Immune response to an intercalated enhanced inactivated polio vaccine - Oral polio vaccine programme in Israel: Impact on the control of poliomyelitis

A combined enhanced inactivated polio vaccine (EIPV) and oral polio vaccine (OPV) programme was introduced in Israel in 1990, with the purpose of providing a solution to the persistent polio morbidity bz spite of a 30 year long OPV programme. The schedule comprised two noses of EIPV administered at the age of 2 and 4 months, intercalated with two doses of OPV at 4 and 6 months, followed by a reinforcing dose with the two vaccines simultaneously administered at 12 months. The 5-year evaluation of the programme included: the assessment of clinical suspicions 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 sewage specimens collected in25 permanent sites throughout Israel as well as front the Palestinian Authority. No paralytic polio cases associated with a wild or vaccinal poliovirus strain were defected since the introduction of the programme. At the age of 4 months, one week after administration of the second EIPV and first OPV nose, 100% seropositivity 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 seropositivity occurred between the age of 6 and 12 months. Thirty days after the IPV and OPV reinforcing noses, GMTs to each of the foul. poliovirus 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 three vaccinal and the wild poliovirus strain levelled off at rather high values, considered protective. Between 1990 and 1995, 16 wild poliovirus type 1 strains were isolated in three separate episodes in Gaza Strip sewage and once only in one Israeli site very close to Gaza City. The rapidly established high and persistent NA titre to the vaccinal and wild poliovirus strains and the presence of immunological memory are indicative of high individual protection throughout the first 5 years of life. The only one-time introduction, without circulation, of a wild poliovirus strain in a single Israeli settlement suggests community protection. The intercalated programme offers a contribution to polio el eradication by providing a solution to the primary and secondary failure associated with OPV, as well as to the control of vaccine-associated paralytic poliomyelitis. (C) 1998 Elsevier Science Ltd. All rights reserved.