New RSV Vaccine Will Cut Hospitalizations,
Study Shows

Megan Brooks

October 12, 2023

The newly approved respiratory syncytial virus vaccine administered during pregnancy substantially reduces the clinical and economic burden of lower respiratory tract disease caused by RSV, according to research presented at Infectious Disease Week (IDWeek) 2023 Annual Meeting.

"With RSV maternal vaccination that is associated with clinical efficacy of 69% against severe RSV disease at 6 months, we estimated that up to 200,000 cases can be averted, and that is associated with almost $800 million in total," presenting author Amy W. Law, PharmD, director of global value and evidence at Pfizer, pointed out during a news briefing.

"RSV is associated with a significant burden in the US and this newly approved and recommended maternal RSV vaccine can have substantial impact in easing some of that burden," Law explained.

This study is "particularly timely as we head into RSV peak season," said briefing moderator Natasha Halasa, MD, MPH, professor of pediatrics, Division of Pediatric Infectious Diseases at Vanderbilt University in Nashville, Tennessee.

The challenge, said Halasa, is that uptake of maternal vaccines and vaccines in general is "not optimal," making increased awareness of this new maternal RSV vaccine important.

Strong Efficacy Data

Most children are infected with RSV at least once by the time they reach age 2 years. Very young children are at particular risk of severe complications, such as pneumonia or bronchitis.

As reported previously by Medscape Infectious Diseases, in the randomized, double-blind, placebo-controlled phase 3 study, Pfizer's maternal RSV vaccine had an almost 82% efficacy against severe RSV infection in infants from birth through the first 90 days of life.

The vaccine also had a 69% efficacy against severe disease through the first 6 months of life. As part of the trial, a total of 7400 women received a single dose of the vaccine in the late second or third trimester of their pregnancy. There were no signs of safety issues for the mothers or infants.

Based on the results, the US Food and Drug Administration approved the vaccine, known as Abrysvo, in August, to be given between weeks' 32 and 36 of pregnancy.

New Modeling Study

Law and colleagues modeled the potential public health impact — both clinical and economic — of the maternal RSV vaccine among the population of all pregnant women and their infants born during a 12-month period in the US. The model focused on severe RSV disease in babies that required medical attention.

According to their model, without widespread use of the maternal RSV vaccine, 48,246 hospitalizations, 144,495 emergency department encounters, and 399,313 outpatient clinic visits related to RSV are projected to occur annually among the US birth cohort of 3.7 million infants younger than 12 months.

With widespread use of the vaccine, annual hospitalizations resulting from infant RSV would fall by 51%, emergency department encounters would decline by 32% and outpatient clinic visits by 32% — corresponding to a decrease in direct medical costs of about $692 million and indirect nonmedical costs of roughly $110 million.

Law highlighted two important caveats to the data. "The protections are based on the year-round administration of the vaccine to pregnant women at 32 to 36 weeks' gestational age, and this is also assuming 100% uptake. Of course, in reality, that most likely is not the case," she told the briefing.

Halasa noted that the peak age for severe RSV illness is 3 months and it's tough to identify infants at highest risk for severe RSV.

Nearly 80% of infants with RSV who are hospitalized do not have an underlying medical condition, "so we don't even know who those high-risk infants are. That's why having this vaccine is so exciting," she told the briefing.

Halasa said it's also important to note that infants with severe RSV typically make not just one but multiple visits to the clinic or emergency department, leading to missed days of work for the parent, not to mention the "emotional burden of having your otherwise healthy newborn or young infant in the hospital."

In addition to Pfizer's maternal RSV vaccine, the FDA in July approved AstraZeneca's monoclonal antibody nirsevimab (Beyfortus) for the prevention of RSV in neonates and infants entering their first RSV season, and in children up to 24 months who remain vulnerable to severe RSV disease through their second RSV season.

The study was funded by Pfizer. Law is employed by Pfizer. Halasa has received grant and research support from Merck.

Infectious Disease Week 2023 Annual Meeting: Abstract 1942. To be presented October 13, 2023.

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