Recent advancements in unlocking access to RSV prevention for children in LMICs

97% of RSV-related paediatric deaths occur in LMICs

Respiratory syncytial virus (RSV) remains a major cause of illness and death among infants and young children worldwide. Each year, RSV-associated acute lower-respiratory tract infections (ALRI) lead to around 3.6 million hospitalisations and an estimated 101,400 deaths in children under five – making it the second leading cause of under-five mortality after malaria.¹ More than 97% of these deaths occur in low- and middle-income countries (LMICs), where infants and young children remain particularly vulnerable.

With no treatment options available, maternal and paediatric vaccines or monoclonal antibodies (mAbs) (hereinafter referred to as ‘RSV preventive medicines’) offer a clear path to reducing the RSV burden in LMICs. Maternal vaccines, administered during pregnancy, help protect infants from RSV in their first months of life through the transfer of maternal antibodies, while mAbs and paediatric vaccines offer immunity via direct administration to infants.

Until recently, however, no RSV preventive medicines suitable for widespread use had been developed to address this need. Since 2023, three RSV preventive medicines have been approved by the US Food and Drug Administration (FDA): Pfizer’s RSV vaccine (Abrysvo^®) and AstraZeneca/Sanofi’s mAb nirsevimab (Beyfortus^®),^* both of which have also secured regulatory approval in multiple LMICs. Most recently, on 9 June 2025, Merck & Co. (MSD)^** received US FDA approval for its mAb clesrovimab (Enflonsia). In recognition of the threat RSV poses to public health, the World Health Organization (WHO) launched the Global RSV Surveillance Programme in 2016, followed by the development of Preferred Product Characteristics for RSV vaccines in 2017 and mAbs in 2021, to help guide the development of RSV preventive medicine suitable for use in LMICs. 

Wider access to maternal and paediatric RSV preventive medicines can reduce morbidity and mortality, while also easing pressure on health systems and lowering economic costs for households (see Figure 1). A study showed that, over a nine-year period across 131 LMICs, maternal vaccines could prevent an estimated 2.6 million severe RSV cases in infants, while mAbs could prevent an additional 7.1 million.² In response to this pressing need, several pharmaceutical companies have taken steps to address the RSV burden by developing new maternal and paediatric preventive medicines.

Recent company developments in RSV preventive medicines

Growing pipeline, but clinical trials need to include more LMICs

Industry-led clinical trials for RSV vaccines and mAbs have increased in recent years – especially over the last five years (see Figure 2).^*** Five companies are leading the development (clinical Phase II/III and Phase III) of RSV preventive medicines, four of which – AstraZeneca, MSD, Pfizer and Sanofi – are included in the 2024 Access to Medicine Index (the 2024 Index).^† 

Phase II/III and Phase III clinical trials by these four companies were run in at least one LMIC listed in the 2024 Index in the last five years for the products shown in Figure 3. Sanofi's intranasal paediatric vaccine candidate, SP0125, currently in Phase III of development, shows particular promise for use in LMICs due to its mode of administration. Its intranasal delivery may support rollout in resource-limited settings, as it is less invasive and involves simpler training for healthcare workers. Sanofi recently expanded one trial to the Dominican Republic, bringing the total number of LMICs involved to ten.

However, people living in LMICs continue to face a disproportionate disease burden. Companies can include more LMICs in these clinical trials, as they remain underrepresented compared to high-income countries. Phase II/III and Phase III clinical trials for RSV preventive medicines targeting children in the last five years were run in 12% of the 113 LMICs included in the 2024 Index. Most trials have been concentrated in upper-middle-income countries, particularly Mexico and South Africa. Among the five countries with the highest incidence of RSV-related ALRI in children under five, only South Africa has been included.^‡ Gambia remains the sole low-income country where such trials are held. 

Conducting clinical trials in LMICs is important, as companies often prioritise access planning in countries where trials are conducted – a key step towards achieving broad and equitable access.³ These trials can give patients early access to promising new medicines and vaccines while also improving understanding of how different populations respond to them.

