Table 3 Summary of methods used by the VIMC for calculating the impact of vaccination (refer to Tables 1–2 for parameter values and for stratifications of the year of vaccination method, respectively)
From: How can the public health impact of vaccination be estimated?
Method | Definition | Advantages | Limitations |
|---|---|---|---|
Calendar year | Impact for a particular year | Intuitive. | Does not account for the long-term impact of vaccination on individual disease risk and cannot be linked to specific vaccination activities. |
Birth year | Impact for a particular birth cohort | Captures the long-term effects of vaccination in protecting those vaccinated. | Duration of modelling needs to be pathogen-appropriate, e.g. the effects of HepB require a longer modelling time frame. Does not account for inter-cohort effects (e.g. herd protection). |
Year of vaccination (YoV) | Impact attributed to year in which vaccination occurred | Possible to assess the effects of a specific year’s activities and thus provide a direct comparison of the number of doses provided and their effect. This is useful for planning and economic purposes. | An impact ratio is required which can be affected by the years/activities or birth cohorts included, see Table 2 for details. Does not account for inter-cohort effects (e.g. herd protection). |