Poliovirus immunity among adults in the Democratic Republic of the Congo: a cross-sectional serosurvey

Background: Vaccination efforts to eradicate polio currently focus on children under 5 years of age, among whom most cases of poliomyelitis still occur. However, in the Democratic Republic of the Congo (DRC), an outbreak of wild poliovirus type 1 occurred in 2010-2011 in which 16% of cases occurred among adults; in a related outbreak in the neighboring Republic of Congo, 75% of cases occurred among the same adult age-group. Given that infected adults may transmit poliovirus, this study was designed to assess adult immunity against polioviruses.

Methods: We assessed poliovirus seroprevalence using dried blood spots from 5,526 adults aged 15-59 years from the 2013-2014 Demographic and Health Survey in the DRC.

Results: Among adults in the DRC, 74%, 72%, and 57% were seropositive for neutralizing antibodies for poliovirus types 1, 2, and 3, respectively. For all three serotypes, seroprevalence tended to be higher among older age groups, those living in households with more children, and among women.

Conclusions: Protection against poliovirus is generally low among adults in the DRC, particularly for type 3 poliovirus. The lack of acquired immunity in adults suggests a potentially limited poliovirus circulation over the lifetime of those surveyed (spanning 1954 through 2014) and transmission of vaccine-derived poliovirus in this age group while underscoring the risk of these outbreaks among adults in the DRC.