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Positive Results Reported for Respiratory Vaccine
A respiratory syncytial virus (RSV) F-protein recombinant nanoparticle vaccine candidate (Novavax, Inc.) has met all of the primary, secondary, and exploratory objectives of a new midstage clinical trial.
The randomized, observer-blinded, placebo-controlled study involved 1,600 older adults (60 years of age and older) in the U.S. The study was designed to examine prospectively the incidence of all symptomatic respiratory illnesses associated with RSV among community-living older adults who were treated with placebo. The trial also evaluated the safety and immunogenicity of an unadjuvanted 135-mcg dose of the RSV F vaccine compared with that of placebo. Moreover, the trial estimated the efficacy of the RSV F vaccine in reducing the incidence of respiratory illness due to RSV.
The trial is the first to demonstrate the efficacy of an active RSV immunization in a clinical trial population. Vaccine developers have been frustrated in this regard ever since RSV was identified nearly 60 years ago. MedImmune developed palivizumab (Synagis), which also targets the RSV F-protein, but the drug prevents only lung infections caused by RSV, not the RSV infection itself.
The new study showed statistically significant vaccine efficacy in the prevention of all symptomatic RSV disease (44%) and of RSV disease with symptoms of lower respiratory tract (LRT) infection (46%) in older adults. According to Novavax, the observed efficacy was similar to or better than recent effectiveness estimates for several licensed respiratory vaccines tested in older adults, including pneumococcal and standard-dose seasonal influenza.
The study also established an attack rate for symptomatic RSV disease of 4.9% in older adults, 95% of which included LRT symptoms. In addition, the rate of statistically significant efficacy against more-severe RSV illness, as defined by the presence of multiple LRT symptoms associated with difficulty breathing, was 64% in several ad hoc analyses.
Anti-F immunoglobulin G (IgG) and palivizumab-competing antibody (PCA) titers peaked rapidly at day 14, plateaued at day 28, and remained at elevated levels through day 56 (the last time-point analyzed). Greater than four-fold increases occurred in both anti-F IgG and PCA concentrations at days 14, 28, and 56, and serologic responses were achieved in more than 90% of vaccinated subjects, indicating an effective immune response.
Armed with these data, Novavax plans to initiate a phase III study of its RSV F vaccine in 8,000 to 10,000 patients later this year, coinciding with the RSV season in the U.S. Meanwhile, the company is also immunizing pregnant women in a separate midstage trial in an attempt to jumpstart infant immunity.
RSV is a major respiratory pathogen in infants, children, and adults. RSV infections in adults represent re-infections and are generally mild to moderate in severity, except in persons with high-risk conditions, including the elderly and adults with underlying chronic cardiac or pulmonary disease. It is estimated that 2.4 million adults 65 years of age or older are infected with RSV annually in the U.S., leading to as many as 900,000 medical interventions and 14,000 deaths each year. No FDA-approved RSV vaccines are currently available.
Sources: Novavax, Inc.; August 10, 2015; and Reuters; August 10, 2015.