A trial of more than 3,000 healthy full-term infants shows clesrovimab, a single-dose monoclonal antibody, reduced the incidence of respiratory syncytial virus (RSV)-associated medically attended lower respiratory infection and RSV-associated hospitalization.
The findings were published last week in The New England Journal of Medicine. The authors said clesrovimab mitigates the risk of viral resistance and reduces the risk of viral escape.
Clesrovimab also has high tissue distribution and concentration in the nasal compartment.
“Clesrovimab also has high tissue distribution and concentration in the nasal compartment,” the authors wrote, which may aid in neutralizing RSV.
The phase 2b/3 CLEVER trial was conducted at 217 sites in 24 countries, and included 2,412 infants who received clesrovimab, and 1,202 infants received placebo. Participants received either a single 105-mg dose of clesrovimab or a placebo and followed through 150 days after injection.
The research was funded by Merck, the maker of the drug. The US Food and Drug Administration (FDA) approved clesrovimab (trade name, Enflonsia) on June 9 for infants entering their first RSV season.
84% effective in preventing hospitalizations
During the 5-month follow up, RSV-associated medically attended lower respiratory infection occurred in 60 of 2,398 infants in the clesrovimab group (incident rate of 2.6%) and in 74 of 1,201 infants in the placebo group (incidence rate of 6.5%).
The efficacy for preventing medically attended RSV infections was 60.4% (95% confidence interval [CI], 44.1% to 71.9%). The injection was 84.2% effective in preventing RSV-related hospitalizations (95% CI, 66.6% to 92.6%). RSV-associated hospitalizations were reported in 9 of 2,398 infants in the clesrovimab group and in 28 of 1,201 infants in the placebo group.
“The observed efficacy of clesrovimab relative to placebo was generally similar across subgroups according to gestational age, body weight, chronological age, and geographic hemisphere and was consistent with the efficacy for the overall population,” the authors wrote.
Participants were also tracked during a second RSV season, and those who had received clesrovimab were at no increased risk of severe of RSV infection in the second RSV season in as compared with the placebo group.
Clesrovimab similar to palivizumab
In a letter published in the same journal, some of the same authors also reported interim results from a phase 3, randomized, partially blinded, palivizumab-controlled trial of clesrovimab (the SMART trial). “The primary objective of the trial was to evaluate the safety of clesrovimab as compared with palivizumab during RSV season 1,” the authors noted.
Palivizumab (brand name, Synagis) made by SOBI, is another monoclonal antibody for preventing RSV. It was approved for RSV in 1998, but will be discontinued this year.
For the SMART study, the incidence of RSV-related lower respiratory infections were similar in the two groups, 3.6% for clesrovimab and 3.0% for palivizumab.
“In infants at increased risk for severe RSV disease, single-dose clesrovimab had results similar to those of monthly palivizumab with respect to the safety profile and incidence of RSV-associated disease,” the authors concluded.