Smallpox revaccination of 21000 first responders in Israel: lessons learned

Between July 2002 and April 2003, over 21000 individuals were revaccinated against smallpox by the Israeli Ministry of Health. The objectives of the campaign were to create an immunized core of first responders, to review vaccination techniques, and to produce vaccinia immune globulin (VIG).

The Lister strain of vaccinia virus was used at a concentration of approximately 10(7) pock-forming units (PFU)/ml, and was administered by the multiple-puncture technique. The revaccinees were from varied ethnic backgrounds, almost all were aged 25-64 years, and all participants had been vaccinated against smallpox in the past.

The proportion of clinical take was 66.1% (95% CI: 65.2%, 67.0%), similar to past vaccination programs when take also occurred in approximately two thirds of vaccinees. An antibody response occurred in 77.7% (95% CI: 74.8%, 80.6%) of all revaccinees: 94.4% (95% CI: 91.8%, 96.3%) of those with clinical take and 56.6% (95% CI: 51.3%, 61.8%) of those without clinical take. The most common side effects corresponded to symptoms of non-specific viral diseases, and only a few revaccinees reported serious side effects.

The campaign achieved all its basic goals and provided useful lessons for any mass-vaccination programs that might be necessary in the future.