Three RSV vaccines are currently approved in the United States: GSK’s Arexvy, Pfizer’s Abrysvo, and Moderna’s mResvia. All three are designed for adults, and one of them, Abrysvo, is also approved for use during pregnancy to protect newborns. Each uses a slightly different technology, but they share the same goal: preventing the severe lower respiratory tract infections that RSV causes in older adults and very young infants.
The Three Approved RSV Vaccines
All three vaccines target the same part of the virus, a protein on RSV’s surface called the prefusion F protein. This is the form the virus uses to enter your cells, and training the immune system to recognize it produces a strong protective response.
Arexvy (GSK) and Abrysvo (Pfizer) are both protein-based vaccines. They deliver a lab-made version of that prefusion F protein directly, prompting your immune system to build antibodies against it. mResvia (Moderna) takes a different approach, using mRNA technology similar to the platform behind Moderna’s COVID-19 vaccine. Instead of delivering the protein itself, it delivers genetic instructions that tell your cells to temporarily produce the protein, triggering an immune response.
In clinical trials, the mRNA vaccine showed 83.7% efficacy against RSV-associated lower respiratory tract disease and 68.4% efficacy against RSV-related acute respiratory illness in adults 60 and older. All three vaccines are given as a single dose.
Who Should Get an RSV Vaccine
The CDC recommends RSV vaccination for all adults 75 and older, period. For adults between 50 and 74, the vaccine is recommended if you’re at increased risk for severe RSV illness. Risk factors include chronic lung disease, chronic heart disease, a weakened immune system, living in a nursing home or long-term care facility, and other conditions that make respiratory infections more dangerous.
If you’re in the 50 to 74 range and think you qualify, you don’t need to bring medical records to prove it. The CDC has made clear that your own statement about having a risk factor is sufficient, and vaccinators should not turn you away for lack of documentation. Your healthcare provider can also use their clinical judgment and local RSV trends to recommend the vaccine more broadly within that age group.
How the Maternal Vaccine Protects Newborns
Pfizer’s Abrysvo is the only RSV vaccine approved for use during pregnancy. When given between 32 and 36 weeks of gestation, it prompts the mother’s immune system to produce antibodies that cross the placenta and protect the baby after birth. The recommended window for vaccination is September through January, timed to cover the RSV season.
The protection for infants is substantial. In the phase 3 clinical trial, maternal vaccination reduced a baby’s risk of being hospitalized for RSV by 68% in the first three months of life and by 57% through six months. For the most severe outcomes, including dangerously low oxygen levels, the need for mechanical ventilation, or ICU admission, the vaccine reduced risk by 82% in the first three months and 69% through six months.
RSV Antibodies for Infants Are Not Vaccines
For babies whose mothers didn’t receive the RSV vaccine during pregnancy, or whose vaccination status is unknown, there’s another option: monoclonal antibody products like nirsevimab and clesrovimab. These are not vaccines. They don’t activate the baby’s immune system or teach it to fight RSV. Instead, they deliver ready-made antibodies that provide immediate, temporary protection.
An RSV antibody product is recommended for infants under 8 months who are entering their first RSV season if the mother wasn’t vaccinated, if her vaccination status is unknown, or if the baby was born within 14 days of the mother receiving the vaccine (not enough time for adequate antibody transfer). Most infants whose mothers were vaccinated at least 14 days before delivery won’t need the antibody product. For certain high-risk children between 8 and 19 months, nirsevimab is also recommended heading into their second RSV season.
None of the three adult RSV vaccines are approved for infants or children.
Side Effects and Safety Concerns
The most common side effects of RSV vaccines are the ones you’d expect from any vaccination: pain at the injection site, fatigue, headache, and muscle aches. These are generally mild and resolve within a few days.
The more notable safety signal involves Guillain-Barré syndrome, a rare neurological condition in which the immune system attacks the nerves. The FDA now requires a GBS warning on the prescribing information for both Arexvy and Abrysvo. Post-approval data from insurance claims suggest an increased risk of GBS in the 42 days following vaccination, with an estimated 9 excess cases per million doses of Abrysvo and 7 excess cases per million doses of Arexvy in people 65 and older. During clinical trials, GBS cases were extremely rare: one case of GBS and one case of a related condition (Miller-Fisher syndrome) among roughly 22,000 people who received Abrysvo, and one case among roughly 16,000 people who received Arexvy.
To put that in perspective, the baseline rate of GBS in the general population is roughly 1 to 2 cases per 100,000 people per year. The additional risk from RSV vaccination is real but very small, and for most people in the recommended age groups, the risk of severe RSV disease is considerably higher.
When to Get Vaccinated
RSV circulates most heavily from fall through spring in the United States, with peak activity typically in winter. Vaccination ahead of the season gives your immune system time to build protection before the virus is widespread. For pregnant women, the specific September-through-January window aligns vaccination timing with the months when a newborn is most likely to encounter RSV.
Current recommendations call for a single dose rather than annual boosters. Data on how long protection lasts beyond one or two seasons is still being collected, so guidelines on revaccination may evolve as more information becomes available.