A clinical trial by the US National Institutes of Health (NIH) has shown that Bavarian Nordic’s mpox vaccine induced an antibody response in adolescents equivalent to that of adults.

The interim results, presented at the Infectious Diseases Society of America’s IDWeek2024 conference in Los Angeles, could provide backing to aid the vaccine’s extended use in those under 18 years of age in the US and other areas where mpox cases have occurred.

Bavarian Nordic won an European Medicines Agency (EMA) approval for MVA-BN’s use in adolescents in September this year, whilst in the US it is still only approved in adults under the brand name Jynneos. During the 2022–2023 mpox outbreak, though, the FDA did grant the vaccine an emergency use authorisation for both pre- and post-exposure use in adolescents.

The NIH stated that whilst several countries have approved the vaccine for the prevention of mpox and smallpox in adults, there is “insufficient data available to support licensure for people younger than 18 years,” as per a 16 October press release.

The National Institute of Allergy and Infectious Diseases (NIAID)-sponsored Phase II study (NCT05512949) was conducted in the US in individuals aged between 12 and 17 years. After two doses, antibody levels were found to be equivalent at day 43 to those in adults aged 18 to 50 years. The overall frequency of adverse events was comparable between the study groups, with the vaccine well tolerated through day 210 of the study. Dizziness was reported more often in the adolescent group, but the NIH stated this is also seen in many other vaccines given to a younger age group.

The randomised mid-stage study enrolled 229 healthy adolescents, some of whom have a human immunodeficiency virus (HIV) infection. People with compromised immune systems and those who are pregnant are being adversely affected by the Clade II mpox outbreak in Africa, with a large portion of those testing positive in the continent under the age of 18 years old.

Whilst mpox cases have steadily increased in areas of Africa over the past decade, the number of cases reported so far this year has already exceeded last year’s total, with more than 24,000 confirmed or suspected mpox cases because Clade I and Clade II, including over 600 deaths.

Even though the NIH study team says the data supports the safety and quality of the immune response in adolescents, the authors reiterated the need for further evaluation in younger children.

Bavarian Nordic is gearing up for its own Phase II clinical trial (NCT06549530) to assess the immunogenicity and safety of MVA-BN in children between two and 12 years of age. The company has previously said it aims “to further extend the indication of the vaccine into younger populations”. The trial, partially funded by the Coalition for Epidemic Preparedness Innovations (CEPI), is expected to start this month.