Why Some Babies Still Die of RSV, and What Nutrition and Follow-Up Visits Could Change

What a 25-year study of babies with RSV at Kilifi County Hospital in Kenya (Mburu and colleagues, Lancet Global Health, 2026) tells families about risk in hospital and in the months after going home

For most babies, RSV, a very common virus, causes a cough and a few difficult days of breathing, but in some parts of the world it still takes babies' lives. A 25-year study from a hospital on the coast of Kenya found that babies who were underweight or born with a heart condition were most at risk, and that some deaths happened in the months after going home. Good nutrition and follow-up visits may matter alongside the new RSV vaccines and antibody injections.

A common virus with very different outcomes around the world

RSV stands for respiratory syncytial virus. It is the leading cause of chest infections in young children worldwide, and in babies it can cause bronchiolitis or pneumonia, infections of the small airways and lungs that make breathing hard [1]. In countries with well-equipped hospitals, babies admitted with RSV almost always recover; the researchers behind this study note that fewer than 1 in 200 such babies die in high-income countries. Elsewhere the picture is very different. Researchers estimated that in 2019 RSV caused about 3.6 million hospital stays and around 101 400 deaths in children under 5 worldwide, and that more than 97 out of every 100 of these deaths happened in low-income and middle-income countries [2].

How doctors came to understand who is most at risk

For many years, most of what doctors knew about serious RSV came from wealthy countries. There, the babies at greatest risk were those born very early, those with long-term lung problems, and those born with a heart defect, known as congenital heart disease [3][4]. That knowledge shaped prevention: an antibody injection called palivizumab, shown in the late 1990s to reduce hospital stays for RSV in high-risk babies [5], came to be targeted at these groups [1]. More recently, a vaccine given to pregnant mothers was tested in 18 countries and shown to protect babies in their first months [6], and a longer-lasting antibody injection for babies has sharply reduced RSV hospital stays where it has been offered to all eligible babies, as in Galicia, Spain [7].

Meanwhile, researchers around the world began collecting information about children who had died of RSV, especially in poorer countries. A worldwide database known as RSV GOLD, short for the RSV Global Online Mortality Database, gathered 358 such deaths from 23 countries and found that in poorer countries those who died were mostly young babies, typically about 5 months old [8]. The same group later found that many babies die at home or in their community, often even younger, without ever reaching hospital [9]. At Kilifi County Hospital in Kenya, doctors and scientists had been tracking RSV since the early 2000s; an earlier report covering 2002 to 2007 found that about 2 in every 100 children admitted with RSV died, and suggested that vaccines would mainly help by preventing illness rather than deaths [10]. Earlier studies had covered only a few years, so no one had been able to follow the same hospital for decades to see whether things were improving, and to look closely at how a baby's nutrition affected the outcome [1].

How the study was done

Kilifi County Hospital sits on the north coast of Kenya and serves a mostly rural community of roughly 300,000 people, according to the study's authors [1]. The area is also home to a long-running project that keeps a register of local families and links it to hospital visits [11]. Since 2001, a research programme run by the Kenya Medical Research Institute (KEMRI) and the Wellcome Trust has tested children admitted with chest infections for RSV.

Maureen Mburu and her colleagues looked back at the records of every baby under one year old admitted with pneumonia and a positive RSV test between January 2001 and July 2025. That came to 2745 babies [1]. They focused on the 2390 babies aged between 4 weeks and 12 months, and looked at newborns separately. Because the research was a look back at records already collected, it could show which features went along with a higher risk, but it could not prove what caused the deaths.

The team compared the babies who died with those who survived, looking at things nurses and doctors measure on arrival: oxygen levels in the blood, weight compared with other babies of the same age (a "weight-for-age score"), and the measurement around the middle of the upper arm. This arm measurement, called mid-upper arm circumference or MUAC, is taken with a simple tape and is a quick way to spot a baby who is seriously undernourished. They also checked for heart conditions, and followed the babies who went home for a full year.

