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Canada Communicable Disease Report
Volume 29  ACS-1015 October 2003 An Advisory Committee Statement (ACS)
POLIOMYELITIS VACCINATION FOR INTERNATIONAL TRAVELLERSAdobe Downloadable
Document Preamble The Committee to Advise on Tropical Medicine and Travel (CATMAT) provides Health Canada with ongoing and timely medical, scientific, and public health advice relating to tropical infectious disease and health risks associated with international travel. Health Canada acknowledges that the advice and recommendations set out in this statement are based upon the best current available scientific knowledge and medical practices, and is disseminating this document for information purposes to both travellers and the medical community caring for travellers. Persons administering or using drugs, vaccines, or other products should also be aware of the contents of the product monograph(s) or other similarly approved standards or instructions for use. Recommendations for use and other information set out herein may differ from that set out in the product monograph(s) or other similarly approved standards or instructions for use by the licensed manufacturer(s). Manufacturers have sought approval and provided evidence as to the safety and efficacy of their products only when used in accordance with the product monographs or other similarly approved standards or instructions for use. The clinical manifestations of poliomyelitis range from subclinical infection to severe neurologic involvement with paralysis and death. Although the ratio of mild infection to severe disease is widely estimated to be 100:1 to 1000:1(1-3), paralysis rates in some well-documented outbreaks have been much higher(4). Polio infection can be caused by any of three antigenic variants: poliovirus types 1, 2 and 3. In nature, most paralytic disease is caused by poliovirus type 1(5). The fecal-oral route is the most common means of transmission(6). In 1988, the World Health Organization (WHO) targeted poliovirus for control by the year 2000(7) . This was very nearly achieved. The 1990s witnessed an enormous effort to reach the WHO goal, with dramatic increases in national immunization days(8,9) and a marked decline in the number of reported cases worldwide(9). In Canada, the last major epidemic occurred in 1959, when 1887 paralytic cases were reported(10). Following the introduction of the inactivated polio vaccine (IPV) in 1955 and the oral polio vaccine (OPV) in 1962, indigenous transmission in Canada was rapidly controlled(11). The Americas were declared to be free of indigenous polio in 1994(12), and large areas of Eurasia, the Mediterranean, and Micronesia have achieved 100% reporting for acute flaccid paralysis and virtual elimination of wild-type disease(9). Transmission of natural polio continues at a slowed rate in most sub-Saharan African countries and in areas of South Asia and the Orient(13,14). (Information regarding recent and ongoing polio outbreaks can be found at the WHO Weekly Epidemiologic Record Web site - http://www.who.int/wer.) Introduction of wild-type virus from these regions accounts for the small outbreaks in unvaccinated or under-vaccinated populations in regions with otherwise high vaccine coverage (e.g. religious communities)(10,15). To date, there has been reassuringly little evidence of transmission to neighbouring communities when such outbreaks have occurred. Despite the interruption of wild-type virus circulation in the developed world through the 1980s and 1990s, a few cases of polio-associated flaccid paralysis continued to occur (e.g. 10 in Canada between the years 1980 and 1992)(9,16). Virtually all of these cases were attributable to vaccine-strain poliovirus, and the capacity of the Sabin vaccine-strain viruses to revert to neurovirulence was recognized (resulting in vaccine-associated paralytic polio or VAPP)(6,9). Vaccine-strain viruses that revert have the capacity to spread from person to person(17) and to persist for variable periods of time in sewage water(6,9,18). As a result, about 66% of cases of VAPP occur in the close contacts of vaccinees(9). In the mid- to late-1990s, most countries in the developed world and many newly industrialized countries switched from OPV to IPV for national immunization programs(19-21). However, OPV remains a licensed product in all developed countries (including Canada), and a small number of physicians persist in its use despite national recommendations. According to the WHO(22), OPV remains the vaccine of choice in the developing world where vaccine coverage is suboptimal, precisely because of its capacity to spread and to "immunize" unvaccinated individuals. Of particular note for travelling Canadians was a modest outbreak of 21 cases of VAPP on the island of Hispaniola in 2000, in which 13 cases were confirmed in the Dominican Republic and 8 in Haiti. This outbreak was the first in the Americas since 1991. It occurred in areas of very low OPV coverage and was thought to result from the establishment of vaccine-strain virus in the waste water system and inadequate separation of waste and drinking water in that country(23-25). In 2002, as part of enhanced global polio surveillance, three cases of VAPP were confirmed in the Philippines(26). All three cases came from different geographic areas within the Philippines and had never travelled outside their province of residence since birth. Low routine OPV vaccination coverage was blamed for these cases. Wild polio was last reported in the Philippines in 1993. Although such outbreaks have occurred only rarely, the potential for revertant vaccine-strain virus to establish itself in "nature" has had major health consequences. The presence of vaccine-strain virus in waste water is readily demonstrated(27,28) and reinforces the need to maintain high routine coverage in polio-free countries and ensure that travellers have received polio vaccination according to national recommendations. The durability of immunity after polio vaccination (and natural infection) in the complete absence of boosting by either natural infection or exposure to vaccine-strain OPV is largely unknown but is unlikely to be lifelong(9). Although the laboratory correlates of immunity against poliovirus are not completely understood, neutralizing antibodies are believed to be very important in preventing paralytic disease, and the presence of detectable antibodies in the serum is highly correlated with protection(6,9,29). Serosurveys in countries in the developed world suggest that anti-polio