Mike: Pregnant women are sometimes given vaccines to help protect the health of their babies after birth, with Cochrane reviews examining the evidence on this for, for example, pneumococcal disease and hepatitis B. In May 2024, we published a new addition, looking at RSV vaccination. In this podcast, review authors, Emily Phijffer and Odette de Bruin, medical doctors and PhD students in respectively, Pediatrics and Obstetrics at the Wilhelmina Childrens Hospital, University Medical Centre Utrecht in the Netherlands, talk about their findings.

Odette: Hello Emily, first of all, could you say a little about RSV. What is it and what does it do?

Emily: Hello Odette. RSV is short for respiratory syncytial virus, which is a common cause of lower respiratory tract infections in infants. Every year, there are 3.6 million hospital admissions for infants with severe RSV disease and many deaths worldwide. Infants under 6 months old are particularly vulnerable to severe RSV disease because their immune system is not fully developed. Therefore, we aimed to look at whether RSV vaccination for women during pregnancy might help their babies and I’ll pass back to you to tell more about this maternal vaccination. For example, what are the principles and why was it important to do this review?

Odette: During pregnancy, the placenta transports antibodies from the mother's bloodstream to the foetus. Maternal vaccination aims to boost antibody levels in mothers so that more antibodies are transferred to the foetus, providing something called passive immunity. Maternal RSV vaccines have been developing rapidly, and so we wanted to further investigate whether maternal RSV vaccination is an effective way of preventing RSV hospitalisation in infants. Would you like to say what we found?

Emily: There are six studies in nearly 18,000 women in the review, and these provide high quality evidence to support the efficacy of maternal RSV vaccination. It halved the number of RSV-related hospitalisations in infants during their first year of life, such that these fell to 11 per 1000 among vaccinated pregnant women, compared to 22 per 1000 among those who were not vaccinated.

Odette: To achieve this reduction, when in their pregnancy were the mothers vaccinated?

Emily: All six included studies administered the vaccine between 24 and 36 weeks into the pregnancy.

Odette: We also looked at several safety outcomes. These included adverse outcomes during the pregnancy, including intra-uterine growth restriction, stillbirth and maternal death. And, adverse infant outcomes including preterm birth, congenital abnormalities and infant death. However, despite the large number of pregnant women in the studies in the review, there was insufficient evidence to draw firm conclusions on some of these safety outcomes.

Emily: That’s right, but we are confident that maternal RSV vaccination does not increase the risk of congenital abnormalities. And there are probably no safety concerns relating to intra-uterine growth restriction, stillbirth, maternal and infant death. For preterm birth, there might be a higher risk, but we need more research to give an evidence-based result.

Odette: Finishing with our overall take-home message about maternal RSV vaccination: RSV vaccination during pregnancy is effective in preventing infant hospitalisations, lowering the risk by 50%. And despite the limitations with the current evidence, maternal RSV vaccination is considered to be safe. This means that we are in an exciting time where the first shots of maternal RSV vaccines are administered to pregnant women.

Emily: Thanks Odette. If people would like to read the review, how can they get hold of it?

Odette: Thanks Emily. It’s available online. If listeners go to Cochrane Library dot com and type “maternal RSV vaccination” in the search box, they will see our review near the top of the list.