Abrysvo^®’s WHO prequalification clears path for Gavi inclusion

The WHO prequalified Pfizer’s maternal vaccine on 12 March 2025, following recommendations from the Strategic Advisory Group of Experts (SAGE) (see Figure 3). This made Pfizer’s RSV vaccine (Abrysvo^®) the first RSV preventive medicine targeting children to receive WHO prequalification (WHO PQ) – a key milestone that can serve as a catalyst for better access. The WHO PQ is a prerequisite for procurement by United Nations agencies such as UNICEF or by Gavi, the Vaccine Alliance (Gavi), and it can also accelerate registration in LMICs through the WHO Collaborative Registration Procedure.

Shortly after, on 13 March 2025, Gavi welcomed the WHO decision and confirmed that a new RSV vaccine investment case would be re-presented to its Board in 2025. This follows Gavi’s initial in-principal approval from 2018, which was conditional on the absence of a licensed, WHO-prequalified and SAGE-recommended product. With all prerequisites now met, Pfizer’s RSV vaccine (Abrysvo^®) is expected to be considered for inclusion in Gavi’s portfolio – a move that could expand access to maternal vaccination for the prevention of RSV in children across the 54 LMICs currently eligible within Gavi’s portfolio.⁴ In the same statement, Gavi stated that a multi-dose vial of Pfizer's RSV vaccine (Abrysvo^®) is being developed with the support of the Gates Foundation. If successful, this presentation could improve affordability by reducing manufacturing and distribution costs and help catalyse the delivery of the maternal vaccine in lower-income countries.

However, ongoing uncertainties in global health funding – such as those affecting Gavi – emphasise the need for companies with RSV preventive medicines that have already been approved, or are nearing approval, to continue their efforts and explore additional opportunities to expand access in LMICs. This is particularly important for countries outside Gavi’s current scope, many with a high RSV incidence.^‡

New regulatory approvals and partnerships in LMICs

The US FDA’s 9 June 2025 approval of MSD’s mAb, clesrovimab (Enflonsia), marks another milestone in RSV prevention. The decision can pave the way for future regulatory approvals in LMICs, including the LMICs where clinical trials are conducted.⁵ This, in turn, could help expand protection for infants during their first RSV season (see Figure 3). In anticipation, the Medicines Patent Pool (MPP) had already moved clesrovimab (Enflonsia) from its watchlist to its priority list in the March 2025 Prioritisation of Medicines for In-Licensing report. The priority list identifies medicines for which voluntary licensing could deliver substantial public health benefits. Securing a non-exclusive voluntary licence through MPP could strengthen the pathway for future access to RSV preventive medicines in LMICs.

With this latest approval, the number of RSV preventive medicines authorised by the US FDA since 2023 has grown to three, as efforts to register in LMICs gain momentum. Pfizer's RSV vaccine (Abrysvo^®) is registered in 12 LMICs (as of 31 May 2024),^§,3 while Sanofi^* has secured regulatory approval in five LMICs for nirsevimab (Beyfortus^®).^6-8 

Following this, Sanofi has established a distribution partnership with Dr. Reddy’s in India (see Figure 3), an LMIC with one of the highest numbers of RSV-related ALRI cases in children under the age of five.^‡ Dr. Reddy’s extensive local network in India can help ensure AstraZeneca/Sanofi’s medicine reaches children in need. Additionally, Sanofi, in collaboration with AstraZeneca, has recently announced efforts to accelerate global distribution of nirsevimab (Beyfortus^®). The company also reported expanded production capacity and additional manufacturing sites since the product’s launch in 2023. While specific recipient countries were not named, these steps suggest potential benefit for children in LMICs.

Pathways to further expand access

While recent momentum around access to RSV preventive medicines is encouraging, companies still have opportunities to build on this progress. Several viable pathways remain open for companies to further expand access and increase their impact (see Figure 1). These recommendations align with and expand on existing ones identified for MSD, Pfizer and Sanofi in the 2024 Access to Medicine Index.

