Issues have arisen recently about the possible use of smallpox for any bioterrorism assault. created before 1969 and 50% of those created between 1969 and 1975 were also found to have managed neutralizing antibodies against smallpox. A considerable proportion of the previous vaccinated individuals still retain significant levels of antiviral immunity. This long-lasting immunity may provide some protecting benefits in the case of reemergence of smallpox, and the disease may not spread as widely and fatally as generally expected. Smallpox was officially declared eradicated from the World Health Corporation in 1980 after a worldwide mass vaccination AZD6244 marketing campaign (22). Program smallpox vaccination was discontinued in Japan in 1976, prior to the declaration. However, issues possess arisen recently about the possible use of variola disease, the causative agent of smallpox, like a bioweapon (14). A total of 37 million Japanese, accounting for approximately 30% of the total population, who have been born after the discontinuation of the routine vaccination program are considered to be completely susceptible to smallpox (1), but the immune status of those who have been vaccinated decades ago is definitely uncertain. It had been believed that the full protecting immunity conferred by smallpox vaccination lasts only 3 to 5 5 years and that even partial immunity fades considerably after 10 to 20 years (5, 14, 21). Recently, however, it has been suggested AZD6244 the immunity may last much longer. Several epidemiological studies have shown that immunity to smallpox may still be present many years after the vaccination (8, 13, 15). The degree of residual safety in vaccinated instances was estimated (8) by analyzing data within the outbreak that occurred in Liverpool, in the United Kingdom, during 1902 to 1903 (13) and on smallpox epidemics AZD6244 that occurred following reintroduction to Europe between 1950 and 1971 (15). The authors concluded that safety against fatal smallpox disease was lost at the rate of 0.363% per year and, thus, that 77.6% of vaccinees were still safeguarded even 70 years after vaccination (8). Furthermore, El-Ad et al. reported the levels of virus-specific neutralizing antibody remain stable for at least 30 years after revaccination (9), and T-cell immunity in response to smallpox vaccination was also reported to remain constant for decades (7, 11). It has recently been shown that B-cell and T-cell-deficient mice immunized with revised vaccinia disease Ankara, an attenuated vaccinia disease, are both safeguarded against challenge having a pathogenic vaccinia disease, although depletion of a single component of the immune response can AZD6244 reduce the degree of safety (17, 24). In contrast, double-knockout mice deficient in major histocompatibility complex class I and II were not protected (24). These findings show that both humoral and cellular immunities make significant contributions to safety against smallpox. With respect to humoral immunities, neutralizing antibodies are believed to play a crucial part in the safety against smallpox (14, 16, 19). Several studies have shown that certain levels of neutralizing antibodies might be involved with preventing the disease or attenuating disease severity (4, 16, 19), even though actual neutralizing antibody titers regarded as sufficient to HSP90AA1 protect against smallpox remain to be identified. These data endorse the idea that adequate serum antibody levels might be one of the benchmarks of protecting immunity. If people who were vaccinated some decades ago still preserve some immunity against smallpox, the morbidity, mortality, and transmission rates associated with the disease might be reduced significantly compared with present objectives (3, 18, 20). This might also impact long term vaccination policy. Therefore, it is important to clarify whether individuals who were vaccinated decades ago maintain any.