Children's Hospital Colorado

Eric A.F. Simões, MD, Leads Global Study of Maternal Vaccine for the Prevention of Severe RSV in Infants

Children's Hospital Colorado | August 25, 2023

On Aug. 21, 2023, the U.S. Food and Drug Administration (FDA) and Centers for Disease Control and Prevention (CDC) announced the approval of Pfizer’s ABRYSVOTM, a vaccine for the prevention of severe respiratory syncytial virus (RSV) in infants through maternal immunization. The global clinical study was led by Eric A.F. Simões, MD, infectious disease expert at Children's Hospital Colorado, Clinical Professor of Pediatrics at the University of Colorado School of Medicine and Professor of Epidemiology at the Colorado School of Public Health.

How serious is RSV?

RSV is a common virus that can be mistaken for a common cold in adults but can be extremely serious in infants and young children, as well as older adults. RSV is the leading cause of hospitalization of sick infants in U.S.; the leading cause of lower respiratory infections in children, such as bronchiolitis and pneumonia; and a major cause of outpatient visits, emergency department visits and hospitalizations worldwide. Globally it is estimated that RSV kills more than 100,000 infants annually, mostly in developing countries.

In the U.S., approximately 500,000 to 600,000 infants less than 12 months of age experience medically attended lower respiratory tract diseases (MA-LRTD) due to RSV each year. This vaccine helps prevent MA-LRTD and severe MA-LRTD caused by RSV in infants, from birth up to six months of age, by immunizing pregnant individuals.

In 2022, Children’s Colorado experienced record volumes of patients with respiratory illnesses in its emergency departments, with inpatient units and intensive care units operating at or above maximum capacity for several weeks

How does the RSV vaccine help?

This vaccination has the opportunity to substantially reduce the burden of severe RSV not only in high-income countries but also in developing countries where it has the potential to reduce significant infant mortality from the disease,” Dr. Simões said. “It will also significantly reduce the cost burden of medical visits, hospitalizations and missed parental workdays.”

Overview of RSV vaccine study

The FDA’s decision is based on data from a clinical trial in 7,400 maternal/infant pairs (14,800 participants) from 18 countries spanning four RSV seasons. Eighty of these maternal/infant pairs were studied at the University of Colorado Anschutz Medical Campus and Children’s Colorado. The trial started in June 2020, with vaccinations administered when moms were between 24-36 weeks pregnant. The vaccinated were followed for six months thereafter, and their babies were followed 12-24 months after, with parental consent.

The study investigated whether protective antibodies would transfer to the babies in utero, through the placenta, and protect them against RSV LRTD in the first year of life. The study showed a protective rate of 81.8% within 90 days after birth and 69.4% within 180 days after birth against severe RSV disease, compared to mothers who did not receive the vaccine.

“This proves higher rates of protection happening in younger, more at-risk babies,” Simões said.

FDA Approval Process for the RSV Vaccine

FDA approval is an extremely thorough process. Once a pharmaceutical company has evidence that a drug is safe and effective for its intended use, it submits an application to the FDA. The FDA review team examines all submitted data and makes a decision to approve it or not.

The FDA's Vaccines and Related Biological Products Advisory Committee (VRBPAC) provides independent expert advice to the FDA to help make a decision. In this case, the VRBPAC voted unanimously that the available data supported the efficacy of this maternal vaccination to protect against the complications of RSV in infants from birth to six months of age. Once approved, the Advisory Committee on Immunization Practices will make recommendations for vaccine use. The recommendation then must be approved by the CDC director to become CDC public health guidance.

Vaccine education begins with the OB/GYN

This vaccine will be administered between 32- and 36-weeks gestation. Fifty percent of hospitalizations due to respiratory illnesses in children under one year of age are due to RSV.  This is all despite naturally occurring maternal antibodies. 

“Vaccines given to patients during pregnancy increase the maternal antibody protection to such levels that these antibodies cross the placenta and provide protection for babies during the first few months of life,” said Christine Conageski, MD, associate professor in the Department of Obstetrics and Gynecology (OB/GYN) at the University of Colorado School of Medicine. “We’ve used this same strategy to protect infants against pertussis, influenza and tetanus for years.”

By recruiting individuals from across 18 countries in both the northern and southern hemispheres, the recruitment team at University of Colorado School of Medicine has demonstrated this vaccine is likely of benefit to all pregnant people and their infants. This trial could not have happened without the collaboration and support of the University of Colorado OB/GYN recruitment and care team, the UCHealth Labor & Delivery unit, and neonatologists and researchers at Children's Colorado. Together, the study demonstrated that not only is the vaccine effective, but it is also safe.

It is always important to discuss vaccines with your provider to determine if a vaccine is right for you.

Hope for future respiratory seasons

Simões believes now is the time for families to be educated about RSV and that this vaccine is the next step in protecting babies from the dangers of the illness. 

“After the respiratory season we had last year, where we had to actually stop all non-emergency surgeries to make room for the young patients coming in with RSV, Children’s Colorado, pediatricians and all of us working on RSV prevention for the last 40 or so years, are extremely excited for this next chapter,” Simões said.