Vaccine, Vol. 15, No. 10, pp. 1123-1129, 1997 0 1997 Elsevier Science Ltd. All riohts reserved zyxwvut PII: S02f3-410X(97)00001-7 e ~~~ ~~ Printed in Great Britain 0264-410X/97 $17+0.00 zyxwvutsr Influence of host related factors on the antibody response to trivalent oral polio vaccine in Tunisian infants H. Triki*ll, M.V. Ould Mohamed Abdallah*, R. Ben Aissa*, A. Bouratbine*, M. Ben Ali Kacemj-, S. Bouraouil_, C. Koubaal, S. Zouaril, E. MohsniT[, R. Crainicg and K. Dellagi* zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA The low eficiency of trivalent oral polio vaccine (TOPV) in inducing zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPON protective antibody titres to polio3 is a problem of great importance in many regions of the world. A prospective study was conducted in 121 Tunisian infants aged 3 months during routine immunization with TOPV under carefully controlled conditions. Seroconversion rates to poliol, polio2 and polio3, one month after the third dose, were 94.7, 100 and 89.5%, respectively. The kinetics of the antibody response showed delayed and more dtjicult responses to polio3 compared to polio2 and poliol. The following host related factors, previously suggested to interfere with the immune response, were assessed: maternal antibodies; breast-feeding; concurrent enteric infections; and other illnesses. The main factor associated with the lack of seroconversion was concurrent infection with non-polio enteroviruses (NPE) which was-found in 50% of non-responders to polio1 andlor to polio3 during the vaccination protocol whereas no NPE was isolated in vaccine responders. The other studiedfactors seemed not to interfere in the infants according to the locally adopted vaccination schedule and to the spectfic socio-economic conditions. 0 1997 Elsevier Science Ltd. Keywords: poliovirus; immunization; antibodies Extensive use of trivalent oral polio vaccine (TOPV) has led to a substantial reduction in the incidence of para- lytic poliomyelitis in many regions of the world. How- ever, since the 1970s the efficiency of this vaccine in inducing humoral immunity against polioviruses types 1 and 3 has been lower than expected in many countries of the developing world’-“. Although rates of seroconver- sion approach 100% in industrialized countries, only 73% (range 3699%) and 70% (range 40-99%) of vacci- nated children in developing countries have detectable antibodies to polioviruses types 1 and 3, respectively”. Several studies showed that vaccine failures could not be explained by breaks in the cold chain nor a sub- optimum vaccine potency6.14,16.17. This situation may contribute to a continuous circulation of wild viruses even in vaccinated children and to the emergence of paralytic disease outbreaks. In fact, recent outbreaks in *Institut Pasteur de Tunis, zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA WHO Regional Reference Laboratory on Poliomyelitis, Place Pasteur, BP 74, 1002, Tunis, Belvedere, Tunisia. tCentre de Protection Maternelle et Infantile Ezzouhour, Tunis, Tunisia. fCentre de Protection Maternelle et Infantile Mellassine, Tunis, Tunisia. TDirection des Soins de Sante de Base, Tunis, Tunisia. §Unite de Virologie Medicale, lnstitut Pasteur, Paris, France. IlTo whom correspondence should be addressed. (Received 7 June 1996; revised 3 December 1996; accepted 6 December 1996) vaccinated sp opulations have already been reported- Gambia16,’ , 0mani4, Brazil”,“, Taiwan”, Senega12’, China21, Finland22 and Israe123. The low efficiency of TOPV may constitute a barrier for the World Health Organization’s (WHO) initiative to eradicate poliomyelitis globally by the year 2000. Although the TOPV low efficiency has been reported for many years, the problem still remains unsolved with reasons not yet clearly understood. Previous studies have suggested that this lack of efficiency could be due to several factors: vaccine potency, formulation and stab- ility; vaccine administration and scheduling; host and environmental factors like interference from breast milk antibodies; concurrent enteric infections; and nutritional status12,15*‘626. However, the aetiologies may differ from region to region depending on local particularities such as the socio-economic development level, the prevalence of enteric infections, etc. A prior retrospective study was conducted in 1990 to estimate the immunogenicity of TOPV in vaccinated children in Tunisia. In spite of high levels of TOPV coverage, low seroprevalences of specific antibodies have been found especially against poliovirus type 327. We report here the results of a prospective study we con- ducted to estimate the clinical efficiency of TOPV in Tunisia in carefully controlled conditions of vaccine quality and administration. The objective was to assess Vaccine 1997 Volume 15 Number 10 1123