A Vaccine in Pregnancy or an Antibody for the Baby? How Families Can Now Protect Newborns from RSV

What a US trial (Rostad et al., 2026), Australia's national programme (Wadia et al., 2026) and a study of European hospitals (Perramon-Malavez et al., 2026) tell parents about the two ways to protect babies, and about using both

Babies can now be protected from RSV, a common virus that can make very young babies seriously ill, in two ways: a vaccine given to the mother during pregnancy, or a protective antibody injection given to the baby. Three studies from 2026, from the United States, Australia and Europe, show that both options work well, that giving both appears safe, and that reaching families early matters as much as which option is chosen.

Why the first months of life matter so much

Respiratory syncytial virus, usually called RSV, is a common cold virus. In young babies it can cause bronchiolitis, an infection that inflames the smallest breathing tubes and can make feeding and breathing hard. A large worldwide study found that about 45 out of every 100 hospital admissions and hospital deaths from serious RSV chest infections in children under 5 happen in babies younger than 6 months [1]. This is why protecting babies from birth has been a long-standing goal.

How families used to face the RSV season

Until recently, most parents had no way to prevent RSV. An antibody medicine called palivizumab existed, but expert guidance kept it for the small group of babies at greatest risk of severe illness [2]. For most families, RSV season meant relying on everyday precautions and hoping for the best. Two new tools changed that. The first is a vaccine given to the mother late in pregnancy, called RSVpreF. Her body makes protective antibodies, which cross the placenta to the baby before birth. A large study in 18 countries, the Maternal Immunization Study for Safety and Efficacy (MATISSE), found that this vaccine prevented about 8 in 10 serious RSV chest infections in babies during their first 3 months [3], and about 7 in 10 over the first 6 months [4]. The second is nirsevimab, a long-lasting antibody given to the baby as a single injection. In the MELODY trial, which compared nirsevimab with a dummy injection in healthy babies born at or near full term at 160 sites in 21 countries, it prevented about three-quarters of RSV chest infections needing medical care over 5 months [5]. In 2023, US experts recommended either option and said that most babies do not need both [6][7].

That left parents and doctors with new questions. Is it safe to give both? Is one better? And when whole countries pick one approach, does it actually keep babies out of hospital?

Three studies, three different questions

The three studies covered here fit together like steps on a ladder. The first, led by Dr Rostad, was a randomised trial, meaning a computer decided by chance which approach each family received, so the groups could be compared fairly [8]. It took place at 8 US research sites in a network funded by the National Institute of Allergy and Infectious Diseases (NIAID). It included 181 healthy pregnant women, 32 to 36 weeks pregnant, who were put into one of four groups: the vaccine only; the vaccine plus nirsevimab for the baby at birth; the vaccine plus nirsevimab at 3 months; or nirsevimab at birth only. The researchers looked at side effects and measured antibody levels in the babies' blood, but the study did not track how many babies caught RSV, and it was too small to compare how well each approach prevents illness.

The second study, led by Dr Wadia, followed the first year of Australia's national programme offering both products free [9]. From February 2025, pregnant women could have the vaccine any time of year from 28 weeks of pregnancy, and nirsevimab was offered mainly to babies whose mothers had not been vaccinated, or had been vaccinated less than two weeks before birth, and to higher-risk babies. Researchers at 13 hospitals compared 2,719 young children admitted with RSV against 1,024 admitted with similar illnesses who tested negative. If protected babies turn up much less often among those with RSV, the protection is working.

The third study, led by Dr Perramon-Malavez, looked at emergency department visits and hospital admissions for bronchiolitis in several European places in the 2024–2025 winter [10]. Catalonia in Spain was in its second year of giving nirsevimab to babies, Rome in Italy was in its first, and four UK hospitals were in the first year of offering the vaccine in pregnancy. Two hospitals in Iceland and Romania, with no such programme, were included for comparison.

What the researchers found

The trial was reassuring about safety. No serious side effects linked to either product were seen in mothers or babies, including when both were given [8]. After the nirsevimab injection, 17 in 100 babies had soreness or redness where the needle went in, and 60 in 100 had general symptoms such as sleepiness or fussiness. These were mild or moderate; soreness had gone within about a week and the stronger general symptoms had settled by the end of the first week. Babies in every group had high levels of RSV-fighting antibodies at 6 weeks and at 3 months. In babies whose mothers were vaccinated, these levels were highest at birth and dropped a little by 3 months, while a nirsevimab injection raised them further. High antibody levels are encouraging, but scientists have not yet worked out exactly what level is enough to prevent illness, so this trial cannot tell us which approach prevents more infections.

