A new respiratory syncytial virus (RSV) the vaccine protected newborns against severe cases of the disease in the critical months immediately after birth, drugmaker Pfizer announced (opens in a new tab) Tuesday (November 1). The single-dose vaccine was given to pregnant women during their second or third trimester, which triggered the production of protective antibodies which then crossed the placenta.
The company monitored the infants in the trial for six months after birth and found that during this time the vaccine was 69.4% effective in preventing severe cases of RSV that would require medical attention. However, firing efficiency was higher – about 81.8% – during the first three months of life.
This drop in immunity follows a pattern seen with other vaccines given during pregnancy, such as those against tetanus and whooping coughwhich was described in a 2021 report in the journal JAMA Pediatrics (opens in a new tab). Usually vaccine-induced antibody decline rapidly during the first two months of life, then decline steadily over the next four to eight months.
Positive results from Pfizer’s trials have not yet been peer-reviewed, but the company plans to submit the data to a scientific review, according to the statement. The drugmaker also plans to seek US Food and Drug Administration (FDA) approval by the end of 2022.
Related: How to Get Pregnant: Tips and Facts to Increase Fertility
RSV usually causes mild colds in healthy children and adults, but virus can cause serious illness in infants less than 1 year old and adults over 65 years old, according to the Centers for Disaster Control and Prevention (opens in a new tab) (CDC). The infection can migrate from the upper respiratory tract to the lungs, triggering inflammation in the air sacs of the lungs (pneumonia) or the small airways of the organs (bronchiolitis). This inflammation can easily compromise infant breathing by restricting their tiny airways.
According to CDC (opens in a new tab). This year’s RSV season has started early and aggressively, and doctors have already seen an increase in cases in emergency rooms and pediatric intensive care units, NPR reported (opens in a new tab).
“We really hope that everything can be done in time to vaccinate mothers before the next RSV season,” Annaliesa Anderson, scientific director of vaccine research and development at Pfizer, told The Washington Post. (opens in a new tab). “We are about to enter a very intense RSV season. We are seeing hospitals fill up. Everyone appreciates the urgency that can really help prevent this.”
Pfizer’s vaccine contains crystallized “F” proteins, which RSV viruses use to enter human cells. The shot carries two versions of the F protein, representing the two main RSV subgroups: subgroups A and B. These proteins are locked into the shape they take just before fusing with a cell.
The recent trial included 7,400 pregnant women, aged 49 and under, who received either the RSV vaccine or a placebo at the end of their second or third trimester. The trial covered 18 countries and began in June 2020, meaning it covered multiple RSV seasons in both hemispheres, according to Pfizer’s statement.
The statement also noted that the injections were “well tolerated with no safety concerns for those vaccinated and their neonates.”
As new maternal RSV vaccines head toward FDA approval, there’s also good news about an RSV vaccine for the elderly. Pfizer announced equally positive results (opens in a new tab) of its late-stage trial in people aged 60 and over in August.