Israel Medical Association Journal

Background: During 2013–2014 Israel experienced a continuous circulation of wild poliovirus type 1 (WPV1) but with no clinical cases. WPV1 circulation was gradually terminated following a national vaccination campaign of bivalent oral poliovirus vaccine (bOPV) for 943,587 children < 10 years. Four cases of children with neurological manifestations that appeared following bOPV vaccinations were reported during the campaign: three of Guillain-Barré syndrome (GBS) and one of acute disseminated encephalomyelitis (ADEM). 

Objectives: To present an analysis of these cases, the rapid response and the transparent publication of the results of this analysis. 

Methods: The clinical, laboratory and epidemiological data of these four patients were available during the analysis. In addition, data regarding the incidence of GBS and ADEM during previous years, and reported cases of acute flaccid paralysis (AFP) and the incidence of Campylobacter jejuni enteritis were collected from the Epidemiology Department of the Israel Ministry of Health.

Results: The incidence of GBS among bOPV-vaccinated children was not higher than among bOPV-unvaccinated children. For all the cases reviewed the "incubation period" from vaccination to the event was longer than expected and other more plausible causes for the neurologic manifestations were found. There is no evidence in the literature of a causal relationship between bOPV and ADEM. 

Conclusions: There was no association between the bOPV vaccine and the reported neurological manifestations. We believe that our experience may assist other public health professionals when confronting a similar problem of alleged side effects during a mass medical intervention.

 

Background: Poliovirus rapidly evolves by nucleic acid substitutions and genetic recombination with other polioviruses and non-polio enteroviruses. Evolving oral poliovirus (Sabin strains) can rapidly revert to neurovirulence and undergo antigenic alterations.

Objectives: To evaluate the threat of vaccine-derived poliovirus (1–15% divergence from the respective Sabin strain) for a poliomyelitis-free population in a country with a long-standing routine vaccination program.

Methods: We characterized genetic and antigenic changes in OPV[1] strains isolated from sewage in Israel and evaluated intestinal immunity by measuring fecal excretion after OPV challenge of vaccinated children.

Results: Characterization of poliovirus from sewage revealed eight type 2 and three type 3 vaccine polioviruses that had replicated and started to evolve (vaccine that replicated and diverged by 0.5 to ≤ 1.0%) and nine highly diverged type 2 vaccine-derived polioviruses (1–15% divergence from the respective Sabin strain) with 8–14% divergence between the years 1998 and 2005. Six of the eleven VRPV[2] uniquely recombined with OPV and/or NPEV[3]. The nine VDPV[4] were epidemically related, genotypically neurovirulent, and had 10–15 amino acid substitutions in antigenic sites altering their antigenicity, but shared a single recombination. Type 2 OPV was excreted by 23% and 17% of infants challenged with OPV 3 months after partial immunization (two doses each of OPV and enhanced inactivated poliovirus) or full immunization (three doses of each) respectively, despite high humoral antibody titers.

Conclusions: Our findings, which show that OPV is excreted for a significant period by children with high humoral immunity, emphasize the long-term potential threat from VDPV in highly vaccinated populations. An adequate immunization program, combined with environmental surveillance, is necessary to prevent poliomyelitis and community transmission of poliovirus. 

For children born after 1 January 2005, use of the Sabin oral polio vaccine in combination with the enhanced-potency Salk inactivated polio vaccine as part of the routine vaccination schedule was discontinued. The schedule now includes only IPV [1]. In September 2005, a fifth dose of pertussis vaccine was added for pupils in their second year of elementary school. This article describes the reasons for these changes, which have rendered Israel's routine vaccination program one of the most effective in the world.