Analysis of a previous smallpox vaccination study: estimation of the time period required to acquire vaccine-induced immunity as assessed by revaccination.

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.

Smallpox: clinical highlights and considerations for vaccination.

Smallpox virus has gained considerable attention as a potential bioterrorism agent. Recommendations for smallpox (vaccinia) vaccination presume a low risk for use of smallpox as a terrorist biological agent and vaccination is currently recommended for selected groups of individuals such as health care workers, public health authorities, and emergency/rescue workers, among others. Information about adverse reactions to the smallpox vaccine is based upon studies completed during the 1950s and 1960s. The prevalence of various diseases has changed over the last four decades and new disease entities have been described during this period. The smallpox vaccination may be contra-indicated in many of these conditions. This has made pre-screening of potential vaccines necessary. It is believed that at present, the risks of vaccine-associated complications far outweigh the potential benefits of vaccination in the general population.

Los virus de la viruela y de la vaccinia / The pock virus and of the vaccinia virus

La eliminación mundial del virus de la viruela con el virus de la vaccinia fue un proceso que duró poco más de siglo y medio, que se desarrolló en varias etapas según la aceptación del procedimiento, de los adelantos técnicos y del esfuerzo colaborativo de las autoridades internacionales de salud con los representantes en cada uno de los países del mundo. El virus de la vaccinia es asimétrico y está recubierto por una membrana obtenida cuando el virus maduro sale de la célula infectada. Tiene la forma de un ladrillo y es muy resistente a los efectos de los inactivadores físicos y químicos. La certificación definitiva de la erradicación mundial de la viruela fue hecha por la Asamblea Mundial de la Salud en mayo de 1980; con esto el virus de la vaccinia parecía también haber quedado condenado a la extinción. Sin embargo, la comunidad científica se volvió a fijar en él a consecuencia del desarrollo de la tecnología del DNA recombinante, cuando surgió la posibilidad de romper la barrera genética de los organismos y se logró la recombinación de genomas de cualquier especie. Si el agente infeccioso no es patogénico y el gene proviene de otro agente que si lo es, entonces ese vector de expresión se puede utilizar con una vacuna prácticamente ideal, ya que puede inmunizar al sujeto contra ese patógeno, sin peligro para la salud. Uno de los más lógicos candidatos a servir como vector fue el virus de la vaccinia, debido a que sus cualidades inmunogénicas y de seguridad son excelentes ya que su genoma puede incorporar una cantidad importante de DNA, por lo menos 25,000 pares de bases, sin por ello perder su inefectividad. El virus de la vaccinia cuenta ahora con enormes posibilidades para continuarse usando, ya no como medida profiláctica, específica o no, sino como un vehículo seguro y eficiente de material genético de otros agentes infecciosos