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Background: Attenuated vaccinia virus strain, LC16m8, defective in the B5R envelope protein gene, is used as a stockpile smallpox vaccine strain in Japan against bioterrorism: the defect in the B5R gene mainly contributes to its highly attenuated properties., Methods: The protective activity of LC16m8 vaccine against challenge with a lethal dose of vaccinia Western Reserve strain was assessed in wild-type and immunodeficient mice lacking CD4, MHC class I, MHC class II or MHC class I and II antigens., Results: The immunization with LC16m8 induced strong protective activity comparable to that of its parent strain, Lister (Elstree) strain, in wild-type mice from 2 days to 1 year after vaccination, as well as in immunodeficient mice at 2 or 3 weeks after vaccination. These results implicated that the defect in the B5R gene hardly affected the potential activity of LC16m8 to induce innate, cell-mediated and humoral immunity, and that LC16m8 could be effective in immunodeficient patients., Conclusion: LC16m8 with truncated B5 protein has an activity to induce immunity, such as innate immunity and subsequent cell-mediated and humoral immunity almost completely comparable to the activity of its parental strain Lister., (Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The time interval required to develop immunity after vaccination, in the event of a bioterrorist attack using variola virus, is yet to be clarified. In this article, a historical vaccination study conducted in Japan in 1929 was re-examined. Forty-four previously vaccinated and 44 unvaccinated children were involved. After successful first round primary (or re-) vaccination, all children underwent revaccination at variable intervals. Absence of a major reaction (vaccine 'take') after revaccination was taken as a sign of immunity conferred by first round primary (or re-) vaccination. Univariate analysis was employed to examine the relationship between vaccine 'take' and the exposure variables. Maximum likelihood estimates of the time period required to develop immunity were obtained using a simple logit model. The interval between vaccinations was significantly associated with vaccine 'take' in both the previously unvaccinated (p < 0.01) and vaccinated (p < 0.01) groups, and the median interval required for immunity after vaccination was estimated to be 6.4 [95% Confidence Interval (CI): 5.8, 7.1] and 4.3 days (95 % CI: 4.1, 4.7), respectively. Obtained estimates were consistent with previous observations, and the logistic fits reasonably explained the discrepancy among previous suggestions. The findings suggest that it is necessary to vaccinate exposed susceptible individuals within 3 days after exposure to ensure disease protection, and within at least 5 days (for those previously unvaccinated) to provide a certain level of protection; the probability shows a dramatic decline hereafter.

Background: There has been concern that variola virus might be held clandestinely elsewhere. Through constructing mathematical model based on the detailed epidemiologic data, we focused on simulating the various possible scenarios arising from a bioterrorist attack whereby smallpox virus was introduced into Japan, and sought to develop the most effective way of nationwide vaccination policy based on the theory of residual immunity., Method: The analysis is based on a deterministic mathematical model which predicted the epidemiologic outcome while simultaneously evaluating the effect of any specified control strategy of the smallpox epidemic. To clarify the required amount of vaccines, we performed mathematical analysis for hypothetical population to acquire herd immunity based on long-lasting vaccinal immunity., Results: It is demonstrated that the crude size of the potential epidemic could be greatly affected by possible level of residual immunity. The results also suggest the possibility to develop optimal distribution of nationwide vaccination according to the immune status. The prevalence at 50th day among population without immunity in our simulation would be approximately 405 times greater than expected population with residual immunity, and required amount of vaccines for equal distribution would be 3.13 times more than optimal distribution., Conclusion: The mathematical model formulated could determine the vaccination priority based on the real status of immunity which required much less amount of vaccinations than would be calculated using an equal distribution program. It is therefore crucial to determine the real immunity status of the population via epidemiologic studies.

The success of global smallpox eradication in 1980 led all the nations of the world to discontinue smallpox vaccination. To date, however, the threat of deliberate release of smallpox virus has led health authorities to reconsider smallpox vaccination and at the same time, to urge to evaluate duration of the immunity of the population vaccinated before 1980. Although available data is scarce and incomplete, the study suggests that protective immunity lasts longer in a good percentage of vaccinees, although the real percentage and duration are not known. Accordingly, how to establish a national vaccination policy for preparedness in Japan and elsewhere was discussed. The study is intended to cause interest and debate among the medical and public health community.