A Survey to Assess Serological Prevalence of Poliovirus Antibodies in Areas With High-Risk for Vaccine-Derived Poliovirus Transmission in Chad

Abstract

Background World Health Organization African region is wild poliovirus-free; however, outbreaks of vaccine-derived poliovirus type 2 (VDPV2) continue to expand across the continent including in Chad. We conducted a serological survey of polio antibodies in polio high-risk areas of Chad to assess population immunity against poliovirus and estimate the risk of future outbreaks. Methods This was a community-based, cross-sectional survey carried out in September 2019. Children between 12 and 59 months were randomly selected using GIS enumeration of structures. Informed consent, demographic and anthropometric data, vaccination history, and blood spots were collected. Seropositivity against all 3 poliovirus serotypes was assessed using a microneutralization assay at Centers for Disease Control and Prevention, Atlanta, GA, USA. Results Analyzable data were obtained from 236 out of 285 (82.8%) enrolled children. Seroprevalence of polio antibodies for serotypes 1, 2, and 3 was 214/236 (90.7%); 145/236 (61.4%); and 196/236 (86.2%), respectively. For serotype 2, the seroprevalence significantly increased with age (P = .004); chronic malnutrition was a significant risk factor for being type 2-seronegative. Interpretation Poliovirus type 2 seroprevalence in young children was considered insufficient to protect against the spread of paralytic diseases caused by VDPV2. Indeed, VDPV2 outbreaks were reported from Chad in 2019 and 2020. High-quality immunization response to these outbreaks is needed to prevent further spread.

Community-based survey to assess seroprevalence of poliovirus antibodies in far-north Cameroon in 2020

“…Hygiene and level of parental education are factors that continuously arise as associations with seropositivity. [13] , [16] , [17] Using toilets at both household- and community- level facilities revealed to be a risk factor in this study; children who defecated in open fields had a higher chance of being seropositive for type 2 poliovirus, consistent with reports from Chad [13] . We hypothesize that open-field defecation can lead to exposure to poliovirus explaining the higher levels of seropositivity.…”

“…The reported values in Chad for 12–23, 24–35, 36–47, 48–59 age groups was 37 %, 48 %, 65 %, 83 %, respectively. [13] For the same age intervals, Niger reported 85 %, 85 %, 89 %, 92 %. [14] Moreover, median titers for serotype 1 were high for all age groups and increased with age for serotype 2, again consistent with studies in Chad, Borno, and Yobe provinces of Nigeria.…”

“… [14] Moreover, median titers for serotype 1 were high for all age groups and increased with age for serotype 2, again consistent with studies in Chad, Borno, and Yobe provinces of Nigeria. [13] , [14] , [15] .…”

Poliovirus antibodies following two rounds of campaigns with a type 2 novel oral poliovirus vaccine in Liberia: a clustered, population-based seroprevalence survey

“…27 Seroprevalence surveys with similar study designs have been implemented recently in Cameroon and Chad. 28 , 29 In Cameroon in 2020, a higher seroprevalence was documented against poliovirus type 1 (87%) and type 3 (79%), while the estimated coverage for third dose bOPV and IPV were similar to those in our study (70% and 69%, respectively). 28 Similarly in Chad, in 2019, the seroprevalences against type 1 (91%) and type 3 (83%) were higher than those in our study, with lower third dose bOPV (47%) and IPV (49%) coverage.…”

“… 28 Similarly in Chad, in 2019, the seroprevalences against type 1 (91%) and type 3 (83%) were higher than those in our study, with lower third dose bOPV (47%) and IPV (49%) coverage. 29 However, population immunity is also attributable to supplementary immunisation activities, the frequency of which differs from country to country. Our findings of low seroprevalence against type 1 and 3 in Liberia are not unexpected given the suboptimal coverage of the routine immunisation programme; however, they are substantially lower than found in Cameroon and Chad.…”