Abstract:
One of the key tools in the fight against polio has been the live, attenuated oral poliovirus vaccine (OPV. Although OPV may require multiple doses to establish immunity, it ultimately offers long-term protection against paralytic disease through lasting humoral immunity. In rare instances, vaccine-associated paralytic poliomyelitis can occur in immunologically normal recipients of OPV, their contacts, or individuals with immunodeficiency. Immunodeficient persons with persistent vaccine-related poliovirus infection may serve as a potential reservoir for reintroduction of polio after wild poliovirus eradication, posing a risk of their further circulation in inadequately immunized populations. Attenuated polioviruses used in oral polio vaccine (OPV) can mutate into vaccine-derived poliovirus (VDPV) and cause poliomyelitis outbreaks. The aim of the study was to determine the duration of vaccine shedding in stool specimens of children <5 years vaccinated with tOPV. The study monitored poliovirus excretion following vaccination among children at an orphanage in Kenya. After national immunization days, serial collection of stool specimens was done from orphanage residents aged <5 years at enrollment until the participants shopped shedding. Data recorded included their HIV status and demographic, clinical, immunological, and immunization data. To detect and characterize isolated polioviruses and non-polio enteroviruses (NPEV), we used viral culture and intratypic differentiation of isolates by real time PCR. Long-term persistence was defined as shedding for >or= 6 months. Twenty-six children (10 HIV-infected, 16 HIV-uninfected) were enrolled, and 80 specimens (21 from HIV-infected, 59 from HIV-uninfected) were collected. All HIV-infected children had CD4 Range of 500-1500 cells/mm³. All participants shed vaccine-related polioviruses at week 2 and 4 and 1 shed NPEV at some point during the study period. Of 54 poliovirus-positive specimens, 20 were from HIV-infected, and 32 from HIV-uninfected children. No participant shed polioviruses for >or= 6 months. The results indicate that both HIV-infected and un-infected children retain the ability to clear enteroviruses, including vaccine-related poliovirus. Larger studies are needed to confirm and generalize these findings. Understanding how mucosal immunity influences shedding patterns in a larger population will help optimize vaccination strategies.
