Merck’s investigational antibody clesrovimab demonstrated more than 60% effectiveness in reducing some types of respiratory syncytial virus-associated infections in infants, while Pfizer’s RSV vaccine Abrysvo showed 90% effectiveness at preventing the most severe RSV cases in adults 60 years and older.
At the ongoing IDWeek 2024 Conference in Los Angeles, Merck and Pfizer both presented new data for their respective prophylactic options for respiratory syncytial virus, touting strong protective effectiveness against the infection and related hospitalizations.
Their findings come as the U.S. enters a new respiratory syncytial virus (RSV) season, which typically starts in fall and peaks during winter. According to the National Foundation for Infectious Diseases, RSV is the most common reason for hospitalization in children under 1 year, causing up to 80,000 admissions per year. The virus is also a major source of respiratory morbidity in older adults.
Merck unveiled Phase IIb/III data for its investigational antibody clesrovimab, a single dose of which was administered to healthy preterm and full-term babies entering their first RSV season. The study’s primary efficacy outcome was the percentage of participants with RSV-associated medically attended lower respiratory infection (MALRI), defined as having at least one indicator of LRI or severity. More than 3,600 infants from birth to 1 year of age were enrolled.
Results showed a 60.4% drop in RSV-associated MALRI at 150 days after dosing, compared with placebo. At this time point, clesrovimab also lowered RSV-associated hospitalizations by 84.2% and RSV-associated LRI hospitalizations by 90.9%.
Merck backed these data up with additional analysis from a separate Phase III study, which compared the safety and efficacy of clesrovimab versus palivizumab in infants and children who are at heightened risk of severe disease. Findings demonstrated that rates of RSV-associated MALRI and hospitalizations were similar between treatment arms.
Clesrovimab was also safe and well-tolerated, with no concerning serious toxicity signals and treatment- or RSV-related deaths, according to Merck.
Paula Annunziato, senior vice president of infectious diseases and vaccines clinical research at Merck, in a statement called these findings “clinically meaningful,” which “highlight the potential for clesrovimab to lessen the significant impact RSV can have on infants and their families, as well as the strain on the healthcare system.”
At IDWeek 2024, Pfizer unveiled results from a retrospective analysis of adults 60 years and older who presented to emergency care with severe disease. In the study population, immunization with the company’s vaccine Abrysvo showed 90% effectiveness at preventing the most severe RSV cases, according to Endpoints News.
The retrospective study was conducted by Kaiser Permanente in California but was funded by Pfizer.
These data come after the U.S. Centers for Disease Control and Prevention narrowed its RSV vaccination guidelines for seniors. Per a June 2024 communication, the agency now only recommends RSV shots for all older adults aged 75 and older. In the 60 to 74 age group, vaccination is only recommended for those at risk of severe disease.
This change could have significant implications for the industry, with analysts forecasting a nearly 65% drop in RSV revenues. According to a July 2024 report from Airfinity, sales for RSV shots in the U.S. are now only projected to reach $1.7 billion by 2030, down from a previous estimate of $4.7 billion.
Despite bleaker sales prospects, Pfizer continues to shore up the evidence base for Abrysvo. In addition to results presented at IDWeek 2024, the pharma in August 2024 announced that the vaccine can elicit a strong neutralizing response against the virus in immunocompromised adults.
