Assessing the health and economic impact of disease on a given population is the first step towards prioritization and adoption of appropriate vaccination policies and disease control strategies. After a vaccine has been introduced, assessing the impact of vaccination on disease is an effective way to measure progress, guide programme development and advocate for continuing program support.  These impact assessments require reliable data on disease burden, measured by indicators such as morbidity and mortality rates, and collected through ongoing surveillance and reporting activities.  The type of surveillance for a particular disease depends on the attributes of that disease and the immunization programme’s objectives. WHO provides recommended standards for surveillance of VPDs, and makes data available in a consolidated format for each VPD.

WHO-coordinated surveillance networks have been established for specific VPDs to provide support to Ministries of Health and surveillance sites. Because some illnesses such as diarrhoea or fever/rash can be caused by several pathogens, global laboratory networks are needed to accurately confirm if the cause is a specific VPD organism, such as rotavirus or measles.

In 2017, WHO and UNICEF disseminated the surveillance questionnaire together with the Joint Reporting Form to all 194 WHO Member States. The questionnaire requested information on the current status of surveillance for 28 current and potential future VPDs, attributes of surveillance conducted for each VPD, and details about current measles and rubella surveillance system(s) in each country.