antibodies decline with time, such that 5% to 15% of individuals adequately vaccinated in childhood are seronegative by young adulthood(9,30-32). In a serosurvey of 233 U.S. international travellers, about 12% were found to be lacking antibodies to poliovirus types 1 or 3(33). All had antibodies to poliovirus type 2. Travellers who had received polio vaccine within the previous 5 years had detectable antibodies against all three types, but only 84% of those who had not received such a booster had similar protective antibody levels(34). Since wild-type viruses no longer circulate in the Americas(35,36), routine booster doses for adults are no longer recommended for Canadians except under unusual circumstances. One such circumstance is international travel to one of the steadily shrinking regions of the world with epidemic or endemic polio virus activity(14,36) or travel during an outbreak of VAPP(25,26). The risk of exposure to neurovirulent poliovirus (either wild type or revertant vaccine-strain virus) during travel in the developing world is complicated to assess. Factors that influence this risk include geographic considerations (e.g. local epidemiologic patterns of wild-type disease, local use of OPV), infrastructure issues (i.e. the reliability of waste and drinking water management), the duration of travel, exposure to unsafe water or foods prepared in an unhygienic manner, contact with local populations (e.g. aid workers, refugee camps, orphanages), and the style of travel (e.g. back-packing versus resort hotels). In a recent telephone survey of almost 1000 Canadian travellers, as many as 15% reported at least one contact with "sewage" while abroad (Dr. G. De Serres, medical epidemiologist, Quebec Public Health Institute: personal communication, 2003). Recommendations for Travellers Unvaccinated Children Independent of any travel plans, a primary series of immunization with IPV should be undertaken in these children according to the schedules recommended by the National Advisory Committee on Immunization. For infants, this schedule includes at least three and as many as five doses of vaccine (usually at 2, 4, 6, and 12 to 18 months with a booster at 4 to 6 years of age). Only three of these doses (the first, second, and fourth) are thought to be necessary to elicit long-term immunity. (A III) Unimmunized children > 2 years of age can receive a primary series of three immunizations with an interval of 6 to 8 weeks between the first two doses and 6 to 12 months between the second and third doses. (A III) Although the circumstance should arise only rarely, parents of newborns or unvaccinated children < 2 years of age travelling to areas with high polio risk should consider following a more accelerated schedule (e.g. three doses with only 4 to 6 weeks between each dose). (A III) Unvaccinated Adults Independent of travel plans, a primary series of three immunizations with IPV should be considered for all unimmunized adults as recommended by the National Advisory Committee on Immunization (first visit, 2 months later, and 6 to 12 months later). (A III) The requirement for periodic booster doses with IPV in an era without periodic wild-type exposure and boosting is currently unknown. A single dose of IPV in adulthood is simple to administer, for example, in association with an adult dose of diphtheria and tetanus toxoids (dT-IPV), and may provide an extra margin of protection for Canadian travellers regardless of their destination. (C III) Adults with No Proof of Vaccination High vaccine coverage rates for polio were not achieved in Canada until the 1970s. As a result, some Canadians aged > 30 years have incomplete immunity based upon natural exposures and (possible) ad hoc vaccinations. The risk of exposure to wild-type polio for most travellers is too low at the current time to recommend serologic screening of these individuals, and a single booster with IPV is recommended. (C III) Serologic testing to confirm immune status can be considered for adults whose travel plans will put them at very high risk (e.g. refugee or missionary workers in endemic or epidemic areas). Those without a history of vaccination who are found to be seronegative for one or more serotypes should receive a primary series of IPV as already described. (A II) Previously Vaccinated Children (up to date) No additional doses of IPV are recommended for travelling children whose immunizations are up to date. Consideration should be given to securing IPV for the routine immunization of Canadian children who will be abroad for prolonged periods of time (e.g. children of expatriates, missionaries, long-term travellers). A scheduled polio vaccination should not be significantly delayed because of unreasonable fears of VAPP, however, and OPV can be substituted for any of the scheduled doses of IPV without incurring great risk. This is particularly true if the child has already received one or more doses of IPV and the parents are appropriately vaccinated. (A II) As already noted, it may be appropriate to accelerate the routine schedule of vaccination for children whose departure is imminent. Previously Vaccinated Adults A single booster dose of IPV can be considered for adult travellers in South and Central America who will have extensive contact with infants in countries where OPV is still in use. (B III) No booster dose of IPV is currently recommended for routine travel within the Americas or large areas of the developed world (Europe, Mediterranean, Japan, Australia, New Zealand). (E II) A single booster dose of IPV should be offered to international travellers who plan to visit regions of the world where wild-type poliovirus continues to circulate in either epidemic or endemic fashion. A similar argument can be made for a single booster of IPV for travellers who plan to visit regions with documented outbreaks of VAPP. The strength of these recommendations varies with the factors influencing the risk of exposure. (A-C II) Pregnant and Lactating Women There are no absolute contraindications to the use of IPV in susceptible women who are either pregnant or lactating. However, like all immunizations, deferral of IPV vaccination until after delivery should be considered unless the risks of exposure are significant. References
APPENDIX Categories for the strength of each recommendation
Categories for the quality of evidence on which recommendations are made
* From: Macpherson DW. Evidence-based medicine. CCDR 1994;20:145-47.
[Canada Communicable Disease Report]
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