Why did routine smallpox vaccination end after smallpox was eradicated?

Routine smallpox vaccination was discontinued because the disease was officially declared eradicated in 1980, eliminating the global threat and the necessity for widespread prevention.12

The eradication campaign was successful because smallpox has no nonhuman reservoir, infected individuals generally become contagious only after symptoms appear, and the disease is easily identified by its characteristic rash. These factors allowed public health officials to effectively interrupt transmission chains.2

With the disappearance of the disease, the incentive for routine vaccination decreased, as the vaccine itself carries risks of side effects—ranging from mild symptoms like fever and headache to severe complications such as myocarditis, brain inflammation, or the spread of the vaccinia virus to others. Today, vaccination is reserved for specific high-risk groups, such as certain laboratory and military personnel, and countries maintain strategic stockpiles to prepare for the potential accidental or deliberate reintroduction of the virus.12