Modified vaccinia Ankara: potential as an alternative smallpox vaccine.

Despite the declaration of smallpox eradication in 1980, the existence of variola stockpiles and the threat of bioterrorism demand that immunity to smallpox through vaccination be maintained. Although the currently available vaccine was used for the most successful medical intervention ever accomplished, it also is associated with side effects that are difficult to accept in a vaccine for a disease that has not been present for >25 years. Herein, we review alternative approaches to maintaining immunity to smallpox through vaccination with attenuated poxviruses, and we suggest modified vaccinia Ankara (MVA) as a leading candidate for an alternative smallpox vaccine.