This project studies a working but manual immunization system in place in Pakistan, subject to concerns such as poor record-keeping, reaching targeted children and unavailability of latest census. We propose an openEHR-based solution, called Light-weight Electronic Traceable and Updatable System (LETUS), which aims at increasing childhood immunization coverage and traceability. Two key modules of the solution include: (1) a service that collects the data from the immunization workers, computes population estimates for particular regions, and creates alerts if the ratio of vaccinations over population in a region falls outside a certain range (over or under), and (2) several "thin client" modules where workers can enter their collected data and receive feedback about the current coverage in their region. The proposed software system can be integrated into existing regional immunization registry systems, and run on the servers of a local health agency to ensure timely reporting. Within each immunization registry systems, children data is sharable by applying openEHR approach. This solution will gradually replace the current record keeping process by employing smart phone applications and web services.