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Maternal Vaccine To Protect Infants Against RSV From Birth Approved by FDA

A person wearing gloves drawing a vaccine up from a vial into a syringe.
Credit: Mufid Majnun/Unsplash
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The US Food and Drug Administration (FDA) has approved the first vaccine against respiratory syncytial virus (RSV), designed for use during pregnancy to protect infants from severe RSV-associated respiratory disease in their first six months of life.

Preventing severe RSV

RSV is an incredibly contagious virus that can cause serious illness in young infants and children. Within the first year of life, approximately two in three infants experience an RSV infection, with almost all infected before the age of two.

While most infections result in mild symptoms like runny nose, coughing and fever, RSV is the leading cause of hospitalizations for infants under one. Some infections can progress into a severe illness called lower respiratory tract disease (LRTD) – especially those experiencing an infection for the first time – which is responsible for almost 600,000 cases each year that require medical treatment.

Earlier this year, Sanofi and AstraZeneca’s antibody-based drug Beyfortus (nirsevimab-alip) earned fast-tracked approval from the FDA to prevent LRTD in babies and toddlers. Now, the approval of Pfizer’s Abrysvo provides another preventative approach – an RSV vaccine administered at 32–36 weeks of pregnancy to protect infants from birth through their first 6 months of life.

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“Newborns and young infants – whose immune systems are still developing and are not yet strong enough to defend against infections – may now be protected from RSV from the moment of birth through maternal immunization,” said Prof. Eric A.F. Simões, clinical professor of pediatrics and infectious diseases at the University of Colorado School of Medicine. “The approval of Pfizer’s Abrysvo is a major triumph as it helps ensure no delay in potential RSV protection during an infant’s most vulnerable first six months of life and offers healthcare providers a new opportunity to help prevent severe RSV.”

Protection at six months

The FDA’s decision to approve Abrysvo, designed to protect against RSV strains A and B, comes off the back of Phase 3 clinical trial including over 7,000 pregnant individuals and their infants – a total of over 14,000 trial participants.

The randomized, double-blinded and placebo-controlled MATISSE trial, published in the New England Journal of Medicine, showed the treatment to be safe and effective in preventing LRTD in infants born to healthy individuals who were vaccinated during pregnancy.

During the trial, participants were vaccinated at 24–36 weeks gestation with either Abrysvo or a placebo, with the investigators monitoring to see how this affected RSV-associated LRTD in infants at 90, 120, 150 and 180 days after birth.

At 90 days, 6 infants from the vaccine group and 33 infants from the placebo group received medical treatment for severe RSV-associated LRTD. This indicates that the vaccine group had an 82% lower risk of the disease within 90 days after birth, which later waned to 69% within 180 days after birth.

Narrowing the data down to those treated at 32–36 weeks of gestation (1,500 received Abrysvo, 1,500 received a placebo), the range for which Abrysvo is now approved, treatment reduced the risk of severe LRTD by 91% within 90 days of birth, and by 77% within 180 days.

Side effects commonly reported by those who received Abrysvo were pain at the injection site, headaches, muscular pain and nausea. Additionally, a dangerous pregnancy disorder known as pre-eclampsia occurred in 1.8% of Abrysvo-treated participants compared to 1.4% of participants in the placebo group, while preterm birth occurred at a higher rate in the Abrysvo group (5.7%) compared to the placebo group (4.7%). These findings have prompted the FDA to require additional post-marketing studies to investigate the risks of preterm birth and pre-eclampsia.

“Abrysvo’s approval as the first and only maternal immunization to help protect newborns immediately at birth through six months from RSV marks a significant milestone for the scientific community and for public health,” said Dr. Annaliesa Anderson, senior vice president and chief scientific officer of vaccine research and development at Pfizer. “We are incredibly grateful to the clinical trial participants and study investigator teams around the world, as well as our Pfizer colleagues, for their commitment to making this vaccine available. Today, a long-sought-after goal to deliver a maternal vaccine that will help protect infants six months of age or younger – when they are at greatest risk of possible serious consequences from RSV – has been achieved.”

This article is a rework of a press release issued by Pfizer. Material has been edited for length and content.