Companies can pursue supranational procurement through partners such as UNICEF and Gavi – a model that has proven successful in other childhood immunisation programmes. For example, Pfizer has supplied its pneumococcal vaccine via Gavi and is estimated to have helped protect over 300 million children over 15 years in countries with the greatest need. A similar pathway could be followed for RSV preventive medicines. UNICEF’s upcoming RSV-focused tender, scheduled for the first quarter of 2026, provides a window for engagement.

Another way to improve access and availability is through engaging in non-exclusive voluntary licensing agreements either before, or soon after regulatory approval. Such agreements will be vital for LMICs outside of Gavi’s portfolio, as these countries will not be covered by the same financial support. Voluntary licensing has already proven successful for medicines used to treat other viral infections, such as HIV and hepatitis C. To accelerate access to RSV mAbs, the MPP has already included two mAbs – MSD's clesrovimab (Enflonsia) and AstraZeneca/Sanofi’s nirsevimab (Beyfortus^®) – on its priority list. These could become the first mAbs to be licensed via MPP.

Given that most companies commit to registering in countries where they have conducted trials, expanding the breadth of clinical trials to include more LMICs – particularly for maternal and paediatric immunisation – would be an important step. Additionally, companies can further improve availability by registering and subsequently supplying their medicines in more LMICs. Expanding clinical trials and registrations is especially important in countries with the highest RSV-related disease incidence in children under five, such as Eswatini, Botswana, South Africa, Lesotho and Namibia.^‡ 

While these are examples of actions companies can take, other stakeholders also play a role in expanding access to RSV preventive medicines. Following WHO’s SAGE recommendation on 30 May 2025, which supports the use of approved RSV preventive medicines to reduce the global burden of severe RSV disease in infants, countries are encouraged to consider their introduction through national immunisation programmes.⁹ Such efforts are essential to catalyse company action and help address some of the challenges manufacturers face. 

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_{*AstraZeneca and Sanofi established an agreement to develop and commercialise nirsevimab (Beyfortus^®). AstraZeneca leads development and manufacturing activities, and Sanofi leads commercialisation activities in all countries, including LMICs, and records revenue. The two companies share costs and profits in all territories except the US. (https://www.astrazeneca.com/media-centre/press-releases/2023/beyfortus-approved-in-the-us-for-the-prevention-of-rsv-lower-respiratory-tract-disease-in-infants.html)}

_{**Throughout this analysis, Merck & Co. is abbreviated to MSD.} 

_{***The analyses in the section ‘Growing pipeline, but clinical trials need to include more LMICs’ were based on two sources: PATH (https://www.path.org/) and ClinicalTrials.gov (https://clinicaltrials.gov/). RSV clinical trials published until 31 January 2025 were included.}   

_{†GSK also invested in developing a maternal RSV preventive medicine, with a candidate that advanced to Phase III clinical trials but is no longer in development (https://www.gsk.com/en-gb/media/press-releases/gsk-provides-update-on-phase-iii-rsv-maternal-vaccine-candidate-programme/).} 

_{‡The incidence and number of ALRI cases in children under five data has been obtained from reference 1. The Lancet study included 137 countries, covering all 113 countries in scope of the 2024 Access to Medicine Index, with the exception of Kosovo, Marshall Islands, Moldova, Palestine, Saint Lucia, State of/West Bank Gaza, Tuvalu and Ukraine.} 

_{§The term ‘registration’ includes both countries where the medicine has been approved or filed for registration. The number of countries where Pfizer’s RSV vaccine (Abrysvo^®) is registered was obtained from the 2024 Access to Medicine Index.} 

References

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6. Sanofi. Press Release India Sanofi receives marketing authorization for Beyfortus^® in India to protect infants & children against Respiratory Syncytial Virus (RSV). Published online August 31, 2024. https://www.sanofi.com/assets/countries/india/docs/Media/press-releases/2024/sanofi-receives-marketing-authorization-for-beyfortus-in-india-to-protect-infants-and-children-against-respiratory-syncytial-virus-rsv.pdf 

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