"Remarkable" results for new maternal RSV vaccine in Phase 3 trial
After decades of research a long-awaited vaccine against respiratory syncytial virus (RSV) may finally be here. Preliminary Phase 3 data has revealed maternal immunization with a new vaccine delivered extraordinary protection from severe disease in babies across their first few months of life.
RSV is a very common cause of respiratory illness in children, but for newborns the virus can be life-threatening. In a child's first few months of life RSV can frequently lead to severe lung disease and sometimes death.
Scientists have long sought to develop a vaccine against RSV, but a disastrous trial in the 1960s slowed research for decades. That vaccine was an inactivated version of the whole virus but instead of protecting children from infections it actually made them sicker.
Since then researchers have slowly and cautiously been working to produce more targeted RSV vaccines. This new vaccine, being developed by Pfizer, is based on landmark research from a decade ago that described one of the key proteins on the surface of RSV.
Known as the F protein, one of the challenges researchers faced in developing an effective RSV vaccine was that this protein tends to shape-shift when it fuses with a human cell. So this new vaccine focused on training the immune system to recognize the protein in its "prefusion" form.
Earlier this year Pfizer reported preliminary Phase 3 results testing this vaccine, dubbed RSVpreF, in adults aged over 60. Those results revealed the vaccine is 85% percent effective at preventing severe disease in older adults, but plenty of focus was on another large trial testing the vaccine in pregnant women to see if protection was delivered to newborn babies.
These early results, not yet published in any peer-reviewed journal, found a single dose of the vaccine given near the end of the second trimester of pregnancy led to impressive protection of newborns up to six months. The maternal vaccination reduced rates of severe medically attended lower respiratory tract illness due to RSV by 81.8% across the first three months of life. Across the first six months of life that efficacy held at 69.4%.
“It is an absolute game-changer and of high global importance," said Chrissie Jones, a pediatric infectious disease researcher from the University of Southampton. "This data shows that a vaccine against RSV given to pregnant women could substantially reduce the burden of severe RSV disease in young infants. What is remarkable about this data is that high efficacy is still since up to six-months of age."
On a secondary endpoint, preventing less severe medical interventions such as doctor visits due to respiratory illness, the vaccine was slightly less successful, only hitting around 50% efficacy compared to placebo. While this is reportedly lower than a threshold previously specified by the FDA for approval, Pfizer has indicated the other datapoints are likely more than enough to get the vaccine over the line and authorized for wider clinical use.
Beyond the vaccine's acute benefits in preventing severe disease or death, research is ongoing to understand whether it reduces a child's risk of chronic lung problems triggered by RSV infection early in life. Barney Graham, one of the scientists who worked on the foundational RSV protein studies a decade ago, told Science recently that improving general long-term lung health in children was always one of the biggest hopes for the vaccine.
"If they’re infected with RSV very early in life and develop severe disease, that affects their lung development and overall lung health probably for their lifetime," said Graham. "So the goal here is to really improve overall lung health and that is something that’s hard to calculate until you’ve seen it evolve over several years."