Before licensure, vaccines' safety is thoroughly evaluated in early and late phase clinical trials to ensure safety standards are met. Without achieving optimal safety standards, vaccines cannot be licenced for use. In addition, the WHO Vaccine Prequalification ensures adherence to high-quality standards of safety. Furthermore, as the vaccines get administered to millions of people globally, the WHO regularly reviews the safety profile of these vaccines based on reported information. Regular reviews of available information on vaccines' safety are done using evidence-based principles. On completion of such assessments, the WHO issues revised position papers on each of the vaccines.

Like the medicines which show side effects to some and not all patients during treatment, so do the vaccines when administered to the targeted persons: a few people may experience adverse events following immunisation (AEFI). Most common AEFI are mild such as fever. In rare cases, AEFI can be severe, requiring hospitalisation.

According to the CDC, from 2006 to 2019 over 4 billion doses of covered vaccines were distributed in the United States. For petitions filed in this time period, 8,719 petitions were adjudicated by the Court, and of those, 6,222 were compensated. This means for every 1 million doses of vaccine that were distributed, approximately one individual was compensated (HRSA).  

An AEFI may occur due to the following: the vaccine itself, vaccine-quality defect, error during administration, immunisation anxiety or coincidental. More details on the different causes of AEFI can be found here. 

The WHO Global Vaccine Safety Initiative (GVSI) has developed a blueprint document that proposes a strategic plan for strengthening vaccine safety activities globally.

Optimal vaccine safety is critical to improving the uptake of vaccines as well as building public confidence in these life-saving interventions. Vaccine safety is therefore central for any immunisation programme aiming to achieve reduction, elimination or eradication of vaccine-preventable diseases, as is the case with smallpox.

The National Immunization Technical Advisory Group (NITAG) Support Hub (NISH) is a project of VACFA, a member of WHO Vaccine Safety Net (VSN). NISH supports the critical work of VSN members, including ensuring reliable information on vaccine safety is made available to the public through online platforms such as websites and other applications.

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