Causality assessment of serious neurologic adverse events following the bOPV national vaccination campaign in Israel

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.