Global Vaccine Safety

Investigation of safety signals

To strengthen the ability of countries to evaluate vaccine safety signals

A vaccine safety signal is information that indicates a potential link between a vaccine and an event previously unknown or incompletely documented, that could affect health. The signal, which may come from one or multiple sources, will suggest a new potentially causal association (or a new aspect of a known association) between a vaccine and an event (or a set of related events), which could be either adverse or beneficial.

Epidemiological studies are usually needed to assess the causal relationship between the vaccine and the signal. The design of such studies can vary widely depending on the circumstances. Pathological or laboratory studies may also be required to provide evidence of the causal link. National expert committees, where they exist, advise local authorities on the nature of the observed events and propose appropriate investigations. However, many countries do not have the capacity to carry out such studies.

The GVSI aims to ensure that safety signals will be assessed wherever they may occur and that appropriate action will be taken. It is difficult to identify very rare events (i.e. those that occur less than once in a million doses of vaccine). New methodologies using computerized medical databases – with data from multiple centres (and sometimes multiple countries) – are needed to assess these rare events. Such resources are being developed through international collaboration within the GVSI.


For national capacity to investigate a signal

A pool of national, regional and global experts is available to assist in this effort and support capacity-building. Interested in joining the roster? Kindly contact to request access to complete your profile.

August 2019

Contact us

Global Vaccine Safety Initiative
World Health Organization