Why did countries store smallpox vaccines after the disease was eradicated?

Following the global eradication of smallpox in 1980, routine vaccination programs were discontinued because the disease was no longer considered a natural threat. However, countries began to produce and store fresh stocks of smallpox vaccine at the beginning of the 21st century due to heightened security concerns.12

These stockpiles serve as a critical measure for emergency preparedness against the potential accidental or deliberate reintroduction of the virus. This concern arose largely because stocks of variola major—the virus that causes smallpox—were maintained in laboratory facilities in the United States and Russia following the disease's eradication. Furthermore, the increasing sophistication of international terrorist groups raised fears that populations could be vulnerable to a deliberate infestation, prompting many nations to ensure they have the capacity to respond rapidly to a potential public health emergency.213