Medicines and vaccines have changed the way in which diseases are prevented and treated. Despite their benefits, medicinal products may have unexpected effects. Some of these effects are unfavorable, ranging in intensity (severity), seriousness and frequency within the intended population. 

While medicines and vaccines are studied in well controlled clinical trials and reviewed by regulatory authorities with the aim of ensuring benefits outweigh risks, some adverse effects are observed only once the product is authorized by regulators and used by a larger population in ‘real world conditions’, including special populations such as children, pregnant women and the elderly.  It is therefore essential that medical products continue to be monitored for their effectiveness and safety post release.

When an alert is issued, it means that the available surveillance tools are working. In practice this means having in place a well-functioning pharmacovigilance system.