What the researchers found

Most babies got better. Of the 2390 babies, 2332 went home. Sadly, 58 babies died in hospital, about 1 in every 40, and most of these deaths happened in the first week [1].

Three things stood out. Babies born with a heart defect were at much higher risk: of 37 babies with a heart condition, 10 died. Babies with lower oxygen levels on arrival were also more likely to die. And nutrition mattered a great deal. Babies who died were, on average, much lighter for their age than survivors. Among the 54 babies who died and had their arm measured on arrival, 38, about 7 in every 10, had a measurement below 11.5 centimetres, the cut-off for severe malnutrition. Among the babies who survived and were measured, about 3 in every 4 were above that cut-off [1]. This difference showed up in almost every month of age, from 1 to 12 months.

Over the whole 25 years, the share of babies who died did not go down, and the nutrition of babies arriving at the hospital did not improve either [1].

The months after going home

The researchers then followed the 2332 babies who went home. Over the next year, 38 of them died, most within the first 3 months. That means that of the 96 babies aged 4 weeks to 12 months who died, about 4 in every 10 died after leaving hospital [1]. Babies with heart defects or who were badly underweight were most at risk: of babies with a heart defect who went home, about 85 in every 100 were still alive a year later, compared with about 99 in every 100 babies without these problems. A large study of sick children in 9 hospitals in 6 countries across Africa and south Asia, called the Childhood Acute Illness and Nutrition (CHAIN) Network, found something similar for many kinds of illness: almost half of the deaths happened after children had gone home [12].

We cannot be sure that RSV itself caused every death after discharge, because sick babies often have several health problems at once. But the pattern points to a time when extra support could help.

What this means for families

If your baby is in a hospital in a high-income country with RSV, it is important to know that deaths there are rare, and this study does not change that. The findings matter most for babies in places where malnutrition is common and hospitals have fewer resources.

The study suggests a few things that families and care teams everywhere can keep in mind. Weight and growth checks matter: undernutrition is thought to play a part in nearly half of all child deaths worldwide [13], and a study pooling information from 17 countries found that the youngest, most underweight babies face the highest risk of dying [14]. If your baby has a heart condition or has had trouble gaining weight, it is reasonable to ask your care team whether your baby is eligible for RSV protection, and to keep every follow-up appointment after a hospital stay. If your baby seems to be breathing hard, feeding poorly or getting weaker after coming home, it is right to seek care again quickly. You can read more about RSV protection in our articles on the vaccine given in pregnancy and on the antibody injection for babies.

Keeping the findings in perspective

This study came from one hospital in Kenya, so the results may differ elsewhere. Only 58 babies died in hospital, which makes some of the estimates uncertain. Babies who died at home without reaching hospital were not counted, so the true number of RSV deaths in the area is probably higher [1]. The researchers also did not have information on whether each baby was born early or small, which can affect weight.

What researchers are working on next

The authors believe that the new vaccines and antibody injections are a major step forward, but that on their own they may not be enough to prevent RSV deaths in places like Kilifi [1]. They suggest that babies who are undernourished should be seen as high-risk when they have RSV, with closer monitoring, early feeding support and planned check-ups after going home. Future research will need to test whether these steps save lives, and whether the vaccine given in pregnancy protects undernourished babies as well as it protects others.

The bottom line

Over 25 years at one Kenyan hospital, most babies admitted with RSV recovered, but about 1 in 40 died in hospital and more died in the months after going home. Babies with heart defects, low oxygen levels or poor nutrition were most at risk. Alongside new ways of preventing RSV, simple steps such as measuring and supporting a baby's growth and following up after discharge may help more babies survive.

