US approval adds complementary option to protein-based vaccines for respiratory syncytial virus

Moderna’s mResvia vaccine has been approved to protect adults aged 60 and older from lower respiratory tract disease caused by respiratory syncytial virus (RSV) infection. The approval was granted under a breakthrough therapy designation and marks the first approved mRNA vaccine for a disease other than Covid-19.

Laboratory scientist working on Moderna RSV vaccine

Source: © Adam Glanzman/Bloomberg/Getty Images

Moderna’s mRNA vaccine joins GSK and Pfizer’s protein-based products for use in over-60s. The firm is also running trials in pregnant women and young children

RSV is a common, seasonal virus that usually causes mild, cold-like symptoms. However, it can be extremely serious in adults over 60 and infants. Two RSV vaccines were approved for older adults across the EU, US and UK in mid-2023 – GSK’s Arexvy and Pfizer’s Abrysvo. Both are recombinant protein vaccines containing stabilised forms of the pre-fusion conformation of the F-protein from both RSV-A and RSV-B virus sub-types. Moderna’s vaccine consists of an mRNA sequence which encodes a stabilised pre-fusion F-protein, which is then expressed in cells to trigger an immune reaction.

The FDA’s approval of mResvia is based on results from a phase 3 trial conducted in around 37,000 adults aged 60 or older in 22 countries. The vaccine efficacy against RSV lower respiratory tract disease was reported as 83.7%, and no serious safety concerns were identified.

‘mResvia protects older adults from the severe outcomes of RSV infection, and it is the only RSV vaccine available in a pre-filled syringe designed to maximise ease of administration, saving vaccinators’ time and reducing the risk of administrative errors,’ said Stéphane Bancel, Moderna’s chief executive, in a statement on 31 May.

Scott Roberts, an expert in infectious diseases at Yale School of Medicine, US, described the approval as significant. ‘It’s never going to be a bad thing to have more vaccine options available to us,’ he says. ‘I’m dealing a lot with vaccine hesitancy in a number of different groups and so having options is really valuable.

‘The significance here is that we have another vaccine mechanism that differs from the GSK and the Pfizer – those are inactivated protein subunit vaccines, and this is a totally separate mechanism,’ he says. ’RSV really impacts the extremes of age, and it leads to deaths on the order of influenza,’ he points out. ‘The reason people don’t think about RSV is that until now, we’ve had nothing [we could] do about it.’

Roberts also highlights the possible – and as-yet unconfirmed – link between adults who received the Pfizer and GSK vaccines and conditions such as atrial fibrillation, Guillain-Barre Syndrome and other neurological conditions; ‘if anybody has a history of those conditions, the obvious answer would be to switch to the mRNA vaccine, which, based on my read of the trial was really well tolerated,’ he says.

Roberts says that he believes mRNA vaccines are now some of the most studied vaccines of all time. ‘I hope that people come away from the Covid-19 vaccines thinking, “wow, these mRNA vaccines worked. They were safe, they were well studied”. And that it’s really easy to get a new vaccine for whatever updated strain is circulating that year.’ However, he acknowledges that this isn’t the universal view. ‘You’re going to have people who say, “I’m never getting an mRNA vaccine”. And I don’t think that’s going to change with the RSV vaccine,’ he adds.

Moderna says it expects to have mResvia available for eligible populations in the US by the 2024–2025 respiratory virus season, which begins around September. It has also filed for approval with regulators in multiple other markets around the world.

The company is also running global phase 2 clinical trials of the vaccine in children and pregnant women, to evaluate its safety and immune response. The eventual aim is to prevent RSV in newborn babies by vaccinating their mothers during pregnancy. Pfizer’s Abrysvo is already approved for vaccinating pregnant women, but GSK’s Arexvy is not, owing to some safety concerns uncovered in clinical trials.