Two recent studies provide further evidence supporting the effectiveness of nirsevimab in protecting infants from respiratory syncytial virus (RSV) illness. The findings highlight the monoclonal antibody's ability to prevent RSV infections and co-infections without leading to viral replacement.
Nirsevimab Protects Against RSV and Co-infections
A phase 3 clinical trial (MELODY), published in Clinical Infectious Diseases, assessed the efficacy of nirsevimab in healthy-term and late-preterm infants (older than 35 weeks) entering their first RSV season. The randomized, double-blind, placebo-controlled study involved 3,012 participants, with 2,009 receiving a single injection of nirsevimab and 1,003 receiving a placebo.
Researchers collected nasopharyngeal swabs from infants exhibiting symptoms of lower respiratory tract infections. Out of 519 swabs from 337 nirsevimab participants and 333 swabs from 224 placebo participants, rhinovirus/enterovirus was the most commonly detected virus. The study revealed significantly lower rates of RSV detection in the nirsevimab group compared to the placebo group, with 24 cases in the nirsevimab arm and 54 in the placebo arm through day 151. Approximately 30.4% and 33.3% of these cases, respectively, were co-infections with RSV and another pathogen.
Notably, around 70% of RSV infections were mild in both groups, while 25% required hospitalization. The study indicated that nirsevimab treatment led to a lower incidence of RSV infections over time compared to placebo, without an increased incidence of other viral infections. According to the authors, the similar incidences of non-RSV respiratory viruses between the nirsevimab and placebo groups further support the nirsevimab-specific prevention of RSV and suggest no replacement of RSV with other viruses following nirsevimab administration.
Early Administration of Nirsevimab
A separate study published in Morbidity and Mortality Weekly Report by New York City Health Department researchers found 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 encompassed children both eligible and ineligible for Vaccines for Children (VFC).
As per the Advisory Committee on Immunization Practices' recommendations in 2023, nirsevimab should be administered to infants aged 7 months and younger, as well as to infants and children aged 8 to 19 months with risk factors for severe RSV disease, either shortly before the RSV season or within the first week of life if born during October through March in most of the United States. In New York City, 15,521 nirsevimab doses were given to infants and children aged 0 to 19 months 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.
The authors emphasized the importance of an adequate supply of nirsevimab entering the 2024–25 RSV season to ensure continued protection for infants and children.
