It was roughly a year after the earliest cases of covid-19 before the first vaccines against the SARS-CoV-2 virus were ready for roll-out. By then millions had died worldwide and economies were devastated. In the advent of a bird flu pandemic, we will be able to react more rapidly, because we should have an mRNA vaccine already approved and ready to go. A phase III trial of such a vaccine is now getting under way 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 at the UK Health Security Agency.

The main threat is a strain of H5N1 bird flu called clade 2.3.4.4b. It has spread globally in wild birds since evolving around a decade ago, even reaching the Antarctic. Many wild mammals have been infected by wild birds and it has often spread to poultry farms. In the US, it has been circulating in dairy cattle.

There have been more than 100 human cases since 2024, although so far there is no evidence of the virus spreading from person to person. But as long as H5N1 bird flu keeps circulating, the risk will remain.

“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 at Moderna.

The company’s mRNA-1018 vaccine against H5N1 bird flu has already undergone phase I and II trials, with no safety concerns found. Now a phase III trial that will involve 3000 volunteers in the UK and 1000 in the US is starting.

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Normally trials measure the effectiveness of vaccines directly, but since H5N1 bird flu isn’t spreading among people, the trial will instead look at the strength of the immune response in the volunteers. The results of the earlier trials suggest the vaccine evokes a strong response, says Hiruy.

The trial is prioritising people aged over 65 and people who work with poultry, as they are most at risk from bird flu.

Some countries do already have stockpiles of conventional vaccines against H5N1 bird flu. For instance, . But this existing vaccine is made using chicken eggs, like many vaccines against the seasonal flus circulating in people. With this technique, it is very difficult to rapidly scale up production or make changes to the vaccine if viruses evolve significantly.

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By contrast, mRNA vaccine production can be rapidly scaled up and it’s very easy to change the vaccine should that prove necessary. So mRNA vaccines have major advantages when it comes to pandemic preparation, says Pebody.

The trial is (CEPI), which is backed by more than 30 countries and other organisations. CEPI stepped in after the US government cut funding for mRNA vaccines.

Countries such as and the US may also roll out H5N1 vaccines for farm animals, especially poultry. This approach has long been used in some other countries, with a study in France finding that vaccinating ducks dramatically reduced H5N1 outbreaks on farms.

A person in Louisiana has died from a bird flu virus known as H5N1. This is the first known death related to the virus in the US. The Louisiana Department of Health (LDH) has not identified additional H5N1 cases in the state nor found evidence of person-to-person transmission, indicating that the risk to the general public remains low.

The person was hospitalised for the virus in December, after contracting it from infected or dead birds in their backyard. They experienced severe respiratory symptoms. It was the first serious case of H5N1 in the US. The LDH announced their death on and said that they were older than 65 and had underlying health conditions.

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In total, 66 people in the US have tested positive for H5N1, according to the (CDC). Most of them developed mild symptoms, such as eye redness, and worked with infected cows or chickens.

H5N1, which has killed tens of millions of wild and domestic birds worldwide, has been circulating in dairy cows across the US for almost a year now. of samples collected from the person in Louisiana indicate that the person was infected with the D1.1 genotype of the virus, which is similar to the viruses recently detected in wild birds, but distinct from the version spreading in cattle. There is no evidence that the virus can transmit between people.

The analysis also identified several changes that may improve the virus’ ability to bind to cells in the upper airways of humans, which largely lack receptors for most bird flu viruses. According to the CDC, it is likely these changes happened after the person was infected – any time someone contracts a bird flu virus, it gives it a chance to evolve and become better at spreading between us. One of the changes was also seen in a person who fell severely ill with H5N1 in Canada in November.

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