RSV vaccines

Following RSV Pre-F vaccination during pregnancy, recipients may experience injection site pain, which is mild to moderate. Systemic symptoms, including muscle pain and headaches may also occur.^{Go to footnote 11}

In clinical trials, serious adverse events included a numerical increase in preterm births in maternal vaccine recipients (this was not statistically significant overall, and available data are insufficient to establish or exclude a causal relationship between preterm birth and the vaccine).^{Go to footnote 22} 

A numerical imbalance in preterm births (< 37 weeks gestation) was observed between the groups, occurring in 5.7% of vaccine recipients and 4.7% of placebo recipients (relative-risk [RR]: 1.20; 95% CI: 0.98–1.46).

When the data were stratified by country income levels, the numerical increase in pre-term births was most notable in the two upper-middle-income countries (UMICs), namely Argentina and South Africa.^{Go to footnote 33}

The safety of RSV pre-F vaccine, specifically the risk of excess pre-term births is being further evaluated in the ongoing RSV_IMPACT study in sub-Saharan African settings.^{Go to footnote 44}

Post-authorization safety evaluations in high-income countries and UMICs that have introduced the vaccine have not shown any risk of excess pre-term infants.^{Go to footnote 55}

Unpublished post-marketing data presented to the Global Advisory Committee on Vaccine Safety (GACVS) in June 2026 did not show any excess pre-term births following maternal Pre-F vaccine use in Australia, Argentina, Brazil and the United Kingdom.^{Go to footnote 66}

In a modelling study looking at risk-benefit in South Africa, maternal vaccination was estimated to prevent 31 RSV-associated infant deaths per 100 000 live births, but if the increase in preterm births occurred at the same rate observed in the trial, the model predicted that neonatal deaths related to prematurity could increase by 44 per 100 000 births when vaccination occurred between 24–36 weeks of gestation. However, if vaccination was limited to 27–36 weeks gestation, the predicted risks were substantially lower, and in 97% of simulations the benefits outweighed the risks. Overall, the findings suggest that third-trimester RSV Pre-F vaccination may provide a more favourable benefit-risk balance.^{Go to footnote 77}

Since the risk of pre-term births was mainly observed at two upper-middle-income country sites and data were very sparse from low- and low-middle-income countries, a trial that is powered to detect the risk of excess pre-term births has been initiated in four sub-Saharan African countries (the IMPACT study).^{Go to footnote 44}

In postmarketing safety surveillance in Spain, the common adverse events reported following the administration of nirsevimab included maculo-papular and papular rash, and injection site pain, induration, oedema and swelling. The rate of serious adverse events was 23.1/ 100 000 doses administered. No antibody-dependent enhancement or other unexpected risks were reported.^{Go to footnote 88}

In healthy pre-term and term infants, serious adverse events were reported in 278 of 2 409 infants (11.5%) in the clesrovimab group and 149 of 1 202 infants (12.4%) in the placebo group.^{Go to footnote 99} In children at high risk for severe RSV disease entering their second RSV season, a 210 mg dose of clesrovimab was well tolerated.^{Go to footnote 1010}