Moderna says mRNA flu shot has better immune response in study than currently available vaccine

Moderna said Wednesday that its experimental mRNA-based seasonal flu vaccine generated a stronger immune response against four strains of the flu virus than a currently marketed vaccine in a Phase 3 study, paving the way for the company to discuss a path to approval with regulators.

The experimental shot, dubbed mRNA-1010, was compared with a currently approved seasonal flu vaccine from GSK called Fluarix. The results are from an interim analysis and were disclosed in a company news release Wednesday morning.

The announcement doesn't come in time to affect this year's flu season as the vaccine still needs to go through the regulatory approval process.

Moderna is racing Pfizer to bring mRNA technology to seasonal flu vaccines in a bid to improve how well they can target circulating strains. The companies also have plans to combine Covid-19 mRNA shots with those for flu and RSV in the years ahead if studies show that they're safe and effective.

If studies continue to go well, Moderna CEO Stephen Hoge says they could have a combo shot ready by 2025.

Also Wednesday, Moderna said it expects a decision from the US Food and Drug Administration on its mRNA vaccine for RSV in adults 60 and older by April. Pfizer and GSK received FDA approval for their adult RSV vaccines, which use a different technology, in May.

"Our mRNA platform is working," Moderna Chief Executive Officer Stephane Bancel said in the news release. "With today's positive phase 3 flu results, along with previous results in Covid and RSV, we are now three for three on advancing respiratory disease programs to positive phase 3 data."

It hasn't been a straight path to this point for Moderna's flu program; a previous version of the experimental shot generated a strong immune response against A strains of the virus but not against B strains. Moderna reformulated the vaccine, and that led to the latest results.

A major question for mRNA flu shots is their tolerability, given the side effect profile of the shots for Covid, which can cause pain at the injection site, muscle aches, fatigue and other reactions. Moderna said the safety findings were similar in this study to previous ones, which found muscle pain, headache, fatigue, pain and swelling as the most common reactions.

The results focused on the immune response generated by the experimental vaccine rather than how well it protects against disease from flu. Seasonal flu vaccines are generally approved based on the immune response they generate, since that's a faster way to measure their likely effect.

Moderna said Wednesday that a separate phase 3 study didn't generate enough cases to provide efficacy data, and the company decided to stop that study in light of the new Phase 3 data.

The currently available seasonal flu vaccines use older technology than mRNA; the most common approach is to grow either killed or weakened flu virus in chicken eggs, a process that can be more time-consuming.

Just like for the mRNA Covid-19 vaccines, mRNA flu vaccines deliver genetic instructions for the body to make portions of the flu virus, which the immune system then learns to recognize and can fight when it sees the real thing.

The hope is that seasonal mRNA flu vaccines can be designed and manufactured more quickly than shots based on older technology. That's important because the flu virus mutates quickly, and matching the strains as closely to the start of flu season as possible could improve efficacy.

ABC7 contributed to this story.

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