New mRNA flu vaccine far more effective than existing jabs, but has some limitations, study finds

A newly developed mRNA-based flu vaccine is almost 35 per cent more effective against the most common form of influenza, according to a new study.

The phase three trial, whose results were published this morning in the New England Journal of Medicine, involved more than 18,000 people aged between 18 and 64.

Half of the participants were given a standard flu vaccine, while the other half received the new mRNA option developed by Pfizer.

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The study found that the latter was 34.5 per cent more effective at protecting people against influenza A.

"The mRNA vaccine performed better than conventional flu vaccines," Professor Archa Fox from the University of Western Australia, who wasn't involved in the study, said. 

"Only 0.63 per cent of people injected with the mRNA flu vaccine came down with the flu, compared to 0.95 per cent of people injected with the conventional flu vaccine."

The results are similar to a trial of another mRNA flu vaccine developed by Moderna, which showed a 26.6 per cent effectiveness increase compared to a standard vaccine.

However, there weren't enough cases of influenza B in today's study to determine the Pfizer vaccine's effectiveness against that type of virus, and the mRNA jab was also linked to a higher rate of mild to moderate side effects.

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"Lab tests suggested that the new vaccine may not be as effective against B strains," Associate Professor Seth Cheetham from the University of Queensland said. 

"The mRNA vaccine was safe, but an elevated rate of side effects, such as headache and injection site pain, was detected compared to traditional vaccines."

The level of severe side effects, though, was similarly low for both vaccines.

However, the phase three trial showed another limitation of the Pfizer vaccine: a lack of benefit for vulnerable elderly patients.

"Most crucially, it showed no significant benefit for adults over 65, the group most at risk from severe flu, highlighting that this is a promising step forward but not a complete solution for all," molecular virologist Vinod Balasubramaniam said.

Vaccination rates against flu have dropped significantly in recent years in Australia, despite a surge in the number of cases of the potentially deadly illness.

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Experts are hoping the development of mRNA vaccines, using similar technology to what was behind the successful COVID-19 vaccines, could lead to better protection against the virus.

"Manufacturing mRNA vaccines is significantly faster than traditional methods, which rely on growing the virus in eggs or cells, a process that can take six months or more," Dr Emma Grant from La Trobe University said. 

"Faster production means vaccine strains can be selected closer to the flu season, reducing the risk of mismatch with circulating viruses.

"Moreover, as demonstrated with COVID-19 vaccines, mRNA technology can activate multiple arms of the immune system, including long-lived killer T cells that recognise multiple different influenza strains… 

"This capability moves us closer to the long-sought goal of a 'universal' influenza vaccine, one that provides broader and longer-lasting protection."

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