References

  1. Mburu MW, Nyadzua Katama E, Safari MS, et al. In-hospital and post-discharge mortality among infants with respiratory syncytial virus in rural Kenya: a 25-year retrospective cohort study. Lancet Glob Health. 2026;14(9):104003. doi:10.1016/j.langlo.2026.104003 ↩
  2. Li Y, Wang X, Blau DM, et al. Global, regional, and national disease burden estimates of acute lower respiratory infections due to respiratory syncytial virus in children younger than 5 years in 2019: a systematic analysis. Lancet. 2022;399(10340):2047-2064. doi:10.1016/S0140-6736(22)00478-000478-0) ↩
  3. Chaw PS, Wong SWL, Cunningham S, Campbell H, Mikolajczyk R, Nair H. Acute Lower Respiratory Infections Associated With Respiratory Syncytial Virus in Children With Underlying Congenital Heart Disease: Systematic Review and Meta-analysis. J Infect Dis. 2020;222(Suppl 7):S613-S619. doi:10.1093/infdis/jiz150 ↩
  4. Deng S, Cong B, Edgoose M, De Wit F, Nair H, Li Y. Risk factors for respiratory syncytial virus-associated acute lower respiratory infection in children under 5 years: An updated systematic review and meta-analysis. Int J Infect Dis. 2024;146:107125. doi:10.1016/j.ijid.2024.107125 ↩
  5. The IMpact-RSV Study Group. Palivizumab, a Humanized Respiratory Syncytial Virus Monoclonal Antibody, Reduces Hospitalization From Respiratory Syncytial Virus Infection in High-risk Infants. Pediatrics. 1998;102(3):531-537. doi:10.1542/peds.102.3.531 ↩
  6. Kampmann B, Madhi SA, Munjal I, et al. Bivalent Prefusion F Vaccine in Pregnancy to Prevent RSV Illness in Infants. N Engl J Med. 2023;388(16):1451-1464. doi:10.1056/NEJMoa2216480 ↩
  7. Ares-Gómez S, Mallah N, Santiago-Pérez MI, et al. Effectiveness and impact of universal prophylaxis with nirsevimab in infants against hospitalisation for respiratory syncytial virus in Galicia, Spain: initial results of a population-based longitudinal study. Lancet Infect Dis. 2024;24(8):817-828. doi:10.1016/S1473-3099(24)00215-900215-9) ↩
  8. Scheltema NM, Gentile A, Lucion F, et al. Global respiratory syncytial virus-associated mortality in young children (RSV GOLD): a retrospective case series. Lancet Glob Health. 2017;5(10):e984-e991. doi:10.1016/S2214-109X(17)30344-330344-3) ↩
  9. Mazur NI, Löwensteyn YN, Willemsen JE, et al. Global Respiratory Syncytial Virus-Related Infant Community Deaths. Clin Infect Dis. 2021;73(Suppl_3):S229-S237. doi:10.1093/cid/ciab528 ↩
  10. Nokes DJ, Ngama M, Bett A, et al. Incidence and severity of respiratory syncytial virus pneumonia in rural Kenyan children identified through hospital surveillance. Clin Infect Dis. 2009;49(9):1341-1349. doi:10.1086/606055 ↩
  11. Scott JA, Bauni E, Moisi JC, et al. Profile: The Kilifi Health and Demographic Surveillance System (KHDSS). Int J Epidemiol. 2012;41(3):650-657. doi:10.1093/ije/dys062 ↩
  12. Childhood Acute Illness and Nutrition (CHAIN) Network. Childhood mortality during and after acute illness in Africa and south Asia: a prospective cohort study. Lancet Glob Health. 2022;10(5):e673-e684. doi:10.1016/S2214-109X(22)00118-800118-8) ↩
  13. Black RE, Victora CG, Walker SP, et al. Maternal and child undernutrition and overweight in low-income and middle-income countries. Lancet. 2013;382(9890):427-451. doi:10.1016/S0140-6736(13)60937-X60937-X) ↩
  14. WHO Risk Stratification Working Group (WHO-RSWG). Infant-level and child-level predictors of mortality in low-resource settings: the WHO Child Mortality Risk Stratification Multi-Country Pooled Cohort. Lancet Glob Health. 2025;13(5):e843-e858. doi:10.1016/S2214-109X(25)00045-200045-2) ↩