Pfizer Inc said on Tuesday its experimental respiratory syncytial virus (RSV) vaccine was found effective for preventing severe infections in infants after being given in a late-stage study to expectant mothers in the second half of pregnancy.
Pfizer's shot, if approved, could be the first maternal vaccine available to relieve the burden of the disease in young infants. The company stopped the trial after the early success and plans to file for approval by the end of 2022.
"Maternal immunization takes advantage of the ability to protect the infant from day one... which is important because the peak of hospitalization in these infants due to RSV is around one to two months of age," Kena Swanson, Vice President of Viral Vaccines at Pfizer, said in an interview.
The vaccine did not meet the study's second main goal of preventing less severe respiratory illness, the company said.
Companies such as Pfizer and GSK Plc are racing to develop a vaccine against RSV, a leading cause of pneumonia in toddlers and older adults. An effective shot should generate billions of dollars in sales upon approval.
Federal data estimates that RSV sends 58,000 children under the age of five to U.S. hospitals each year.
Pfizer's vaccine candidate met one of the two primary endpoints of the study, showing 81.8% efficacy in preventing a severe form of lower respiratory tract illness in infants in the first 90 days.
Signs of severe illness in the study included very low oxygen levels, being put on a mechanical ventilator, being placed in an intensive care unit, or being unconscious due to RSV.
The unmet endpoint was for reduction of illness in the infants that necessitated care by a healthcare provider.
RSV infections among young children are rising in the United States. There are currently no approved RSV vaccines. In August, Pfizer had said its RSV vaccine was effective among older adults in a late-stage study.
Rival GSK said in October, its RSV shot was 82.6% effective in a late-stage study involving older adults.
Potential approval of Pfizer's shot for pregnant women as well as adults would make it the "only company to have both a maternal and older adult indication", Pfizer U.S. President Angela Lukin said in a conference call in October.
(Reporting by Raghav Mahobe in Bengaluru and Michael Erman in New Jersey; Editing by David Gregorio)