A clinical trial of an mpox vaccine in adolescents found it was safe and generated an antibody response equivalent to that seen in adults.

The interim results of this National Institutes of Health (NIH)-funded trial were presented at the IDWeek2024 conference in Los Angeles.

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Colourised transmission electron micrograph of mpox virus particles (light green) found within VERO E6 cells (teal). The virus particles are in various stages of maturity, which accounts for differences in shape. Captured at the NIAID Integrated Research Facility in Fort Detrick, Maryland.

Two types of the virus that causes mpox have been identified. Clade I is endemic in Central Africa and can cause severe illness. Clade II, endemic in West Africa, caused the global mpox outbreak that began in 2022 and tends to result in milder illness.

A large proportion of people affected in the current Clade I outbreak in the Democratic Republic of the Congo and other African countries are adolescents and children.

The modified vaccinia Ankara-Bavarian Nordic (MVA-BN) vaccine is approved in several countries for the prevention of mpox and smallpox in adults, but insufficient data are available to support licensure for people younger than 18 years.

NIH’s National Institute of Allergy and Infectious Diseases (NIAID) is sponsoring a mid-stage study in the United States to evaluate the safety and immune response generated by two doses of MVA-BN in adolescents aged 12-17 years, comparing outcomes to those in adults aged 18-50 years.

In a planned interim analysis, study investigators measured antibody levels two weeks after the second dose (study day 43) and monitored safety through 180 days after the second dose (study day 210).

The analysis showed that the MVA-BN vaccine generated antibody levels in adolescents equivalent to those observed in adults at day 43 and found that the vaccine was well tolerated through study day 210.

The authors underscored the need to evaluate the MVA-BN vaccine in younger children to extend the evidence base to all people affected by mpox.

Diana Spencer, Senior Digital Content Editor, DDW