Narisara Nami | Even | Getty Images
A panel of independent advisors to the Food and Drug Administration unanimously recommended on Thursday that the antibody nirsevimab be approved for use to protect infants against respiratory syncytial virus, the leading cause of hospitalization in newborns.
If the FDA approves nirsevimab, the antibody would become the first available medical intervention in the US that can protect all babies against RSV. The FDA, which is under no obligation to follow its advisory panel’s recommendation, is expected to make a final decision on nirsevimab in the third quarter of this year.
Nirsevimab is a monoclonal antibody made by AstraZeneca. The drug would be marketed by Sanofi.
The advisory panel voted 21 to 0 to recommend approval.
In a separate vote, the advisors also recommended the use of nirsevimab in children up to two years old who remain vulnerable to the virus in their second season of RSV. That vote was 19-2.
RSV kills nearly 100 babies in the United States each year.
Babies hospitalized with RSV often require oxygen support, intravenous fluids, and are sometimes placed on a ventilator to assist their breathing.
The virus poses a major threat to public health. A wave of RSV infections last year overwhelmed children’s hospitals, prompting calls for the Biden administration to declare a public health emergency in response.
RSV is circulating at the same time as the flu and Covid-19, putting additional pressure on hospitals.
There is another monoclonal antibody used against RSV called palivizumab. But this antibody is only for premature babies and people with lung and congenital heart disease who are at high risk for serious disease. Palivizumab must also be administered monthly.
Nirsevimab, on the other hand, would also be administered to healthy babies, who account for a majority of hospital admissions. It is also given in a single dose, which would make administration easier.
Nirsevimab is not considered a vaccine because it is a monoclonal antibody.
It’s unclear whether the federal Vaccines for Children program will provide nirsevimab for free to uninsured and underinsured children because the antibody is regulated as a drug.
Nirsevimab is already approved in Canada, Europe and the United Kingdom.
effectiveness
Nirsevimab was up to 75% effective in preventing lower respiratory tract infections requiring medical attention and 78% effective in preventing hospitalizations, according to an FDA review.
A more conservative estimate by the FDA put the antibody’s effectiveness at about 48% against lower respiratory tract infections that required medical attention. This estimate assumed that patients with missing data on their health outcomes had lower respiratory tract infections that required medical attention.
Nirsevimab is given as a single injection where the dose depends on the baby’s weight. Infants weighing less than 5 kilograms will receive a 50 mg injection for their first season of RSV, and infants weighing 5 kilograms or more will receive a 100 mg injection.
Children under two years of age who remain at risk of severe RSV in their second year of life receive a single injection of 200 mg nirsevimab.
Safety
The FDA has not identified any safety concerns in its review of nirsevimab.
Other monoclonal antibodies have been associated with severe allergic reactions, skin rashes and other hypersensitivity reactions.
The FDA found no cases of serious allergic reactions in the nirsevimab studies, and cases of rash and hypersensitivity reactions were low in infants who received the antibody. But dr. Melissa Baylor, an FDA official, said instances of these side effects are likely to emerge if nirsevimab is approved.
Twelve babies who received nirsevimab during the studies died. None of these deaths were related to the antibody, according to the FDA’s assessment.
Four died of heart disease, two died of gastroenteritis, two died of unknown causes but were likely cases of SIDS, one died of tumor, one died of Covid, one died of skull fracture, and one died of pneumonia.
“Most of the deaths were due to an underlying disease,” Baylor said. “none of the deaths appeared to be related to nirsevimab.”
There is a huge focus on safety because of historical failures in RSV vaccine development. Scientists first tried to develop a vaccine with an inactivated virus in the 1960s, but that shot worsened RSV disease in some children when they got their first natural infection, resulting in the death of two babies.
Manish Shroff, head of patient safety at AstraZeneca, said the company will closely monitor the safety of nirsevimab through a large global monitoring system: “Safety is of paramount importance,” he said.
Baylor said there are also unanswered questions about how nirsevimab would interact with vaccines in development that deliver protective antibodies to the fetus by giving the injection to the mother.
It is unclear whether giving nirsevimab to babies whose mothers received such RSV vaccines would provide additional protection or raise potential safety concerns,” Baylor said.
In May, FDA advisers approved Pfizer’s maternal RSV vaccine that protects babies. The agency is expected to make a decision on Pfizer’s shot in August.
