Two studies published today show more promising evidence that the respiratory syncytial virus (RSV) antibody, nirsevimab, is an effective way to protect infants from illness.
Protection against infection, co-infection
The first study, published yesterday in Clinical Infectious Diseases, includes results of a phase 3 clinical trial (MELODY), which show that the monoclonal antibody protects against single RSV and RSV co-infections, with no evidence of replacement of RSV with other respiratory viruses.
The trial was a randomized, double-blind, placebo-controlled, phase 3 study of nirsevimab in healthy-term and late-preterm (older than 35 weeks) infants entering their first RSV season. Of 3,012 participants, 2,009 received nirsevimab as a single injection, and 1,003 received a placebo.
All participants were followed up, and researchers collected nasopharyngeal swabs for any infants with symptoms of lower respiratory tract infections. In total 519 swabs from 337 nirsevimab participants and 333 swabs from 224 placebo participants were tested for RSV or other viruses.
Rhinovirus/enterovirus, detected in over half of samples, was the most common virus detected in the study. Most of the study authors are scientists for AstraZeneca, which makes nirsevimab under the trade name Beyfortus.
RSV detections lower in treatment group
Rates of RSV detections were significantly lower in the treatment group compared to controls. There were 24 cases of RSV infection through day 151 in the nirsevimab arm and 54 in the placebo arm, the authors wrote. Of note, 7 (30.4%) and 16 (33.3%), respectively, were co-infections with RSV and another pathogen.
For both control and treatment groups, 70% of RSV infections were mild, and 25% required hospitalization.
The researchers noted that nirsevimab treatment led to a lower incidence of RSV infections over time versus placebo without viral replacement, or no increased incidence of other viral infections.
"The lower incidence rates of RSV infection in nirsevimab recipients versus placebo, coupled with similar incidences of non-RSV respiratory viruses between nirsevimab and placebo participants, further support the nirsevimab-specific prevention of RSV and suggest there is no replacement of RSV with other viruses following nirsevimab administration," the authors concluded.
Early administration of nirsevimab common
In a second study, published today in Morbidity and Mortality Weekly Report, New York City Health Department researchers show that nearly half of infants born in New York City shortly before or during the last RSV season and who received nirsevimab got it during their first 7 days of life.
The study included children who were both eligible and ineligible for Vaccines for Children (VFC).
Per recommendations made by the Advisory Committee on Immunization Practices in 2023, nirsevimab should be given to infants aged 7 months old and younger and to infants and children aged 8 to 19 months who have risk factors for severe RSV disease, shortly before the RSV season, or within the first week of life if born during October through March in most of the United States.
Overall, 15,521 nirsevimab doses were administered to infants and children aged 0 to 19 months in New York City before the 2023-20 RSV season. Forty-five percent received nirsevimab within the first 7 days of life: 37% of VFC-eligible infants, 45% of non–VFC-eligible infants and children, and 61% of infants whose VFC eligibility was missing or unknown.
Entering the 2024–25 RSV season, an adequate supply of nirsevimab will be important to continue to protect infants and children.
"Entering the 2024–25 RSV season, an adequate supply of nirsevimab will be important to continue to protect infants and children," the authors wrote.
