Smallpox vaccines: New formulations and revised strategies for vaccination.

Smallpox has been eradicated but stockpiles of the causative infectious agent, variola virus, have been maintained over decades. Today, the threat of accidental or intentional poxvirus release is accompanied by the fact that the existing licensed smallpox vaccines cause rare but severe adverse reactions yet are the only products with approved efficacy against smallpox. New safer vaccines and new strategies of immunization are to be developed to fit to a scenario of emergency smallpox vaccination. However, we still lack knowledge about the pathogen and the mechanisms involved in acquiring protective immunity. Here, we review the history of smallpox vaccines and recent achievements in the development of highly efficacious and safer vaccines and vaccine applications. These include i) assessment of adequate animal models to study pathogenesis and protective immunity, ii) characterization of the immunity elicited by next generation vaccines, and (iii) the investigation of the requirements for rapidly protective vaccination.