Which way protects babies best from RSV: a birth shot or a vaccine for mom?
A shot given to the baby at birth offers the more reliable protection. In this study of 164,140 infants, babies who got nirsevimab shortly after birth had about a 22 percent lower odds of being hospitalised for an RSV lung infection than babies protected only by their mother’s vaccine (odds ratio 0.78, 95% confidence interval 0.70 to 0.86). But timing changed the picture in an important way.
RSV stands for respiratory syncytial virus. It is a common bug that causes coughs and colds in most people. In babies, though, it can settle deep in the lungs and make breathing hard. RSV is one of the top reasons young infants end up in the hospital during their first winter. So protecting newborns from it matters a great deal.
There are now two ways to do this. The first is nirsevimab, a long-acting antibody shot given straight to the baby soon after birth. The second is RSVpreF, a vaccine given to the mother during pregnancy, between 28 and 36 weeks of gestation, so she passes protection to her baby before birth. Until now, it was not clear which approach worked better in the real world.
What the data show
This was a French nationwide retrospective cohort study, not a randomised trial. It used national health records to follow 164,140 infants born between September 2024 and February 2025, covering the 2024 to 2025 RSV season. Researchers compared the two strategies head to head by looking at who ended up in the hospital with an RSV-related lower respiratory tract infection, meaning an infection in the lungs and airways, by age 6 months. To make the comparison fair, they matched 42,098 babies from each group on birth date, region, and sex, then adjusted for other baseline differences.
Over the 6 months of follow-up, 753 babies were hospitalised for an RSV lung infection: 350 of 42,098 in the nirsevimab group (0.83 percent) and 403 of 42,098 in the maternal vaccine group (0.96 percent). After adjustment, nirsevimab was associated with 22 percent lower odds of RSV hospitalisation. But the most useful finding was about timing. When mothers were vaccinated 8 weeks or more before giving birth, the difference between the two strategies was no longer statistically detectable (odds ratio 1.01, 95% confidence interval 0.77 to 1.32). The advantage for nirsevimab showed up when the maternal vaccine was given closer to delivery: 2 to under 4 weeks before (0.45, 0.32 to 0.63), 4 to under 6 weeks (0.80, 0.68 to 0.95), and 6 to under 8 weeks (0.80, 0.60 to 0.99).
Dr. Kumar’s Take
This is real-world data from an entire country’s health records, not a controlled lab result. More than 164,000 babies is a large enough number to show how these two tools actually perform in everyday practice, and the absolute hospitalisation rates in both groups were under 1 percent, which is worth holding onto.
My honest read is that nirsevimab at birth is the more forgiving option, because it does not depend on getting the timing right during pregnancy. It protects the baby directly and right away. That said, I would not call the maternal vaccine second best. It is simply more sensitive to timing. When mothers were vaccinated at least 8 weeks before delivery, their babies did about as well as babies who got the antibody shot. The vulnerability is the pregnancy that ends sooner than expected, or the vaccine given late. So the lesson is less “one is better” and more “timing is the lever you can actually control.”
The timing analyses in this study were secondary and exploratory, so I hold them a little more loosely than the main result. But they point in a direction that fits how maternal antibody transfer is understood to work.
Who benefits most
The clearest winners from early action are babies born during or just before RSV season, when the virus is spreading. A newborn’s lungs and immune system are still developing, so they have the least defence against a serious lung infection. For families who choose the maternal vaccine route, getting it done well ahead of the due date is what carries the protection across to the baby.
This is also reassuring for parents who, for any reason, miss the maternal vaccine window. Nirsevimab given at birth offers a strong fallback that does not rely on what happened earlier in pregnancy. Either path can protect a baby. The key is making sure one of them is in place before RSV season arrives.
Limitations to keep in mind
This was a retrospective cohort study, which means researchers looked back at records of what already happened rather than randomly assigning babies to each strategy. That design is powerful for size and real-world relevance, but it cannot prove cause and effect as cleanly as a randomised trial. Families who chose one option may differ in other ways from families who chose the other, and while the researchers matched and adjusted for what they could measure, they could not adjust for what the records do not capture. Babies who received neither product were left out entirely, so this compares the two strategies against each other, not against nothing.
The findings also reflect one country and one RSV season. Virus activity, healthcare access, and which product is offered can all vary from place to place and year to year.
Practical Takeaways
- If you are pregnant and plan to use the maternal RSV vaccine, aim to get it at least 8 weeks before your due date, since that was the interval at which babies did about as well as those given nirsevimab at birth.
- If the vaccine timing window is missed or your baby arrives early, ask your doctor about giving nirsevimab to your baby shortly after birth as a direct form of protection.
- Talk with your obstetrician or paediatrician about which RSV strategy fits your pregnancy timeline, since both were associated with low hospitalisation rates in this study.
- Plan ahead so protection is in place before RSV season, which usually runs through the colder months.
Related Studies and Research
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FAQs
Is nirsevimab a vaccine or something different?
Nirsevimab is not a traditional vaccine. It is a long-acting antibody, which means it gives the baby ready-made protection rather than training the baby’s own immune system to make it. That is why it can be given to the baby at birth. A vaccine, like the RSVpreF given to mothers, prompts the body to build its own defences over time, which is why the interval between the shot and delivery mattered so much in this study.
Can a baby get both the maternal vaccine and nirsevimab?
This study compared the two approaches against each other rather than testing them in combination, so it cannot answer that question. In my practice I treat this as a decision to make with your paediatrician, who can weigh when in pregnancy the mother was vaccinated, when the baby was born, and the baby’s individual risk.
Why does the 8-week timing before delivery matter so much?
After a mother gets the RSVpreF vaccine, her body needs time to make protective antibodies and pass them across the placenta to the baby. In this study, babies whose mothers were vaccinated 8 weeks or more before delivery had hospitalisation odds that were not statistically different from babies given nirsevimab at birth.
Bottom Line
In a large real-world study of 164,140 infants in France, giving nirsevimab to babies at birth was associated with about 22 percent lower odds of RSV-related lung infection hospitalisation by age 6 months compared with the mother’s vaccine alone. But that difference disappeared when mothers were vaccinated 8 weeks or more before delivery. The takeaway is practical and hopeful: both tools were linked to low hospitalisation rates, and timing is the factor families and doctors can plan around.
