Although modern vaccines are safe, the increased number of doses and opportunities for vaccination may lead to vaccine safety concerns. Assured quality vaccines are essential to effective immunization programmes.
Monitoring vaccine safety is a complex and shared responsibility. It can be carried out in many ways: large post-approval clinical trials, record linkage studies that track health care visits following vaccinations, or more targeted follow-up studies such as those using health diaries. However, the cornerstone of surveillance systems in most countries is active and passive reporting schemes that rely on the vigilance of health care providers and the reporting of individual cases of adverse reactions.
As part of safety monitoring we are also looking for vaccine safety “signals“ – new events which have not been previously known to be caused by the vaccine. or a potential increase in frequency of a known event in recipients of the vaccine as compared to those who have not received it.
A standardized evaluation instrument known as the causality assessment form has been developed to establish causality. This form assesses different points: biological plausibility, the time elapsed between the vaccine administration and onset of the adverse event, and whether other factors could account for the adverse symptoms. The form concludes with a consensus assessment causality, a commentary about the assessment, and advice for further study or follow-up.