variant of H5N1 bird flu known as clade 2.3.4.4b. Over the past decade, it has spread worldwide in wild birds, even reaching the Antarctic. Numerous wild mammals have contracted it from birds, and it has frequently been transmitted to poultry farms. In the US, it has been found in dairy cattle.

Since 2024, there have been over 100 human cases, yet there is no evidence of human-to-human transmission. However, as long as H5N1 circulates, the threat persists.

“We cannot predict the timing or the severity of the next pandemic. However, with continued circulation of influenza viruses in animal populations, and the potential for virus adaptation, preparedness remains essential,” says Hiwot Hiruy at Moderna.

Moderna’s mRNA-1018 vaccine for H5N1 bird flu has passed through phase I and II trials without any safety issues. Now, a phase III trial involving 3000 volunteers in the UK and 1000 in the US is commencing.

While vaccine trials typically evaluate direct effectiveness, the absence of H5N1 spread among humans means this trial will focus on measuring the immune response in participants. Previous trials indicate the vaccine elicits a strong immune reaction, according to Hiruy.

The trial prioritizes individuals over 65 and those working with poultry, as they face the highest risk from bird flu.

Some nations already have reserves of conventional H5N1 bird flu vaccines. For example, the UK has 5 million doses. However, these vaccines, produced using chicken eggs like many seasonal flu vaccines, are challenging to rapidly scale up or modify if the virus undergoes significant changes.

In contrast, mRNA vaccines offer rapid scalability and can be easily adjusted if necessary, providing significant advantages for pandemic preparedness, according to Pebody.

The trial is funded by the Coalition for Epidemic Preparedness Innovations (CEPI), supported by over 30 countries and other organizations. CEPI stepped in after the US government reduced funding for mRNA vaccines.

Nations like the UK and the US might also consider H5N1 vaccines for farm animals, particularly poultry. This practice has been used in other countries, with a French study showing significant reductions in H5N1 outbreaks on farms after duck vaccination.