Between April and August 1989, the Emirate of Gizan, Saudi Arabia, experienced an outbreak of 11 cases of paralytic poliomyelitis despite high immunization coverage with oral poliovirus vaccine (OPV). The outbreak occurred after a period of two years during which no cases of poliomyelitis had been reported. The outbreak remained localized and no additional poliomyelitis cases were reported from the rest of Saudi Arabia during 1989. A series of studies was initiated to determine reasons for the outbreak.
Cases of paralytic disease were generally young (82% were <2 years of age), all had documented evidence of prior vaccination with OPV, and the vast majority (91%) had received >3 doses of OPV prior to paralysis onset.
Poliovirus type 1 was isolated from 5 (63%) of the 8 patients from whom rectal swabs or stool specimens were collected. Among the 5 poliovirus isolates, wild type 1 polioviruses from three separate origins were distinguished by genomic sequencing. Serologic investigations suggested that poliovirus type 1 had circulated widely in the outbreak area but not in two unaffected control areas of Saudi Arabia. The outbreak investigation did not provide definitive reasons for the outbreak; however, factors such as selected cold chain failures or other factors affecting the immunogenicity of OPV may have contributed. This outbreak, together with other recent outbreaks (Oman), suggest that maintaining poliomyelitis control in this region may be particularly difficult, and that innovative strategies, such as mass campaigns with OPV, and either sequential or simultaneous use of enhanced potency inactivated poliovirus vaccine and OPV, may be required to achieve eradication of polioviruses from the region.
Conclusion: