Is the RSV Vaccine an mRNA Vaccine?

Most approved RSV vaccines are not mRNA vaccines. Of the three RSV vaccines that have reached the market globally, two are protein subunit vaccines and only one uses mRNA technology.¹ The confusion is understandable: mRNA vaccines became household names during the COVID-19 pandemic, and hearing “new respiratory virus vaccine” can trigger the assumption that the same technology is involved. But RSV vaccine development followed its own long, complicated path, and the platform behind each product matters for how it works, how it’s stored, and how much it costs.

Three Approved Vaccines, Two Different Technologies

The three RSV vaccines approved for use in older adults are Arexvy (made by GSK), Abrysvo (made by Pfizer), and mResvia (made by Moderna). Arexvy and Abrysvo are both protein subunit vaccines, meaning they deliver a lab-manufactured piece of the RSV virus directly into your body to train your immune system. mResvia is the only one that uses mRNA, the same basic platform behind the Pfizer-BioNTech and Moderna COVID-19 shots.²

The difference between these platforms is practical, not just academic. With a protein subunit vaccine, the manufacturer grows the target protein in a laboratory, purifies it, and packages it into a vial. Your immune system encounters a finished protein when you get the shot. With an mRNA vaccine, the vial contains genetic instructions wrapped in a lipid nanoparticle. After injection, your own cells read those instructions and temporarily produce the target protein themselves, which the immune system then recognizes and responds to. The end goal is the same: teach the immune system what RSV looks like so it can fight the real virus later. The route to that goal is different.

Despite using different platforms, all three approved vaccines zero in on the same viral target: the RSV fusion protein, locked into its prefusion shape. Decades of research established that this prefusion form of the F protein is the most effective antigen for triggering strong, virus-neutralizing antibodies.³ The protein changes shape dramatically when RSV fuses with a human cell, and the prefusion version exposes surfaces that the immune system responds to most powerfully. Stabilizing this protein so it doesn’t flip into its post-fusion form before the immune system gets a good look at it was one of the biggest engineering challenges in RSV vaccine development.⁴

Why RSV Vaccines Took So Long

RSV was identified as a major cause of respiratory illness decades ago, yet vaccines didn’t arrive until 2023. The reason traces back to a genuine tragedy. In 1967, infants and toddlers who received a formalin-inactivated RSV vaccine got sicker, not better, when they later encountered the actual virus. Hospitalizations spiked, and two vaccinated toddlers died.⁵ The formalin treatment had destroyed the prefusion shape of the F protein, leaving behind a version that triggered antibodies unable to actually neutralize the virus.⁶ Worse, the immune response skewed toward a pattern that caused damaging inflammation in the lungs upon real infection.

That disaster effectively froze RSV vaccine research for decades. Scientists had to figure out exactly what went wrong before anyone would risk trying again. Later work showed that the formalin inactivation process stripped away the prefusion form of the F protein entirely, leaving only the post-fusion form on the vaccine’s surface.⁷ The breakthrough came when researchers mapped the atomic structure of the prefusion F protein and figured out how to stabilize it artificially. That structural work, which took years of computational and experimental effort, is the foundation all three current vaccines rest on.⁸ Without it, none of them would exist, regardless of whether the final product uses a protein or mRNA.

How Well Each Vaccine Performs

The three vaccines have been tested in large trials, though comparing them head-to-head is tricky because each trial used slightly different definitions of illness and enrolled different populations. That said, the broad numbers give a sense of what each one does.

Moderna’s mRNA vaccine, mResvia, showed strong protection in older adults. In its pivotal trial, it was roughly 84% effective at preventing RSV-associated lower respiratory tract disease with at least two symptoms, and about 68% effective against RSV-related acute respiratory illness more broadly. Protection held up against both RSV subtypes, A and B, and was consistent across age groups and people with underlying health conditions.⁹

GSK’s Arexvy, a protein subunit vaccine with an adjuvant (a booster ingredient that strengthens the immune response), demonstrated about 67% efficacy against RSV-associated lower respiratory tract disease over two RSV seasons on a single dose. Against severe disease, efficacy was higher, around 79%. Researchers also tested whether a booster shot after one year added benefit. It didn’t: the revaccination regimen was well tolerated but didn’t meaningfully improve protection beyond the first dose.¹⁰

Pfizer’s Abrysvo, the other protein subunit vaccine (which contains prefusion F proteins from both RSV subtypes A and B but no adjuvant), showed about a 58% reduction in RSV-associated illness in older adults, with immune responses lasting at least 12 months.¹¹ Abrysvo is also the only RSV vaccine approved for use in pregnant people, where the goal is to pass protective antibodies to the baby before birth.

The durability of protection is an open question for all three vaccines. Neutralizing antibody levels decline over time, though they tend to stay above pre-vaccination levels for at least a year.¹⁰ How often people will need revaccination, if at all, is still being studied.

Protecting Infants Is a Different Problem

You can’t give any of the three approved RSV vaccines directly to a baby. Infants are the age group most vulnerable to severe RSV, but their immature immune systems don’t respond to these vaccines the way an adult’s does, and the 1960s disaster looms large over any attempt to vaccinate very young children directly. Instead, two distinct strategies exist for infant protection, and neither one is an mRNA vaccine.

