IMMUNE-RESPONSE TO AN INTERCALATED ENHANCED INACTIVATED POLIO VACCINE- ORAL POLIO VACCINE PROGRAM IN ISRAEL - IMPACT ON THE CONTROL OF POLIOMYELITIS

A combined enhanced inactivated polio vaccine (EIPV) and oral polio va ccine (OPV) programme was introduced in Israel in 1990, with the purpo se of providing a solution to the persistent polio morbidity bz spite of a 30 year long OPV programme. The schedule comprised two noses of E IPV administered at the age of 2 and 4 months, intercalated with two d oses of OPV at 4 and 6 months, followed by a reinforcing dose with the two vaccines simultaneously administered at 12 months. The 5-year eva luation of the programme included: the assessment of clinical suspicio ns of polio, early immune response in successive cohorts administered the new schedule, dynamics of the immune profile in a cohort followed rip to the age of 5 and monitoring of wild poliovirus excretion in sew age specimens collected in25 permanent sites throughout Israel as well as front the Palestinian Authority. No paralytic polio cases associat ed with a wild or vaccinal poliovirus strain were defected since the i ntroduction of the programme. At the age of 4 months, one week after a dministration of the second EIPV and first OPV nose, 100% seropositivi ty and high geometric mean titres (GMTs) of neutralizing antibody (NA) to the three vaccinal and to the wild poliovirus type I, responsible for the 1988 polio outbreak, were observed. No change in percent of se ropositivity occurred between the age of 6 and 12 months. Thirty days after the IPV and OPV reinforcing noses, GMTs to each of the foul. pol iovirus strains were greater than or equal to 3037. Up to the age of 5 , the seropositivity was unchanged. After a 2.5-10-fold decline in the first year following the completion of the programme, GMTs to the thr ee vaccinal and the wild poliovirus strain levelled off at rather high values, considered protective. Between 1990 and 1995, 16 wild poliovi rus type 1 strains were isolated in three separate episodes in Gaza St rip sewage and once only in one Israeli site very close to Gaza City. The rapidly established high and persistent NA titre to the vaccinal a nd wild poliovirus strains and the presence of immunological memory ar e indicative of high individual protection throughout the first 5 year s of life. The only one-time introduction, without circulation, of a w ild poliovirus strain in a single Israeli settlement suggests communit y protection. The intercalated programme offers a contribution to poli o el eradication by providing a solution to the primary and secondary failure associated with OPV, as well as to the control of vaccine-asso ciated paralytic poliomyelitis. (C) 1998 Elsevier Science Ltd. All rig hts reserved.