RSV Cases Flood Children’s Hospitals as Pfizer Announces Promising Vaccine

After producing strong clinical trial results for its respiratory syncytial virus (RSV) vaccine, Pfizer says it is ending enrollment in its study and preparing to submit for FDA approval.

The Phase 3 clinical trial MATISSE tested a bivalent RSV vaccine in pregnant study participants and found it successfully protected infants from RSV disease after birth. Results showed 81.8% efficacy against severe medically attended lower respiratory tract infection due to RSV infection from birth through the first 90 days of life and 69.4% efficacy through the first 6 months of life.

The trial enrolled 7,400 pregnant individuals randomizing them in a 1:1 ratio between an experimental group and a placebo group. Statistical success for the trial’s secondary endpoint, clinically meaningful efficacy, was not reached. Pfizer reported no safety concerns for vaccinated mothers and their babies.

“We are thrilled by these data as this is the first-ever investigational vaccine shown to help protect newborns against severe RSV-related respiratory illness immediately at birth,” said Annaliesa Anderson, PhD, Senior Vice President and Chief Scientific Officer, Vaccine Research & Development, Pfizer. “We look forward to working with the FDA and other regulatory agencies to bring this vaccine candidate to expectant mothers to help protect their infants against severe RSV during their most vulnerable first six months of life, which has the highest burden of RSV illness in infants.”

Most cases of RSV resolve within two weeks without medical intervention. Symptoms of the illness include fever, wheezing, and sneezing, usually appearing a few days after infection. 

The positive trial results come as an RSV surge whips through the US, threatening infants and the elderly. According to CDC tracking data, the cumulative RSV hospitalization rate is up to 2.9 per 100,000 individuals for the 2022­­­–2023 season compared to a rate of 1.9 per 100,000 in 2021–2022.

In Massachusetts, Boston Children’s Hospital reduced elective procedures as RSV cases spiked. Across the country, in Orange County, California, officials declared a public health emergency in response to unprecedented numbers of RSV cases.

The most recent data from the Department of Health and Human Services indicate that almost 75% of pediatric hospital beds are now full.

While RSV cases continue to rise, the CDC is also warning healthcare providers about the uptick in enterovirus D68 (EV-68). In August, CDC surveillance found higher-than-average rates of EV-68, which can lead to severe neurological conditions in a small portion of cases.

In addition to their RSV vaccine, Pfizer recently acquired ReViral and the company’s portfolio of RSV therapeutics. ReViral’s therapeutic candidates focus on treating RSV infection in older adults who are more likely to die due to RSV infection than children.