The first is maternal vaccination with Abrysvo. Pregnant people receive the shot during the third trimester, and the antibodies they produce cross the placenta and protect the newborn during the first months of life. The second approach skips vaccination entirely: nirsevimab is a monoclonal antibody given directly to the infant. Rather than teaching the baby’s immune system to make its own antibodies, nirsevimab provides ready-made antibodies that work immediately.

Recent real-world data from large population studies have compared these two approaches directly. In a national cohort study, infants who received nirsevimab at birth had about a 22% lower chance of being hospitalized for RSV-related lower respiratory tract infection compared to infants whose mothers received Abrysvo during pregnancy.¹² Another study found even larger differences for severe outcomes: nirsevimab was associated with roughly 40% lower risk of needing ICU admission or ventilator support compared to maternal vaccination.¹³ These findings are reshaping how pediatricians and public health agencies think about the best strategy for protecting newborns.

The Guillain-Barré Signal

Post-marketing surveillance has flagged a potential link between RSV vaccination and Guillain-Barré syndrome (GBS), a rare autoimmune condition in which the immune system attacks the peripheral nervous system. This signal has emerged for the protein subunit vaccines used in older adults, not specifically for the mRNA vaccine.

A study of England’s older adult vaccination program estimated that the bivalent protein subunit vaccine (Abrysvo) was associated with about 23 excess GBS cases per million doses. The researchers found the risk to be real but small, and concluded it was far outweighed by the vaccine’s benefits in preventing severe RSV disease.¹⁴ An analysis of U.S. Medicare beneficiaries found elevated GBS incidence after both protein subunit vaccines, with estimated excess cases of fewer than 10 per million doses for each product. The FDA has maintained that the overall benefits of RSV vaccination outweigh this identified risk.¹⁵ Ongoing monitoring continues across all approved RSV vaccines.¹⁶

To put those numbers in perspective: GBS is already a rare condition, occurring in the general population at a background rate of roughly 1 to 2 cases per 100,000 people per year from all causes. The additional risk from RSV vaccination, while detectable, doesn’t change the overall calculus for most older adults at risk of severe RSV.

Who Should Get Vaccinated and When

In 2023, the CDC’s Advisory Committee on Immunization Practices recommended that adults aged 60 and older may receive a single dose of RSV vaccine, using shared clinical decision-making between the patient and their healthcare provider. The recommendation specifically calls for vaccination before the start of RSV season, though typical seasonal patterns were disrupted by the COVID-19 pandemic and haven’t fully settled back into their pre-pandemic rhythm.¹⁷

“Shared clinical decision-making” is a significant distinction from a universal recommendation. It means the vaccine isn’t automatically suggested for every person over 60 the way flu shots are. Instead, the decision should factor in your age, your health conditions, whether you’ve already been vaccinated, and your personal risk tolerance. People with chronic lung disease, heart disease, or weakened immune systems stand to benefit most.

A practical question many people have is whether you can get an RSV vaccine at the same appointment as your flu shot or COVID booster. The answer is yes. Studies in adults 50 and older found that giving an RSV vaccine alongside an influenza or COVID-19 vaccine produced immune responses that were just as strong as giving them separately.¹⁸ That makes it easier to get everything done in a single visit during the fall vaccination season.

The Cost Question Between Platforms

The choice between an mRNA and a protein subunit RSV vaccine isn’t just about biology. Cost-effectiveness analyses show meaningful differences between the two platforms, largely driven by how long protection lasts. A modeling study of older adults aged 75 and up found that protein subunit vaccines with three years of effectiveness cost roughly $46,000 per quality-adjusted life-year gained, a figure generally considered cost-effective by U.S. standards. The mRNA vaccine, assuming only two years of effectiveness, came in at about $101,000 per quality-adjusted life-year. If the mRNA vaccine’s protection also lasted three years, that number dropped to about $71,000.¹⁹

These numbers aren’t something most individuals will negotiate directly, since insurance coverage shapes what you actually pay out of pocket. But they influence which vaccines health systems stock and promote, and they explain why durability of protection is such a closely watched metric. If future data show that the mRNA vaccine protects for three full seasons rather than two, its economic profile improves substantially. If it turns out that any of these vaccines need annual boosters, the cost math changes for all of them.

Why the mRNA Label Creates Confusion

The rollout of RSV vaccines has bumped into a public understanding problem. Many people associate all new respiratory virus vaccines with mRNA technology, either positively or negatively, based on their experience with COVID-19 vaccines. Social media analysis of conversations around RSV prevention in Italy found recurring confusion about the distinction between different RSV prevention options, including maternal vaccines, infant monoclonal antibodies, and adult vaccines, with frequent questions about eligibility, access, and safety.²⁰

For people specifically seeking or avoiding mRNA technology, the distinction matters. If you want an RSV vaccine but prefer not to receive mRNA, Arexvy and Abrysvo are both protein subunit options. If you specifically want the mRNA platform, mResvia is currently the only approved choice. Your doctor should be able to tell you which product their pharmacy or clinic carries, since not every location stocks all three.

The broader RSV vaccine pipeline extends well beyond these three products. Researchers are developing live-attenuated vaccines, recombinant vector-based candidates, and additional mRNA and protein-based formulations targeting different RSV proteins or populations.² The field is still young. The first RSV vaccines only reached the market in 2023 after more than half a century of failed attempts, and the current options are likely the beginning of a longer evolution rather than the final word.