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During surveys, it is recommended that children immunization status should be based on immunization documents. It has been noted that in some communities, a number of children are claimed to be vaccinated but have no evidence of vaccination. This work is proposed to estimate routine immunization coverage in children based on both documented vaccination and the tracking of undocumented immunization. It was a community‑based survey targeting children aged 0‑59 months in which the immunization status of children was assessed based on vaccination documents and based on a questionnaire tracking immunization sites and period for children with undocumented vaccination. The vaccination coverage and completeness were estimated from data collected in immunization cards and re‑estimated after tracking the immunization status of children with no immunization cards. Of 1435 children reached in households, 1430 (99.7%) were included. Of 1072 children aged 12‑59 months, 194 (18.1%) received DPT‑Hi+Hb 3 with evidence and 399 (37.2%) with evidence and tracking. In the same age group, the dropout rate from DPT‑Hi+Hb 1 (157 doses administered) to DPT‑Hi+Hb 3 (127 doses administered) with evidence was 19.1% and 42.4% with evidence and tracking. The tracking of immunization status in children with no evidence of vaccination allows to determine their immunization status and to improve the reliability of the estimated vaccination coverage. This strategy could be adopted to be part of the planning and implementation of vaccination coverage surveys of EPI vaccines.

BackgroundCountries’ Expanded Program on Immunization (EPI) contribute to the reduction of mortality and morbidity, but access to these vaccines remains limited in most low-income countries. ObjectiveWe aim to assess whether involving community volunteers (CVs) to track children’s vaccination status and demographic movements and using recorded data to plan catch-up immunization sessions can improve children’s vaccination timeliness, completeness, and coverage. MethodsThis was a field-based randomized controlled trial and communities of the Foumban health district in West Cameroon were allocated to intervention or control groups. In the intervention group, a CV per community was trained to visit households monthly for a year to assess and record in a register, details of EPI-targeted children, their demographic movements and immunization status. The scanned recorded pages were sent to the health center immunization team through WhatsApp and used to organize monthly community catch-up immunization sessions. In the control group, EPI vaccination sessions were routinely conducted. Surveys were conducted at 6 and 12 months from the beginning of the intervention in both study groups to assess and compare immunization timeliness, coverage, and completeness. ResultsOverall, 30 buildings per cluster were surveyed at midline and endline. Of the 633 and 729 visited households in the intervention group at midline and endline, 630 (99.5%) and 718 (98.4%), respectively, consented to participate. In the control group, 507 and 651 households were visited and 505 (99.6%) and 636 (97.7%), respectively, consented to participate. At 12 months intervention, the month one timeliness of bacille Calmette–Guerin (BCG) vaccine did not increase in the intervention group compared with the control group for the age groups 0-11 months (adjusted odds ratio [aOR] 1.1, 95% CI 0.7-1.8) and 0-59 months (aOR 1.1, 95% CI 0.9-1.4), and significantly increased for the first-year BCG vaccine administration for the age group 0-23 months (aOR 1.5, 95% CI 1.1-2.2). The coverage of diphtheria-pertussis-tetanus and hepatitis B+Hemophilus influenzae type B (DPT-Hi +Hb) dose 3 (aOR 2.0, 95% CI 1.5-2.7) and of DPT-Hi+Hb dose 1 (aOR 1.8, 95% CI 1.4-2.4) vaccines increased significantly in the intervention group compared with the control group in the age groups 12-59 months and 12-23 months, respectively. Specific (DPT-Hi+Hb dose 1 to DPT-Hi+Hb dose 3: aOR 1.9, 95% CI 1.4-2.6) and general (BCG to measles: aOR 1.5, 95% CI 1.1-2.1) vaccine completeness increased significantly in the intervention group compared with the control group. ConclusionsFindings support that involving CVs to track children’s vaccination status and demographic movements and using recorded data to plan catch-up immunization sessions improve children’s vaccination timeliness, completeness, and coverage. This strategy should be adopted to improve access to vaccination for EPI target populations and the consistency verified in other contexts. Trial RegistrationPan African Clinical Trials Registry PACTR201808527428720; https://pactr.samrc.ac.za/TrialDisplay.aspx?TrialID=3548