A Pfizer vaccine that could protect unborn babies from the common seasonal bug respiratory syncytial virus (RSV) has been recommended for approval by advisors to the Food and Drug Administration.
The agency’s expert panel voted unanimously that the shot was effective at preventing severe illness from RSV in infants under six months old on Thursday.
But four out of 14-panel members raised concerns over whether the shot was safe, saying there was evidence that it may raise the risk of premature births.
The vaccine is given as a single dose to pregnant women in the second or third trimester of pregnancy and works by triggering RSV-fighting antibodies that can then be passed on to babies in the womb via the placenta.
The FDA is still set to rule on the shot but could approve it as early as August just before RSV season, making it the world’s first RSV vaccine for infants. It comes after the agency approved the world’s first-ever vaccine for RSV earlier this month.
The FDA’s expert panel voted unanimously that the vaccine was effective, but concerns were raised over its safety profile. A decision from the FDA is expected in August, although it generally follows the advice of its expert panel
Virtually all children catch RSV at least once by the time they are two years old, with most facing a mild, cold-like illness.
But the FDA says that babies under six months old are at particular risk of severe disease from the virus, which may be because their immune systems are still developing or they are not able to cough as forcefully as older children.
Up to one in 50 children in this age group are hospitalized by the virus, the FDA says, facing treatments including IV fluids and mechanical ventilators. A few hundred under five years old die from the infection every year in the US.
The Pfizer vaccine — dubbed RSVpreF — works by exposing the mother to a protein from the surface of RSV, triggering an immune reaction and the production of RSV-fighting antibodies.
These can then enter babies still in the womb via the placenta. They can also be transferred after birth through the colostrum — the first milk that an infant drinks from its mother.
They can persist in an infant for up to six months, boosting defenses as an infant gradually builds up their immune system.
Other vaccines already use this system to trigger immunity in infants, including the flu vaccine and the shot against Whooping Cough.
All 14 members of the FDA’s panel voted that the vaccine was effective at preventing severe disease in infants when administered to pregnant mothers, and ten out of 14 voted that its safety data was ‘generally favorable’ for use in pregnant women.
The FDA will now decide whether to approve the vaccine, but the agnecy normally follows the advice of its expert panel.
Some members raised concerns, however, that the vaccine raised the risk of premature births.
Dr Paul Offit, a vaccine expert at the Children’s Hospital of Philadelphia who has previously raised concerns over the Covid vaccine, said that in general, the safety data was ‘reassuring’.
But he added, reports CNBC, that ‘if you’re in any sense risking premature births with this vaccine, I think there’ll be a big price to pay’.
He also pointed out that GSK had shelved its trials of a similar RSV vaccine in pregnant women after noticing an uptick in preterm births and neonatal deaths, or when a baby dies during the first 28 days of life.
Dr Offit said this move was ‘hanging over’ Pfizer’s own RSV shots for infants.
‘If GSK truly abandons a program on a similar, almost identical vaccine, that is going to hang over [Pfizer’s] program.’
Dr Jay Portnoy, medical director at the Children’s Mercy Hospital in Kansas City who voted in favor of the vaccine’s safety and effectiveness, also warned preterm births could dampen the benefits of the jab.
‘The problem is if the child is born earlier, that also reduces the efficacy of the treatment because earlier birth means less antibodies are transferred,’ he said.
‘So, this is a very complex thing because now the harm actually makes the benefit less so. There’s an interaction between the two.’
Infants who are born prematurely — before week 37 of pregnancy — are at higher risk of many health complications, including respiratory problems, infections and delays in development.
The above graph shows RSV-related hospitalizations in the United States by month and year. They tick up between September and the end of spring — RSV season
The approval was based on data from a phase three trial of the vaccine, which involved 7,400 pregnant women — half of which received the shot while the rest got a placebo.
This showed that it was 82 percent effective at preventing severe disease from RSV in newborns during the first 90 days of life.
The shot was also about 70 percent effective during the first six months of the baby’s life against severe disease.
But the study also showed that there was a higher risk of premature births among mothers who got the shot compared to those who got the placebo.
In the vaccine group, nearly six percent of mothers had a preterm birth, while in the placebo group, the figure was 4.7 percent.
Pfizer said that the difference was not statistically significant, but this has still raised concerns among scientists.
Backing the safety of their vaccine, Pfizer’s senior vice president for vaccine research and development Dr William Gruber, said: ‘Certainly, in our eyes, there is no definitive evidence to suggest there is a risk of prematurity.
‘So the question is, do you hold hostage the potential benefits of the vaccine for something which you have no statistical significance at this point?’