Prevalence of antibodies to Vaccinia virus after smallpox vaccination in Italy.

Decades after smallpox was eradicated and vaccination discontinued, the level of residual immunity in today's population is largely unknown. This study describes an epidemiological assessment in Italians of antibodies against the intracellular mature virus (IMV) and extracellular envelope virus (EEV) forms of Vaccinia virus. Serum samples (n = 642) were taken in 1993 and 2003 from people between 11 and 102 years old. Most citizens >27 years old were positive for antibodies to IMV and EEV. These antibodies were long-lasting and similar titres were present in citizens between 30 and 100 years old. Serum samples from 1993 and 2003 displayed very similar EEV- and IMV-specific antibody titres. By using these data and demographic considerations, it was predicted that, in 2003, 46 % of the Italian population were positive for both IMV and EEV, 42 % were negative for both and 12 % were positive for one antigen.