The Spanish royal philanthropic expedition to bring smallpox vaccination to the New World and Asia in the 19th century.

The New World was ravaged by smallpox for several centuries after the Spanish conquest. Jenner's discovery of the smallpox vaccine made possible the prevention and control of smallpox epidemics. In response to a large outbreak of smallpox in the Spanish colonies, King Charles IV appointed Francisco Xavier de Balmis to lead an expedition that would introduce Jenner's vaccine to these colonies. During the journey, the vaccine was kept viable by passing it from arm to arm in orphaned children, who were brought along expressly for that purpose and remained under the care of the orphanage's director. This expedition was the first large scale mass vaccination of its kind. The historic legacy of this pioneering event in international health should be revisited in the current era of persistent inequalities in global health.