The drug nirsevimab is safe and offered high protection against respiratory syncytial virus (RSV) in healthy infants three months of age and older during the first season of the virus experienced by these infants and for the entire duration of the seasonal period.
Protection for any medical care for respiratory disease in children who received treatment was 74.5%. For hospitalization, the effectiveness rate was 62.1% compared to the control group.
This is the main finding of a study with 1,490 children to evaluate the action of the drug against this, which is the main causative agent of childhood respiratory infections.
The babies were divided into three groups to receive a single injection of the drug with 50 mg or 100 mg, according to the child’s weight, or placebo (a substance that is harmless to the body). The evaluation of safety and efficacy of the treatment took place for a period of up to 361 days.
The results of the randomized, quadruple-early, phase 3 controlled clinical trial (neither the researchers, participants, healthcare professionals, and advisory committee were aware of who received which substance) were published last Wednesday (2) in the scientific journal The New England Journal of Medicine (Nejm).
Respiratory syncytial virus is the main causative agent of bronchiolitis and pneumonia in children under one year of age. It is highly contagious and can cause seasonal epidemics of respiratory illness in children.
Nirsevimab is a monoclonal antibody that prevents the virus from penetrating cells. The drug was developed in partnership by pharmaceutical companies AstraZeneca and Sanofi.
Until now, the only drug available against the virus was palivizumab, produced by pharmaceutical company AstraZeneca, indicated only for severe cases of respiratory infections, with a high risk of hospitalization.
Trial data with nirsevimab, therefore, are promising, as the drug was highly effective in healthy children, not just those at high risk, and for all ages.
The researchers evaluated the effectiveness of the drug by age group, aged less than or equal to three months, from three to six months and from more than six months.
For children who received nirsevimab, 12 of 994 (1.2%) had RSV respiratory infection, versus 25 of 496 (5%) of those who received placebo.
Over time, the risk of needing medical attention for a respiratory infection was about 77% lower in babies treated with the drug. This means that 8 out of 10 children with HIV infection treated with the drug did not need medical attention.
Relative to one hospitalization of any cause associated with RSV infection, the drug’s efficacy was 59%. Analysis by age, however, showed less efficacy in children younger than three months, but this may have been biased by the relatively small number of babies in this age group or by their low weight, who received the lower dose.
Regarding the safety profile, the most common side effects were mild, and there were no serious adverse events.
Unlike vaccines, monoclonal antibodies are used for treatment after an infection — they are not used to prevent an infection or to induce an immune response.
Unlike the drug palivizumab, however, nirsevimab maintained elevated blood antibody levels even 150 days after use.
The study’s lead investigator and professor of pediatrics at Northwest University Feinberg School of Medicine, William Muller, said the new findings add to the results of the group’s early studies, including a phase 2 study of babies who were born prematurely, whose calculated effectiveness in preventing RSV disease was 70.1%.
“Taken together, the new data and the data available to date support the use of nirsevimab for RSV prevention in all infants, those at greatest risk for serious illness – such as those born prematurely or those with congenital heart problems – and those who are healthy. “, he explained.
The study has some limitations. One is that the trial, conducted simultaneously in several countries including the United States, France, Argentina and South Africa, was largely affected by the Covid-19 pandemic. With the lockdown regime adopted by some countries in 2020, the research had to be paused.
In addition, protective measures to contain the spread of the coronavirus, such as wearing masks and physical distancing, have also impacted the circulation of other respiratory viruses, including RSV.
Muller, however, said he believes this should not influence the drug’s effectiveness. “There’s no reason to think the efficacy found will change in different parts of the world,” she said.
As for the search for an immunizer capable of preventing RSV infection, and not just treating it, the pediatrician says there is hope.
“There is no simple answer, but at the moment there are several research efforts around the world to develop vaccines against respiratory syncytial virus capable of preventing infection either by immunizing the mother, passing the antibodies through the placenta, or by injecting the babies directly” , said.
The doctor hopes that the drug will be developed widely and accessible to populations around the world.
The research was coordinated by physicians from the Stanley Manne Pediatric Research Institute, Ann and Robert Lurie Children’s Hospital in Chicago (USA), and has collaboration with researchers from AstraZeneca and the University of Cape Town, South Africa.
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