The RSV vaccine provides meaningful protection for at least two to three RSV seasons after a single dose, though its effectiveness gradually declines over time. How long it lasts depends on which vaccine you’re asking about and who received it, since RSV vaccines work differently for older adults, pregnant people, and infants.
Protection for Older Adults
Two RSV vaccines are available for older adults: Arexvy (GSK) and Abrysvo (Pfizer). Both are given as a single injection, not annually. The CDC currently recommends one dose for all adults 75 and older, and for adults 50 to 74 who are at increased risk of severe RSV illness. If you’ve already received one dose, you’re considered fully vaccinated and should not get another dose right now.
The strongest protection comes in the first RSV season after vaccination. Pfizer’s Abrysvo showed 84.4% efficacy against RSV-related lower respiratory tract illness across the first full season and into a partial second season. Protection against cases severe enough to require medical attention was about 81%.
GSK’s Arexvy has the longest follow-up data available. A large phase 3 trial tracked roughly 25,000 participants over three full RSV seasons, with a median follow-up of about 30 months. A single dose maintained 62.9% efficacy against RSV-related lower respiratory tract disease across all three seasons. It worked against both major RSV subtypes: 69.8% efficacy against RSV-A and 58.6% against RSV-B. That’s a noticeable decline from the first-season numbers, but still substantial protection nearly three years out.
One surprising finding from that trial: getting a second dose one year after the first didn’t improve efficacy compared to a single dose. The booster offered protection “within the same range” as one shot alone, which is part of why no booster is currently recommended.
Why Protection Fades
RSV vaccines work by training your immune system to produce antibodies against a key protein on the virus’s surface. Those antibody levels are highest in the weeks after vaccination and gradually decrease over the following months and years. This is normal for most vaccines, and it’s why efficacy drops from roughly 80% in the first season to around 63% by the third.
The CDC and its advisory committee are actively monitoring whether adults will eventually need a second dose. No timeline has been set, but recommendations will be updated as more long-term data comes in. For now, one dose is the complete regimen.
Protection for Infants
RSV protection for babies comes through two different routes, and the duration differs for each.
When a pregnant person receives Abrysvo during weeks 32 through 36 of pregnancy, their body produces antibodies that cross the placenta and protect the newborn. This protection lasts approximately six months after birth, which covers the window when infants are most vulnerable to severe RSV. After that, the borrowed antibodies naturally break down and the protection fades.
The other option is nirsevimab, a monoclonal antibody given directly to the infant by injection. Clinical trials evaluated its effectiveness through 150 days (about five months) after the shot. In most cases, babies only need one or the other. The CDC notes that infants born 14 or more days after their mother received the RSV vaccine generally don’t need nirsevimab as well.
How RSV Vaccines Compare to Annual Flu Shots
Unlike the flu vaccine, the RSV vaccine is not designed as a yearly shot. The flu vaccine changes each year because influenza mutates rapidly, requiring updated formulations. RSV is more genetically stable, which is why a single dose can maintain protection across multiple seasons. That said, the gradual decline in efficacy means the question of whether a booster will eventually be needed remains open. The current evidence supports protection for at least three seasons from one dose, and researchers are continuing to track participants beyond that window.
Who Might See Shorter Protection
People with weakened immune systems, whether from medications, chronic illness, or aging, generally produce fewer antibodies in response to any vaccine. The RSV vaccine trials did not publish separate durability data for immunocompromised adults, so it’s unclear exactly how much shorter their protection might be. This group falls under the “increased risk” category that qualifies for vaccination starting at age 50, but no adjusted dosing schedule exists for them yet. The same single-dose recommendation applies regardless of immune status.