In Australia, both products cut the chance of a baby being admitted with RSV by a large amount [9]. For babies born into the programme, the mother's vaccine lowered the chance by about 82 in 100 (81.5%), and nirsevimab by about 90 in 100 (89.6%). The gap between the two numbers might simply be chance, so the study cannot say that one product is better than the other. Babies given nirsevimab were also more often born early or had health problems, which makes a fair comparison harder. In the study hospitals outside Western Australia and Queensland (two states that had already offered nirsevimab across the whole state in 2024), admissions with RSV in babies under 3 months fell by about 44 in every 100 compared with 2024.

In Europe the picture was more mixed [10]. In Catalonia, where more than 9 in 10 babies received nirsevimab, emergency visits and admissions for bronchiolitis in babies under 6 months fell to less than half their usual level. In Rome, where the programme started late, there was no clear change. At the four UK hospitals, where only about half of mothers had been vaccinated, there were small reductions or none. Numbers also rose or fell at the comparison hospitals in Iceland and Romania, which had no programme at all, a reminder that some winters are simply worse than others. Reassuringly, Catalonia saw no rise in bronchiolitis admissions and only a very small rise in emergency visits among 1-year-olds, the first group of babies protected by its programme, a sign that they were not simply ending up in hospital a winter later instead.

Why the results looked different in different places

At first glance, Europe and Australia seem to disagree, but they were measuring different things. The European study counted all bronchiolitis, whatever virus caused it, in babies up to 6 months, and could not look separately at the first 3 months, when the mother's vaccine should help most [10]. The Australian study counted only babies with confirmed RSV.

Timing and reach also matter. The vaccine works best when given several weeks before birth, because the antibodies need time to cross the placenta; transfer is highest when vaccination happens at least 5 weeks before delivery [11]. In the UK's first year, many women were vaccinated close to their due date [10]. A UK study found that the vaccine prevented 58 in 100 RSV admissions overall, but 72 in 100 when it was given more than two weeks before birth [12]. In Australia, mothers were vaccinated a typical 44 days before birth [9]. In Scotland, the vaccine protected individual babies very well even though only about half of pregnant women had it [13]. So a product can work brilliantly for each baby who gets it while a programme still leaves many babies unprotected.

What this means for you and your baby

For expectant parents, the main message is encouraging: both options protect babies well, and neither has been shown to be clearly better. If you are offered the vaccine in pregnancy, it is worth asking your midwife or doctor about timing, because having it a few weeks before birth gives your baby the most protection. Keep a note of the date you were vaccinated. If your baby arrives within two weeks of your vaccine, or is born early or with a health condition, your baby's team may suggest nirsevimab as well, and this trial suggests that giving both is safe [8]. Mild soreness or sleepiness after the injection is common and usually settles within a week.

What researchers are working on next

Scientists still want to know how long protection lasts and whether babies need help in a second winter. The US trial is following families for a full year [8]. A large French study found fewer RSV hospital stays among babies given nirsevimab than among babies whose mothers had the vaccine [14], while the Australian study could not confirm a difference, so more comparisons are needed. A newer long-acting antibody, clesrovimab, has also been tested in healthy babies [15]. You can read more on In[Neo]Sight about the vaccine in pregnancy, nirsevimab for all babies and clesrovimab.

The bottom line for families

Not long ago, most babies faced RSV season unprotected. Today, a vaccine in pregnancy and an antibody injection for the baby each prevent most RSV hospital stays, and they can safely be used together when needed. The biggest gains come when as many families as possible are offered protection, and when it is given at the right time.

