Howard E. Gary

Immunodeficient persons with persistent vaccine-related poliovirus infection may serve as a potential reservoir for reintroduction of polioviruses after wild poliovirus eradication, posing a risk of their further circulation in inadequately immunized populations. To estimate the potential for vaccine-related poliovirus persistence among HIV-infected persons, we studied poliovirus excretion following vaccination among children at an orphanage in Kenya. For 12 months after national immunization days, we collected serial stool specimens from orphanage residents aged or= 6 months. Twenty-four children (15 HIV-infected, 9 HIV-uninfected) were enrolled, and 255 specimens (170 from HIV-infected, 85 from HIV-uninfected) were collected. All HIV-infected children had mildly or moderately symptomatic HIV-disease and moderate-to-severe immunosuppression. Fifteen participants shed vaccine-related polioviruses, and 22 shed NPEV at some point during the study period. Of 46 poliovirus-positive specimens, 31 were from HIV-infected, and 15 from HIV-uninfected children. No participant shed polioviruses for >or= 6 months. Genomic sequencing of poliovirus isolates did not reveal any genetic evidence of long-term shedding. There was no long-term shedding of NPEV. The results indicate that mildly to moderately symptomatic HIV-infected children retain the ability to clear enteroviruses, including vaccine-related poliovirus. Larger studies are needed to confirm and generalize these findings.

SUMMARY: While oral polio vaccine (OPV) has been shown to be safe and effective, it has been observed that it can circulate within a susceptible population and revert to a virulent form. Inactivated polio vaccine (IPV) confers protection from paralytic disease, but provides limited protection against infection. It is possible, then, that an IPV-immunized population, when exposed to OPV, could sustain undetected circulation of vaccine-derived poliovirus. This study examines the possibility of polio vaccine virus circulating within the United States (highly IPV-immunized) population that borders Mexico (OPV-immunized). A total of 653 stool and 20 sewage samples collected on the US side of the border were tested for the presence of poliovirus. All samples were found to be negative. These results suggest that the risk of circulating vaccine-derived poliovirus is low in fully immunized IPV-using populations in developed countries that border OPV-using populations.

Background Recent outbreaks of poliomyelitis caused by vaccine-derived virus have raised concerns that vaccine-derived poliovirus may continue to circulate after eradication. In these outbreaks, the virus appears to have replicated for ≥2 years before detection. Early detection is critical for an effective response to these outbreaks. Although acute flaccid paralysis (AFP) surveillance will remain the standard for poliovirus detection, wastewater sampling could be a useful supplement. In this study, we evaluated the sensitivity of wastewater sampling by concurrently collecting stools from children aged Methods Sample collection was begun during the third week after the national immunization campaign, continued weekly through the seventh week, and was repeated during weeks 15 and 19. Virus detection and titration were performed using both cell culture and polymerase chain reaction techniques. Results Wastewater sampling was found to be at least as sensitive as stool sampling under these conditions. Poliovirus was isolated from children through week 7, suggesting that viral shedding reached undetectable levels between weeks 8 and 14. The last virus-positive wastewater sample was collected during week 15. Conclusions Wastewater sampling under the conditions studied can be a sensitive supplement to AFP surveillance. Similar studies under different conditions are needed to determine the role of wastewater sampling in post-eradication surveillance.

Surveillance for cases of acute flaccid paralysis provides a means for detecting circulating wild poliovirus in a population and therefore is crucial to the global polio eradication effort. An initial step toward developing a more general framework for understanding the sensitivity of the acute flaccid paralysis surveillance system is presented by first specifying four categories of sensitivity involved: laboratory sensitivity, specimen sensitivity, person sensitivity, and population sensitivity. Using this framework, estimates for specimen sensitivity (the probability that virus will be detected in a specimen collected from an infected person) and the prevalence of infection are derived and applied to surveillance data from three regions. On the basis of the framework, our analysis indicates that a second specimen may significantly increase person sensitivity under some circumstances but provides little improvement under others.

A basic framework for describing sensitivity of surveillance to detect poliovirus is extended from individuals to general populations (population sensitivity). Using the mathematical formulations for population sensitivity, the theoretical behavior of surveillance sensitivity under various conditions is analyzed. As a region nears the elimination of poliovirus, population sensitivity falls to a value lower than the case-to-infection ratio, regardless of the system proficiency. Also, a second stool specimen makes a substantial contribution to population sensitivity only in regions with relatively low specimen sensitivity and then only over a narrow range of population infection incidence. Estimates of the mean numbers of infected and uninfected acute flaccid paralysis cases investigated in a season are derived. These may serve as additional indicators of system operation but require the collection of 2 specimens per case.