this church has an active missionary program with frequent international travel, importation from this source could be an ongoing problem until polio is eradicated worldwide. During a 1979 outbreak, a total of 11 cases of disease were reported from three provinces: Alberta and British Columbia (which used OPV), and Ontario (which used IPV). In 1993, wild-type virus was detected in several families in Alberta after visits to the Netherlands following a Dutch outbreak, but wild-type virus was not detected in small studies in either Ontario or British Columbia. In both of those outbreaks, no disease and no viral spread were detected in the vaccinated communities in or near the areas where Dutch Reformed Church members lived.
From 1965 to 1993, 19 cases of VAPP occurred in Canada; the majority were contact cases, unlike the experience in the United States. Since 1988, all of the polio cases in Canada have been vaccine associated.
Some Canadian provinces have made the decision to change the polio vaccine of primary reliance. The switch has been facilitated by two factors. First, a quadrivalent DTP-IPV vaccine has been available in Canada for more than 20 years; more recently, a pentavalent combination that uses the DTP-IPV vaccine as the diluent for the tetanus toxoid conjugate of the Haemophilus influenzae type b vaccine (Hib) has become available. One of the concerns in this switch has been the issue of immunologic interactions with combination vaccines. Postmarketing surveillance for vaccine failures is ongoing. The second factor facilitating a switch was the ability to introduce IPV as a cost-neutral change to the vaccine program. Although the unit dose is more expensive, the higher wastage rate in Canada of OPV in comparison with IPV (an estimated 50 percent versus 10 percent) made the change cost neutral. Ontario switched from IPV to OPV in 1989 and then back to IPV, the change necessitated by the temporary lack of an IPV supply; implementation of the policy change was relatively easy. The combination product (DTP, IPV, and Hib) is now used in all provinces except Quebec and Manitoba. Quebec has made the decision to switch to the combination product, but Manitoba has not yet made a decision. IPV usage for children in Canada went from about 40 percent in earlier years to more than 70 percent by the end of 1985.
As mentioned earlier, decisions about immunization policy in one part of the world are dependent on the situation internationally. The United States
The material in this section is adapted from a presentation by Stephen Cochi and comments by other workshop speakers or participants.