Academic journal article Bulletin of the World Health Organization

A Developing Country Perspective on Vaccine-Associated Paralytic Poliomyelitis

Academic journal article Bulletin of the World Health Organization

A Developing Country Perspective on Vaccine-Associated Paralytic Poliomyelitis

Article excerpt

Introduction

"From a humanitarian perspective, eradication provides the ultimate in health equity and social justice, bringing identical and universal benefits to every person globally" (1). This article examines how identical and universal these benefits have been. Industrialized countries used either the inactivated poliovirus vaccine (IPV) or the oral poliovirus vaccine (OPV), alone or in sequence, in routine immunization, and thereby rapidly controlled or even eliminated poliomyelitis caused by wild polioviruses (2-4).

WHO advocated OPV exclusively for developing countries both in the Expanded Programme on Immunization (EPI established in 1974) and for polio eradication (from 1988) (5). The five promised advantages of OPV were low cost; ease of administration; high vaccine efficacy for low number of doses; mucosal immunity to stop virus transmission; and vaccine-related virus spread contributing to "contact immunization" (1, 5-7). Accumulated experience and evidence question the reality or impact of some of the putative advantages of OPV (8-11). Consequently, eradication has been an uphill task in developing countries, necessitating nearly 100% OPV coverage with 10-15 doses per preschool child, given in EPI activities and through supplementary immunization campaigns (7).

The incidence of vaccine-associated paralytic poliomyelitis (VAPP) was considered low enough to qualify OPV as "one of the safest vaccines in current use" by WHO (12, 13). In the pre-EPI era, 600 000-800 000 cases of polio occurred annually, the vast majority in developing countries. Many experts accepted VAPP as a price for the greater benefit of controlling wild poliovirus using OPV. The countries themselves, however, had no opportunity to make an informed choice between vaccines. While progress is made towards eradication, VAPP is now becoming more frequent than polio attributable to wild poliovirus infection (14-16). How many VAPP cases, if any, are acceptable in developing countries? Will continued occurrence of VAPP jeopardize the very success of eradication? Will options to eliminate VAPP be affordable? These are essential questions to be solved from a developing country perspective.

The risk and burden of VAPP in developing countries

Clinically, VAPP is indistinguishable from polio caused by wild poliovirus, with an identical incubation period, range of severity and case-fatality rate (12-21). In surveillance fur eradication, poliovirus isolates from children with acute flaccid paralysis (AFP) are characterized as wild or vaccine-derived by reliable laboratory techniques. Identification of wild virus confirms "polio" but all other cases including VAPP are classified as "non-polio" (14, 15). Finding vaccine-derived virus in cases of AFP does not prove VAPP, as it may be a mere passenger infection. Applying specific diagnostic criteria, there were 139 cases of VAPP in Latin America in 1989-91 and 181 cases in India in 1999 (14, 15). Assuming all annual average of 45 cases in Latin America, the total in Latin America and India is 226 cases a year. Thus the annual global burden of 120 cases of VAPP expected by the WHO Technical Consultative Group (TCG) for Poliomyelitis Eradication is a gross underestimate (12). A realistic estimate could be as high as 400-800 (16).

WHO determined the annual incidence of VAPP in European countries to be 0.4-3.0 per million vaccinated children and documented intercountry variations in its frequency (12,13). Disease surveillance to detect VAPP was recommended in countries using OPV, but was not included in the EPI (12, 13). Thus the risk of VAPP remained unnoticed in developing countries. Geographical variation in the risk of VAPP has been confirmed in all subsequent studies (2-4, 14-16, 18, 19). Prior to the introduction of immunization, polio incidence showed considerable geographical variation, and its determining factors may also apply to VAPP (16). In India, the annual incidence of polio in the 1970s and 1980s was 20-40 per 100 000 population (or 2 cases per 1000 children under five years of age), one of the highest in the world (22-25). …

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