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

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.

Response to Poliovirus Outbreaks in the Lake Chad Sub-Region: A GIS Mapping Approach.

The geographic information system (GIS) mapping was used to improve the efficiency of vaccination teams. This paper documents the process in the deployment of geographical information system in response to polio eradication in Chad. It started with a careful review of government official documents as well as review of literature and online resources on Chad, which confirmed that official boundaries existed at two levels, namely Regions and Districts. All settlement locations in the target Districts were identified by manual feature extraction of high-resolution, recent satellite imagery, and map layers created for the following categories: hamlets, hamlet areas, small settlements, and built-up areas (BUAs). This clearly improved microplanning and provided valuable feedback in identifying missed settlements, leading to increased coverage and fewer missed children.

Use of Call Centers in Polio Eradication Efforts in Island Settlement in Chad.

BACKGROUND: One of the four key strategies of the Global Polio Eradication Initiative (GPEI) is high immunization coverage, with oral polio vaccine as part of routine immunization schedules. However, given the weak routine immunization structures in the African Region, coverage is enhanced with supplemental immunization activities (SIAs), and mop-up immunizations. Unfortunately, anecdotal information show that vaccination teams sometimes omit some catchments areas without immunization. This paper thus describes the use of "Call Centers" in detecting missed populations and taking prompt corrective action. METHOD: The study was based on review of call records during polio supplemental immunization campaigns in Bol Districts in Chad from February to May 2018. The immunization coverage resulting from these campaigns was compared with that of February 2018. A compilation of data - details on communities, community leaders, and their phone numbers was performed. On the eve of the campaign, community leaders were alerted on the vaccinators' visitThe community leaders were called on the eve of the campaign to alert them on the visit of the vaccinators. At the end of each day, activities (visits as well) were reviewed at the coordination centres Vaccinators were asked to return to any community where community leaders did not confirm visits). RESULT: Telephone calls allowed the verification and confirmation of the vaccinators visits in 92% of cases. Villages where vaccination was planned but which were not reached were revisited. More than 1,011 children were caught up through this approach in 10 villages in the Bol district. CONCLUSION: In conclusion, call centers played significantly higher role in generating covering more children with immunization during immunization campaign.

Pertussis resurgence in Canada largely caused by a cohort effect.

BACKGROUND: Beginning in 1990 Canada experienced a resurgence of pertussis. Changes in incidence and hospitalization according to age in the province of Quebec between 1983 and 1998 were examined to assess the presence of a cohort effect resulting from a poorly protective vaccine. METHODS: The source of data on incident cases was pertussis notifications to the Quebec Ministry of Health and Social Services. Hospitalization data were extracted from the administrative database that collects information on each hospitalization. RESULTS: The mean annual incidence before 1990 was 3.8 cases per 100,000 population which increased to 37.2 thereafter. Infants had the smallest increase (2.7-fold) when compared with children between 1 and 19 years who experienced a 9- to 15-fold increase and with adults (22.5-fold). The mean annual hospitalization rates increased from 2.7 per 100,000 before 1990 to 5.2 afterward. Ninety percent of hospitalizations occurred in children <5 years of age. The proportion of cases in 0- to 4-year-old children decreased, whereas it increased steadily in all other age groups during the entire study period. Between 1990 and 1998 the median age of cases shifted from 4.4 to 7.8 years. Pertussis affected predominantly children who were immunized with a vaccine introduced in the mid-1980s. The evolution of the age distribution of cases paralleled the aging of this cohort with a slow but steady drift of disease from early childhood to adolescence. CONCLUSION: The sudden increase in pertussis incidence in Canada can be largely attributed to a cohort effect resulting from a poorly protective pertussis vaccine used between 1985 and 1998.