Maternal RSV Vaccine: How Long Does Protection Last for Mother and Baby?

Medically reviewed by Dr. Salman Ahmad Bajwa, MBBS — Last updated: July 2026

Respiratory syncytial virus (RSV) remains one of the leading causes of severe lower respiratory tract illness in infants worldwide. Since the approval of the first maternal RSV vaccine (Pfizer’s Abrysvo, RSVpreF), pregnant women now have a way to pass protective antibodies to their babies before birth. Here’s what the latest clinical and real-world data show.

Quick Answer

The maternal RSV vaccine (Abrysvo), given at 32–36 weeks of pregnancy, protects a newborn for approximately 6 months after birth, with the strongest protection (up to 82% efficacy) in the first 90 days of life. Protection is best when the vaccine is given at least 2–5 weeks before delivery — doses given in the final two weeks provide little to no benefit.

How Maternal Vaccination Protects the Baby

When a pregnant woman receives the RSV vaccine, her immune system produces antibodies against the RSV prefusion F protein. These antibodies cross the placenta via active transport, a process that becomes clinically significant around 28 weeks of gestation and, by 36 weeks or later, results in the baby often having higher antibody levels than the mother herself. This is the same biological principle behind maternal vaccination programs for tetanus, pertussis, and influenza.

Clinical Trial Results (MATISSE Phase 3)

The pivotal MATISSE trial enrolled more than 7,300 pregnant participants across 18 countries, vaccinated between 24–36 weeks of gestation. Results showed:

• 81.8% efficacy against severe RSV-related lower respiratory illness within the first 90 days of the infant’s life
• 69.4% efficacy through 180 days
• Approximately 57% efficacy against any medically attended RSV illness through 180 days
• When vaccination was restricted to the officially approved 32–36 week window, efficacy against severe disease reached roughly 76.5% at 180 days

Safety data from the trial were reassuring overall, with similar adverse event rates between vaccine and placebo groups. A small, statistically non-significant increase in preterm births was observed in the vaccinated group, which is why regulatory approval was limited to the 32–36 week gestational window rather than the broader trial range.

What Real-World Data Now Shows

Since rollout, population-level studies have started confirming — and in some cases exceeding — the original trial numbers:

• Scotland’s national vaccination program found vaccine effectiveness of about 83% against RSV-related hospitalization in infants under 90 days old, with even higher effectiveness (around 89%) observed in preterm infants specifically.
• UK-based research found effectiveness of about 72% against hospitalization when the vaccine was given more than two weeks before delivery.
• Argentine multicenter studies independently found effectiveness in the high 70% range against hospitalization in infants under three months.

One especially important real-world finding: vaccination given less than two weeks before delivery showed little to no protective benefit, reinforcing that timing relative to delivery is just as important as timing relative to RSV season.

How Long Does Protection Actually Last?

Maternal antibodies protect a baby for roughly six months after birth, though the level of protection gradually declines over that period — every dataset shows meaningfully stronger effectiveness at 90 days than at 180 days. Because of this waning effect combined with seasonal administration timing, health authorities generally recommend vaccination timed so the six-month protection window aligns with the local RSV season, rather than vaccinating far in advance of it.

For subsequent pregnancies, current guidance does not recommend repeat maternal doses. Instead, infants from later pregnancies are typically offered a long-acting monoclonal antibody (such as nirsevimab) directly after birth.

Does the Vaccine Protect the Mother Too?

This is a less studied side of the equation. RSV can cause meaningful illness in adults, and there is biological plausibility that vaccination reduces maternal illness severity, but the major clinical trials were primarily designed and powered to measure infant outcomes, not maternal ones. Direct evidence of maternal-side clinical benefit is still comparatively thin and worth watching as more data emerges.

Key Takeaways

• Protection is transferred from mother to baby via the placenta and is strongest when there are at least two-to-five weeks between vaccination and delivery.
• Peak protection occurs in the first 90 days of life, gradually declining through 6 months.
• Real-world effectiveness data from multiple countries is now aligning with, and in some cases exceeding, clinical trial results.
• Timing the vaccine relative to both gestational age and the local RSV season matters for maximizing infant protection.

