Analysis of historical epidemiological data to guide intervention policy in the face of an infectious disease outbreak: poliomyelitis in Israel in 1988.

During the 1988 outbreak of 15 cases of Type 1 poliomyelitis mainly among previously vaccinated young adults in Israel, there were conflicting views on the need for and timing of mass vaccination. Since there was a possibility that the initially localized outbreak may spread more widely, it was felt that an early decision on vaccination policy should be made. Public health officials were faced with varied interpretations of the existing data on the extent of the immune status of the population; some indicating that as many as 15% of young adults lacked immunity to the Type 1 virus. Two major questions posed were whether or not the outbreak was a purely localized event in a single subdistrict, and whether the seasonality of the disease would limit its spread. Based on historical data, probability analysis of three cases occurring outside the subdistrict at the time of the outbreak suggested more widespread dispersion of the virus. Further analysis indicated very limited seasonality of the disease in this region, suggesting that the onset of colder weather would have little impact on the spread of the virus. Careful analysis of the local epidemiology of the disease is an important tool for guiding urgent decisions on mass intervention policy in outbreak situations.