Viral vaccine against respiratory syncytial virus in research.
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On Thursday, the U.S. Food and Drug Administration’s Independent Advisory Panel recommended full approval of Pfizer’s vaccine that protects infants against respiratory syncytial virus, but raised safety concerns regarding premature births that could be linked to the shooting.
The committee unanimously said that the data on the effectiveness of the vaccine were sufficient. Ten of the advisers said Pfizer’s vaccine safety data was adequate, while four said it was not.
“If the vaccine actually lives up to the data we’ve seen today, I can guarantee that many infants and their parents will breathe easier in the years to come,” said Dr Jay Portnoy, medical director of the Children’s Mercy Hospital in Kansas City, after voting in favor of the safety and efficacy of the vaccine.
Dr Paul Offit, a vaccine expert at Children’s Hospital of Philadelphia, said he didn’t believe there was enough data to indicate the vaccine’s safety was “reassuring”.
“If you somehow risk premature births with this vaccine, I think there will be a big price to pay,” said Offit, who voted against the vaccine’s safety data.
Adam Berger, director of clinical research policy and health care at the National Institutes of Health, voted in favor of the safety and efficacy of the vaccine, but said post-marketing studies by Pfizer must examine the risk of premature births.
Post-marketing refers to studies conducted on a product after it has received FDA approval.
The FDA generally follows the advice of its advisory committees, but is not required to do so. The agency is expected to make a final decision on the firing in August, just before the RSV season in the fall.
If approved, Pfizer’s vaccine would become the world’s first vaccine that protects infants against RSV, a goal scientists have been working toward for decades.
Earlier this month, the FDA approved GlaxoSmithKline’s first RSV vaccine for adults 60 and older. The agency is expected to make a decision within weeks on Pfizer’s other RSV vaccine for this same age group.
RSV is a common respiratory infection that causes cold-like symptoms. The elderly and young children are particularly vulnerable to more serious RSV infections.
Every year the virus kill 6,000 to 10,000 elderly people and a few hundred children under age 5, according to the Centers for Disease Control and Prevention. About one in 100 children younger than 6 months with RSV infection may need to be hospitalized, the CDC said.
Pfizer’s infant vaccine is given to pregnant women at the end of their second or third trimester. The single-dose vaccine triggers antibodies that are transmitted to the fetus, providing protection against RSV from birth until the first six months of life.
Weighing Safety and Efficacy Data
A phase three trial found that Pfizer’s vaccine was nearly 82% effective in preventing serious illness caused by RSV in newborns during the first 90 days of life. The vaccine was also about 70% effective in the baby’s first six months of life.
But the advisory committee’s concerns stemmed from the safety data from that trial.
A slightly higher number of preterm births occurred among mothers who took the vaccine compared to those who received a placebo: 5.7% versus 4.7%, respectively.
Pfizer and the FDA said the difference does not appear to be statistically significant.
Most infants, even born prematurely, also delivered after 34 weeks of pregnancy, just weeks away from their due date.
But Dr. Hana El Sahly, who chairs the FDA’s advisory committee, said that “even though it’s late preterm labor, the fact that we’re putting them into preterm labor while we’re sitting here at intellectually debating the issue is not trivial”.
Premature labor is not a new issue when it comes to RSV vaccines for infants.
Pfizer rival GSK halted its own trial of its RSV vaccine for newborns after noticing concerning the data on premature births and neonatal deaths, or when a baby dies within the first 28 days of life.
Offit also said GSK’s trial “suspended” Pfizer’s RSV vaccine for infants.
“If GSK really abandons a program on a similar, almost identical vaccine, it will weigh on [Pfizer’s] program,” he told the meeting. “I think that needs to be addressed.”
Portnoy added that premature deliveries could potentially dampen the benefits of the shot.
“The problem is that if the child is born earlier, it also reduces the effectiveness of treatment because earlier birth means fewer antibodies are transferred,” he said. “So it’s a very complex thing because now the harm makes the benefit less. There’s an interaction between the two.”
But some panel members questioned whether there was a clear causal relationship between the vaccine and preterm birth.
“Am I concerned about the imbalance of premature births? Yes. Am I convinced it’s real? No,” said Dr. Daniel Feikin, scientific adviser and consultant in respiratory diseases, who voted in favor of safety of the vaccine.
Pfizer representatives also pushed back on safety concerns, stressing that the benefits of the vaccine outweigh the risks.
“Certainly, in our view, there is no definitive evidence to suggest that there is a risk of prematurity,” said Dr. William Gruber, senior vice president of clinical vaccine research and development at Pfizer. “So the question is, are you holding the potential benefits of the vaccine hostage to something that you have no statistical significance at this point?”
Some of the participants’ children also had low birth weight and developmental delays, FDA staff said.
Most of the more than 3,000 mothers who received the vaccine in the trial experienced mild to moderate adverse effects, according to FDA staff’s review of the data.
The most common reactions were fatigue, muscle aches, headaches and pain at the injection site. Most reactions resolved within three to four days of vaccination, the staff review noted.