Respiratory Syncytial Virus (RSV): Prevention Strategies and Product Introduction

Maternal Vaccination

Maternal RSV vaccination works by stimulating the production of antibodies to RSV in pregnant women, which are then transferred to their infants through the placenta. The vaccine is administered during the third trimester and infants are protected for up to six months after birth.

Rollout and Uptake

Maternal vaccination was first introduced in 2024. In Argentina, more than half of eligible pregnant women received the vaccine during the 2024 RSV season [14]. Uptake in the United States, however, was suboptimal—only 1 in 3 eligible pregnant women received the vaccine during the 2024–25 RSV season [15].

Of the countries that have introduced the maternal vaccine, most (14, or 64%) utilize a seasonal vaccination schedule, administering the vaccine only during months preceding or overlapping with the local RSV transmission season, while the remaining eight countries (36%) administer the vaccine year-round. The recommended timing of administration varies, though most countries administer between 32–36 weeks (13, or 52%) or 24–36 weeks (8, or 32%).

Impact 

Maternal vaccination is highly effective at protecting infants from severe disease. A retrospective case-control study in Argentina found 78.6% effectiveness (95% CI: 62.1–87.9) against RSV-associated lower respiratory tract disease (LRTD) requiring hospitalization among infants under 3 months and 71.3% (95% CI: 53.3–82.3) among infants under 6 months [16]. These results confirm that the immunization offered by maternal vaccination can protect an infant in the earliest months of life, the period when children are most vulnerable. 

A modeling study estimated that maternal vaccination could avert 2.97 million non-severe RSV cases, 2.63 million severe cases, 2.03 million hospitalizations, and 126,552 deaths among infants under 6 months across 131 LMICs over 10 years [13]. This would equal 17% of severe RSV cases and 25% of RSV-related deaths among infants under 6 months [13].

WHO Prequalification and Recommendations 

The high cost and limited supply of RSV prevention products originally restricted their use to high-income countries. However, in March 2025, the first maternal RSV vaccine was prequalified by WHO, a milestone that will hopefully expand access to children everywhere [17]. 

Following this prequalification, WHO released a position paper in May 2025 outlining recommendations for RSV immunization, including mAbs [18]. Specific recommendations include: 

• All countries should introduce products to prevent severe RSV disease among young infants.
• In countries implementing maternal vaccination, a single dose of RSV vaccine should be administered during the third trimester, ideally at least 2 weeks before delivery to allow sufficient time for antibody transfer.
• In countries introducing mAbs, a single dose should be administered at birth (or at the earliest opportunity) to infants up to 12 months who are entering their first RSV season. 

The recommendations also clarify that an infant whose mother was vaccinated during pregnancy typically should not receive a dose of mAb. Additionally, although a seasonal approach to immunization can be implemented in countries with established seasonal patterns of RSV transmission, it may be more feasible and cost-effective to administer RSV immunization products throughout the year in tropical or subtropical regions where RSV disease occurs throughout the year. 

Next Steps 

Now that RSV vaccination products have been introduced, efforts should focus on ensuring that children everywhere have access to these products and promoting uptake through targeted communication strategies. 

To date, the high cost of these products has been a significant constraint. Following the WHO prequalification, Gavi announced a funding window for establishing an RSV maternal vaccine program and has recently entered the design phase of this new program [19,20]. A multi-dose vial of the maternal RSV vaccine is currently in development, a presentation that would reduce manufacturing and distribution costs. Support from Gavi and other donors will be critical to enable introduction in LMICs, especially as other new vaccines compete for limited funding. RSV mAbs are prohibitively expensive, and there is not yet a funding mechanism available to support their introduction in LMICs. 

As we have seen in the United States, availability of an RSV vaccine does not guarantee its uptake. Pregnant and lactating women who may be hesitant to receive the RSV vaccine have expressed concerns about its safety [21]. Evidence from placebo-controlled trials suggests risks of severe adverse events (such as congenital abnormalities or intrauterine growth restriction) were similar between vaccinated and placebo groups, with the frequency of events being rare in both groups, though monitoring will continue [22]. This highlights the need for focused community sensitization prior to vaccine introduction. These efforts should target both pregnant women as well as health care workers, who are important drivers of vaccine uptake among this population [23].   

Key Takeaways 

• Due to high disease burden and the unavailability of RSV disease-specific treatment, prevention of RSV is critical to reduce morbidity and mortality among infants and children.
• mAbs and maternal vaccination have been demonstrated to be effective at protecting young infants from severe disease and reducing the strain on the health system.
• Although WHO’s prequalification of the maternal RSV vaccine will hopefully expand access to these products in LMICs, sustainable funding will be critical to facilitate their introduction.
• Community sensitization efforts will be key to ensuring high uptake of RSV prevention products once they are more widely available.

Additional Resources

RSV Scenario Modeling Hub

WHO RSV Roadshow

WHO Position Paper