are particularly distrustful of vaccines, a participant cited an Oregon study indicating that people who decline vaccination are more affluent and better educated then those who receive vaccine.
Vaccination programs as a whole sometimes have a credibility problem, and vaccine-associated cases of polio jeopardize that credibility in the eyes of some segments of the population. A change to a more acceptable vaccine could help the overall program in terms of completing high rates of coverage for the U.S. population.
The final option presented was to discontinue vaccination against poliomyelitis. The risk of importation is the key factor driving continued vaccination despite eradication from a particular geographic area. Important elements are the ability to detect importations and the nature of who imports the disease.
A comparison was made with smallpox. Vaccination against smallpox ended in the United States in 1971, 22 years after the last case of indigenous disease in this country but before worldwide eradication.
The ability to detect importations is one consideration in the decision to stop vaccination. Because smallpox was a highly visible disease largely without subclinical manifestations, it is fairly certain that any imported cases discovered before eradication were indeed the only cases to have occurred. In contrast, poliomyelitis infection often occurs asymptomatically, so that there is the possibility of undetected importations beyond those that have been documented.
Thus, the likelihood of importations becomes important. At the time of cessation of smallpox vaccination in the United States, the Americas were free of smallpox; cases were still being reported in eastern Africa and south Asia, however. The current situation with polio is similar; poliomyelitis disease occurs in Africa and central Asia. The incidence of the two diseases in comparable periods is similar as well.
Looking at who transmits disease is also important. With smallpox, it was relatively easy to identify who carried the disease from place to place. They tended to be young adults, usually male, who moved within and between countries. Polio epidemiology is such that virtually all of those excreting virus are under 5 years of age and are less likely to travel. On the other hand, more
The material in this section is adapted from a presentation by D. A. Henderson and comments by other workshop speakers or participants.