Poliovirus 1 Seroprevalence in Nova Scotia, Canada

Abstract

Thanks to the efforts of the Global Polio Eradication Initiative, the world has never been closer to eradicating polio as it is today. Without complete eradication from the remaining strongholds, all countries remain at risk. It is the responsibility of polio-free countries to ensure vaccination rates are kept high enough to maintain levels of immunity among the population that prevent reintroduction of poliovirus. Since Nova Scotia has been exclusively using IPV for prevention and control of polio from the time it was licensed in 1955, immunity among adults and seniors may be declining as a result of waning immunity. The risk of virus reintroduction can be assessed by determining the the seroprevalence of neutralizing antibodies in the population. We established and validated the poliovirus standardized microneutralization (MN) assay and developed an immunoadsorption technique to generate poliovirus non-immune serum to use as a negative control. Using the MN assay, we examined the prevalence and levels of neutralizing antibodies against poliovirus 1 (PV1) in Nova Scotia by testing residual sera from three age groups (10 – 29, 30 – 49, and 50 – 64 years old). Although we hypothesized that older adults would have lower levels of antibodies due to waning immunity, seroprevalence rates and geometric mean titers were found to be higher for these age groups. Overall PV1 seroprevalence in Nova Scotia is above the herd immunity threshold range required for protection from poliomyelitis. Seroprevalence rates in the younger age group can be increased by enhancing vaccine uptake and schedule completion. We demonstrated the importance and value of seroepidemiological surveys, and have shown that they provide a more accurate determination of population-based protection than vaccination coverage rates alone. Based on our findings, there is no imminent risk to Nova Scotia from PV1.