Paralytic poliomyelitis in the Gaza Strip and West Bank during recent years.

Numerous cases of paralytic poliomyelitis occurred during epidemic years and in interepidemic periods in recent years in the Gaza Strip and the West Bank. During the epidemics of 1974 and 1976, more than 100 paralytic cases were recorded each year. The dominant poliovirus was type 1. In interepidemic years, especially in the Gaza Strip, type 3 poliovirus was the prevalent type. The age group affected were infants and children up to 3 years and 50% of cases occurred during the first 12 months of life. Since 1968, oral poliovirus vaccine has been administered extensively to infants, 2 to 13 months of age. Though vaccine coverage was far from being complete, 3 doses of trivalent oral vaccine were given to the great majority of infants of this age group. Many of the paralytic cases occurred in unvaccinated or incompletely vaccinated (1-2 doses) children. However, numerous cases were recovered in children given three and four feedings. Serologic studies carried out on many of the paralyzed children indicated that "vaccine failures" had occurred. It seems that many of the vaccine failures were due to the massive and widespread circulation of various types of interfering enteroviruses. Laboratory tests of vaccine samples returned from the field prove that the vaccines used were undoubtedly of adequate potency. For these reasons we are planning a program of combined use of oral and inactivated vaccine in order to bypass the interference phenomenon.