2. Follow-up Form: For the follow up visits by the caregivers to get the subsequent vaccinations (3 - 4 visits), field workers will be based at the participating EPI centers throughout the follow-up period. Each follow-up visit takes about 10-15 minutes of the caregivers time, not including any time spent waiting to be seen by the vaccinator. Each child in the study is provided a unique EPI number by the EPI staff as per routine and also a study ID by a field worker. The linkage between the EPI number and the ID number will be maintained after data collection is complete. The field workers will use these IDs to identify the study participants when they come for follow-up visits. At each follow up visit, the field worker will record the vaccine administered and date for each child in the study, including verifying data on past immunizations and due vaccines (follow-up form attached). Therefore, for each study participant, the field workers would collect data 3-4 times during the follow-up period. The minimum duration of follow up provided to each participant will be until the child receives Measles-1 vaccine (given at 9 months of age per WHO recommendations). The maximum duration of follow up provided to each participant will be 11 months.