Maternal RSV vaccine candidate effective but upped risk for preterm birth
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Key takeaways:
- Preterm birth incidence was higher in the vaccine group in a recent trial.
- GSK told Healio that they have discontinued the vaccine’s trials.
A GSK respiratory syncytial virus vaccine candidate was effective but trials saw a higher incidence in preterm birth, according to research published in the New England Journal of Medicine.
Last summer, the FDA approved Pfizer’s Abrysvo, which is meant to prevent RSV in infants during their first 6 months after birth when given to pregnant patients in the second or third trimester. Just before Abrysvo’s approval, the FDA also approved nirsevimab, a monoclonal antibody to prevent RSV in infants entering their first RSV season and the first approved formulation to protect against medically attended RSV in newborns and infants.
Researchers at GSK, which had its adult RSV vaccine Arexvy approved by the FDA last year in a historic first, examined a vaccine candidate for maternal protection in a phase III trial on an RSV prefusion F protein-based maternal vaccine.
A total 5,328 pregnant women aged 18 to 49 took part in the study across 24 countries. A treatment group of 3,557 women received the vaccine and a control group of 1,771 received the placebo. Researchers then followed 3,426 infants born of the vaccine group and 1,711 in the control group up to 6 months of age.
In the months following the infants’ births, 16 infants in the vaccine group and 24 control infants had any type of medically assessed RSV-associated disease, with a vaccine efficacy of 65.5% (95% credible interval, 37.5 to 82). The authors did find, however, that preterm birth occurred in 6.8% of the infants in the vaccine group and in 4.9% in the control group.
The results suggest that the “risks of any and severe medically assessed RSV-associated lower respiratory tract disease among infants were lower with the candidate maternal RSV vaccine than with placebo but that the risk of preterm birth was higher with the candidate vaccine,” as per the study.
In a statement and responses to questions submitted by email, a GSK spokesperson told Healio that they “do not have a mechanistic explanation for the preterm birth safety signal.”
The spokesperson said that GSK has “discontinued [their] work on this RSV maternal candidate vaccine,” and are closing out all ongoing trials except for an MAT-015 follow-on study to monitor subsequent pregnancies.
“Patient safety remains our utmost priority, and we continue to work with study investigators to ensure the best care possible for the women and children involved,” the GSK spokesperson said. “A follow-on study to monitor subsequent pregnancies of women that participated in any of the RSV maternal candidate vaccine clinical studies (RSV MAT-015) is ongoing. We have continually kept regulatory authorities and study investigators updated since we stopped enrollment and vaccination in our RSV maternal trials.”
The study was accompanied by an editorial, with authors Sonja A. Rasmussen, MD, of the Johns Hopkins University School of Medicine, and Denise J. Jamieson, MD, MPH, of the University of Iowa Carver College of Medicine, noting that in light of the imbalance in the incidence of preterm birth in the phase 3 trial, “postmarketing surveillance of the bivalent vaccine is warranted.”
“Even if there is a true association between the receipt of the bivalent vaccine and preterm birth, it is essential to weigh this small risk against the proven benefits of maternal RSV vaccination,” the authors wrote. “Moreover, any potential risk of preterm birth associated with the receipt of the bivalent vaccine is reduced by the administration of the vaccine at 32 weeks or more of gestation.”
References:
Dieussaert I, et al. N Engl J Med. 2024;doi:10.1056/NEJMoa2305478.
Rasmussen SA, et al. N Engl J Med. 2024;doi:10.1056/NEJMe2401072.
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