Sabin and wild polioviruses from apparently healthy primary school children in northeastern Nigeria.

Despite significant success of the Global Polio Eradication Initiative (GPEI) in Nigeria, Afghanistan, India, Pakistan, wild poliovirus still occurs due to persistently high proportions of under and unimmunized children. The study aimed at determining the type of poliovirus often excreted into the environment. Four hundred nine fecal samples collected from apparently healthy school children aged 5-16 years in Borno and Adamawa States, northeastern Nigeria, were tested for poliovirus by tissue culture technique. The isolates were characterized further by intratypic differentiation testing and genetic sequencing. Three wild poliovirus type, 11 Sabin type, combination of Sabin-types 1 + 2 and 2 + 3 poliovirus, and 22 non-polio enteroviruses were obtained. The continued excretion of wild-type poliovirus among children above 5 years old vaccinated with oral polio vaccine contributes to the persistent circulation of these viruses in the environment and may limit the population immunity. However, the excreted Sabin poliovirus is capable of immunizing the unvaccinated children and promotes herd immunity. Similarly, the excretion of combination of two polio serotypes indicates the child susceptibility to the missing serotype (s) and therefore indicates an immunity gap. The common unhygienic practices in the environment could aid the spread of these viruses through oral-fecal route. Asymptomatic transmission of wild poliovirus among older oral polio vaccine-vaccinated children poses a serious threat to polio eradication program in Nigeria and therefore, environmental and serological surveillance with larger sample size are important for monitoring poliovirus circulation in Nigeria.