FDA Advisor OK AstraZeneca, Sanofi Toddler Antibodies Towards RSV

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A panel of independent advisors to the Food and Drug Administration on Thursday unanimously recommended approval of the antibody nirsevimab to protect infants from respiratory syncytial virus, the leading cause of hospitalizations in newborns.

If the FDA approves nirsevimab, the antibody would be the first medical intervention available in the US that can protect all infants from RSV. The FDA, which is not required 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 from AstraZeneca. The drug would be marketed by Sanofi.

The Advisory Board voted 21-0 to recommend its approval.

In a separate vote, the consultants also recommended the use of nirsevimab in children up to two years old who remain susceptible to the virus even in their second RSV season. The vote resulted in 19:2.

RSV kills nearly 100 babies each year in the United States.

Infants hospitalized with RSV often require oxygen support, IV fluids, and are sometimes put on a ventilator to support their breathing.

The virus poses a major public health threat. A surge in RSV infections over the past year has overwhelmed children’s hospitals and prompted calls for the Biden administration to declare a public health emergency in response.

RSV circulates at the same time as the flu and Covid-19, putting additional strain on hospitals.

There is another monoclonal antibody against RSV called palivizumab. However, this antibody is only intended for premature babies and those with lung and congenital heart disease who are at high risk of serious illness. Palivizumab must also be administered monthly.

Nirsevimab, on the other hand, would also be given to healthy infants, who make up the majority of hospital admissions. It is also administered as a single dose, which would make it easier to administer.

Nirsevimab is not considered a vaccine because it is a monoclonal antibody.

It’s unclear whether the federal Vaccines for Children program will make nirsevimab available for free to uninsured and underinsured children because the antibody is regulated as a drug.

Nirsevimab is already approved in Canada, Europe and the UK.


According to an FDA review, nirsevimab was up to 75% effective in preventing lower respiratory tract infections that required medical attention and 78% effective in preventing hospitalizations.

A more conservative FDA estimate puts 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.

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Nirsevimab is given as a single injection, with the dose depending on the baby’s weight. Infants weighing less than 5 kilograms would receive a 50 mg injection in their first RSV season, and infants weighing 5 kilograms or more would receive a 100 mg injection.

Children under the age of two who remain at risk for severe RSV into the second season would receive a single 200 mg injection of nirsevimab.


The FDA found no safety concerns in its review of nirsevimab.

Other monoclonal antibodies have been associated with serious 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 rare in infants who received the antibody. But dr Melissa Baylor, an FDA official, said cases of these side effects would likely occur if nirsevimab were approved.

Twelve infants receiving nirsevimab in the studies died. According to the FDA review, none of these deaths were related to the antibody.

Four died of heart disease, two died of gastroenteritis, two died of unknown causes but they were likely cot deaths, one died of a tumour, one died of Covid, one died of a skull fracture and one died of a Lung infection.

“Most of the deaths were due to an underlying condition,” Baylor said. “None of the deaths appeared to be related to nirsevimab.”

Due to historical mistakes in RSV vaccine development, much attention is paid to safety. Scientists first tried to create a vaccine using an inactivated virus in the 1960s, but that shot made RSV disease worse in some children when they got their first natural infection, resulting in the deaths of two infants.

Manish Shroff, head of patient safety at AstraZeneca, said the company will be closely monitoring the safety of nirsevimab through a large global monitoring system: “Safety is paramount,” he said.

Baylor said there were also unanswered questions about how nirsevimab would interact with vaccines in development that give the fetus protective antibodies by administering the vaccine to the mother.

“It is unclear whether giving nirsevimab to infants whose mothers have received such RSV vaccines provides additional protection or poses potential safety issues,” Baylor said.

FDA advisers in May endorsed Pfizer’s maternal RSV vaccine, which protects infants. The agency is expected to make a decision on Pfizer’s vaccination in August.

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