Frequently Asked Questions

How long does the maternal RSV vaccine protect a newborn?
Approximately 6 months, with the strongest protection in the first 90 days after birth.

When is the best time to get the RSV vaccine during pregnancy?
Between 32 and 36 weeks of gestation, ideally at least 2–5 weeks before delivery. Vaccination in the final two weeks before birth has not shown meaningful protective benefit.

Does the RSV vaccine protect the mother, or only the baby?
The vaccine is primarily studied and approved for infant protection through antibody transfer. Evidence of direct protective benefit for the mother herself is limited and still being researched.

Can I get the RSV vaccine in every pregnancy?
Current guidance does not recommend repeat doses in subsequent pregnancies. Babies from later pregnancies are typically offered a long-acting RSV antibody (nirsevimab) shortly after birth instead.

Is the maternal RSV vaccine safe?
Large clinical trials found similar rates of adverse events between vaccinated and placebo groups. A small, statistically non-significant increase in preterm birth was observed, which is why the approved dosing window is restricted to 32–36 weeks.

How effective is the RSV vaccine in real-world use, not just clinical trials?
Real-world studies from Scotland, the UK, and Argentina have found effectiveness ranging from about 72% to 89% against RSV-related infant hospitalization, generally consistent with or better than clinical trial results.

References

1. Efficacy of the maternal RSVpreF (Abrysvo) vaccine in preventing RSV-related hospitalization in infants. Droracle. https://www.droracle.ai/articles/1191624/what-is-the-efficacy-of-the-maternal-rsvpref-abrysvo
2. Regulatory review of benefits and risks of preventing infant RSV disease through maternal immunization. NCBI. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11528063/
3. Maternal RSV vaccination to protect infants: current evidence and future directions. Exploration Publications. https://www.explorationpub.com/Journals/eaa/Article/100988
4. ABRYSVO® Efficacy Data. Pfizer. https://abrysvomaternal.pfizerpro.com/about-abrysvo/efficacy
5. Maternal RSV Vaccine and Nirsevimab Effectiveness against Medically Attended RSV Disease in Infants, United States. NCBI. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12793056/
6. Effectiveness of Maternal RSV Vaccination in Conferring Infant Immunity. MDPI. https://www.mdpi.com/2076-393X/14/3/232
7. Effectiveness of RSV Immunization among Infants in Their First RSV Season, US. NCBI. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12792840/
8. Effectiveness of ABRYSVO® Maternal RSV Vaccine Against RSV in Infants in Western Pennsylvania. ClinicalTrials.gov. https://clinicaltrials.gov/study/NCT06813872
9. Vaccine effectiveness of the maternal RSVpre-F vaccine against severe disease in infants in Scotland, UK. medRxiv. https://www.medrxiv.org/content/10.1101/2025.08.01.25332515.full.pdf
10. RSV Vaccine Guidance for Pregnant Women. CDC. https://www.cdc.gov/rsv/hcp/vaccine-clinical-guidance/pregnant-people.html
11. A Study to Determine the Safety and Efficacy of the RSV F Vaccine to Protect Infants Via Maternal Immunization. ClinicalTrials.gov. https://cdn.clinicaltrials.gov/large-docs/47/NCT02624947/Prot_000.pdf
12. Clinical Presentation and Birth Outcomes Associated with RSV Infection in Pregnancy. NCBI. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4816499/
13. Immunizations to Protect Infants. CDC. https://www.cdc.gov/rsv/vaccines/protect-infants.html
14. Pregnancy and RSV. Family Doctor. https://familydoctor.org/pregnancy-and-rsv/
15. RSV Vaccine: A Breakthrough in Protecting Infants and Expectant Mothers. NETEC. https://netec.org/2024/12/20/rsv-vaccine-a-breakthrough-in-protecting-infants-and-expectant-mothers/
16. Why I Recommend the RSV Vaccine to My Pregnant Patients. ACOG. https://www.acog.org/womens-health/experts-and-stories/the-latest/why-i-recommend-the-rsv-vaccine-to-my-pregnant-patients

This article draws on clinical trial data (MATISSE) and real-world effectiveness studies from Scotland, the UK, Argentina, and the United States.

admin