A recent NIH-funded clinical trial has demonstrated that the modified vaccinia Ankara-Bavarian Nordic (MVA-BN) mpox vaccine is safe and elicits a robust immune response in adolescents aged 12-17 years. The interim results, presented at the IDWeek 2024 conference, suggest that the vaccine could be a valuable tool in controlling mpox outbreaks, particularly in vulnerable populations.
The study, a mid-stage trial conducted across multiple sites in the United States, evaluated the safety and immunogenicity of two doses of the MVA-BN vaccine in adolescents compared to adults aged 18-50 years. Participants received two subcutaneous doses of the vaccine 28 days apart. Researchers measured antibody levels two weeks after the second dose (day 43) and monitored safety through 180 days after the second dose (day 210).
Robust Antibody Response in Adolescents
The interim analysis revealed that adolescents who received the MVA-BN vaccine developed antibody levels equivalent to or higher than those observed in adults. Specifically, geometric mean titers (GMT) in adolescents were 470.3 (95% CI 422.3-523.8), significantly higher than the GMT of 293.2 (95% CI 249.8-344.2) in adults. This translates to a geometric mean titer ratio (GMTR) of 1.60 (95% CI 1.32-1.95), indicating a stronger immune response in the adolescent group.
C. Mary Healy, MD of Baylor College of Medicine in Houston, noted the relevance of these findings, particularly for adolescents in the U.S. and regions affected by ongoing mpox outbreaks, such as the Democratic Republic of Congo (DRC).
Safety and Tolerability
The MVA-BN vaccine was generally well-tolerated in both adolescents and adults. The overall frequency of adverse events was comparable between the two groups. While dizziness was reported more frequently in adolescents (3%) compared to adults (0%), it did not lead to syncope, require medical intervention, or result in discontinuation of the vaccine.
Local reactions, such as pain, erythema, induration, and pruritus, were more common after the second dose in both groups, affecting approximately 80% to 90% of participants. Solicited systemic reactions, including fatigue, headache, and myalgia, occurred at similar frequencies in adolescents and adults for each vaccine dose.
Implications for Public Health
These findings have significant implications for public health, particularly in light of the ongoing mpox outbreaks. The MVA-BN vaccine, already approved for adults, now has strong evidence supporting its use in adolescents. An FDA-approved mpox vaccine for adolescents addresses an unmet public health need, as currently the MVA-BN vaccine is only available in the U.S. under emergency use authorization (EUA) as post-exposure prophylaxis for adolescents younger than 18 years of age considered at high-risk for mpox.
The European Medicines Agency (EMA) has also recommended extending the indication for Imvanex, another name for the MVA-BN vaccine, to include adolescents aged 12-17 years. This recommendation was based on a study comparing the immune response in 315 adolescents to 211 adults, which showed similar responses and safety profiles.
The Need for Further Research
While these results are promising, researchers emphasize the need for further studies to evaluate the MVA-BN vaccine in younger children. "Evaluations in younger children are really urgently needed to extend protection to those who are most vulnerable, particularly in the DRC," said Dr. Healy. Expanding the evidence base to include all age groups affected by mpox is crucial for comprehensive disease control and prevention efforts.