References

  1. Shi T, McAllister DA, O'Brien KL, et al. Global, regional, and national disease burden estimates of acute lower respiratory infections due to respiratory syncytial virus in young children in 2015: a systematic review and modelling study. Lancet. 2017;390(10098):946-958. doi:10.1016/S0140-6736(17)30938-830938-8) ↩
  2. Caserta MT, O'Leary ST, Munoz FM, Ralston SL. Palivizumab Prophylaxis in Infants and Young Children at Increased Risk of Hospitalization for Respiratory Syncytial Virus Infection. Pediatrics. 2023;152(1):e2023061803. doi:10.1542/peds.2023-061803 ↩
  3. 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 ↩
  4. Simões EAF, Pahud BA, Madhi SA, et al. Efficacy, Safety, and Immunogenicity of the MATISSE (Maternal Immunization Study for Safety and Efficacy) Maternal Respiratory Syncytial Virus Prefusion F Protein Vaccine Trial. Obstet Gynecol. 2025;145(2):157-167. doi:10.1097/AOG.0000000000005816 ↩
  5. Hammitt LL, Dagan R, Yuan Y, et al. Nirsevimab for Prevention of RSV in Healthy Late-Preterm and Term Infants. N Engl J Med. 2022;386(9):837-846. doi:10.1056/NEJMoa2110275 ↩
  6. Fleming-Dutra KE, Jones JM, Roper LE, et al. Use of the Pfizer Respiratory Syncytial Virus Vaccine During Pregnancy for the Prevention of Respiratory Syncytial Virus-Associated Lower Respiratory Tract Disease in Infants: Recommendations of the Advisory Committee on Immunization Practices - United States, 2023. MMWR Morb Mortal Wkly Rep. 2023;72(41):1115-1122. doi:10.15585/mmwr.mm7241e1 ↩
  7. Jones JM, Fleming-Dutra KE, Prill MM, et al. Use of Nirsevimab for the Prevention of Respiratory Syncytial Virus Disease Among Infants and Young Children: Recommendations of the Advisory Committee on Immunization Practices - United States, 2023. MMWR Morb Mortal Wkly Rep. 2023;72(34):920-925. doi:10.15585/mmwr.mm7234a4 ↩
  8. Rostad CA, Healy CM, Nayak JL, et al. Maternal RSV Vaccination, Infant Nirsevimab, or Both: Interim Analysis of a Randomized Trial. Pediatrics. 2026;157(6):e2025075223. doi:10.1542/peds.2025-075223 ↩
  9. Wadia U, Richmond PC, Britton PN, et al. Impact and effectiveness of Australia's 2025 hybrid RSV immunisation program: results from the PAEDS-FluCAN Network. Lancet Reg Health West Pac. 2026;73:101938. doi:10.1016/j.lanwpc.2026.101938 ↩
  10. Perramon-Malavez A, Chiaretti A, Coma E, et al. Real-world impact of nirsevimab immunisation and maternal RSV vaccination against respiratory disease on emergency department attendances and admissions: a multinational retrospective analysis. Lancet Reg Health Eur. 2026;63:101597. doi:10.1016/j.lanepe.2026.101597 ↩
  11. Jasset OJ, Lopez Zapana PA, Bahadir Z, et al. Enhanced placental antibody transfer efficiency with longer interval between maternal respiratory syncytial virus vaccination and birth. Am J Obstet Gynecol. 2025;232(6):554.e1-554.e15. doi:10.1016/j.ajog.2024.10.053 ↩
  12. Williams TC, Marlow R, Cunningham S, et al. Bivalent prefusion F vaccination in pregnancy and respiratory syncytial virus hospitalisation in infants in the UK: results of a multicentre, test-negative, case-control study. Lancet Child Adolesc Health. 2025;9(9):655-662. doi:10.1016/S2352-4642(25)00155-500155-5) ↩
  13. McLachlan I, Robertson C, Morrison KE, et al. Effectiveness of the maternal RSVpreF vaccine against severe disease in infants in Scotland, UK: a national, population-based case-control study and cohort analysis. Lancet Infect Dis. 2026;26(4):362-373. doi:10.1016/S1473-3099(25)00624-300624-3) ↩
  14. Jabagi MJ, Bertrand M, Gabet A, Kolla E, Olié V, Zureik M. Nirsevimab vs RSVpreF Vaccine for Respiratory Syncytial Virus-Related Hospitalization in Newborns. JAMA. 2026;335(9):787-798. doi:10.1001/jama.2025.24082 ↩
  15. Zar HJ, Simões EAF, Madhi SA, et al. Clesrovimab for Prevention of RSV Disease in Healthy Infants. N Engl J Med. 2025;393(13):1292-1303. doi:10.1056/NEJMoa2502984 ↩