A second dose of Moderna’s mRNA-1345 respiratory syncytial virus vaccine administered approximately 24 months after a primary dose was well tolerated and produced neutralizing antibody responses that met prespecified criteria for noninferiority compared with those after primary vaccination, according to a phase 3 study published in The Journal of Infectious Diseases.
The randomized, observer-blind, placebo-controlled study evaluated revaccination in adults aged 60 years or older. All participants had previously received mRNA-1345 and were randomly assigned in a 2-to-1 ratio to receive another dose of the vaccine or placebo approximately 24 months later. The primary objectives were to assess safety and determine whether neutralizing antibody responses against RSV-A and RSV-B after revaccination were noninferior to those observed after the primary dose.
The study included 1,502 participants who received an injection, including 998 who received mRNA-1345 and 504 who received placebo. Participants were enrolled at 55 sites in the United States.
According to the study, revaccination met the prespecified noninferiority criteria for neutralizing antibody responses against both RSV-A and RSV-B at 29 days. The authors wrote that revaccination “elicited RSV-specific nAb responses that were comparable to those observed after the primary dose.”
The authors also reported that neutralizing antibody levels against RSV-A and RSV-B remained above baseline approximately 24 months after the primary vaccination. Immune responses following revaccination were generally consistent across prespecified demographic and clinical subgroups, including age and the presence of certain comorbidities.
Revaccination was generally well tolerated, according to the study. The most frequently reported solicited reactions included injection-site pain, fatigue, myalgia, headache, arthralgia and chills. Most solicited reactions were mild or moderate, and the authors reported that their incidence was generally similar to that observed after participants’ primary vaccination.
Serious adverse events were infrequent in the 28 days after revaccination and occurred at similar rates in the vaccine and placebo groups. None of the serious adverse events during that period were considered by investigators to be related to the vaccine. The authors said no safety concerns were identified.
The study did not directly evaluate vaccine efficacy following revaccination. The authors identified this as a limitation and noted that no cases of RSV-associated lower respiratory tract disease meeting study criteria occurred in either group during the substudy. The study also included relatively few participants aged 80 years or older.
“In conclusion, this randomized, phase 3 clinical trial demonstrated that revaccination with mRNA-1345 in adults aged ≥60 years administered 24 months after primary vaccination was noninferior to primary vaccination and raised no safety concerns,” the authors wrote.
The study was supported by Moderna Inc. Medical writing and editorial assistance was also funded by Moderna. Some authors are employees of Moderna, Inc., and may hold stock or stock options in the company. The others had no conflicts to disclose.
