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 ( prequalifies vaccines with the aim of ensuring 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. The regular reviews of available information on vaccines' safety is done using evidence based principles. On completion of such reviews, 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 immunization (AEFI). Most common AEFI are mild such as fever. In some 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 U.S. 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 1 individual was compensated (  

An AEFI may occur due to the following: vaccine itself; vaccine-quality defect; error during administration; immunization anxiety or coincidental. More details on different causes of AEFI can be found here. The Global Vaccine Safety Initiative (GVSI)  has developed a blueprint document that proposes a strategic plan for strengthening vaccine safety activities globally.

Optimal vaccines’ safety is critical to improve uptake of vaccines as well as building public confidence on these lives saving interventions. Vaccines’ 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.

VACFA is a member of Vaccines Safety Net project (VSN). The VSN members ensures reliable information on vaccines safety is made available to the public through online platforms such as website.

There are known myths and incorrect information about vaccines' safety and immunization available in the public domain. Visit the WHO EURO document myths and facts about immunization: 

Are you interested on learning more about vaccines' safety? There is an e-learning course by WHO (


Page created on 16 March 2015

Page last updated on 14 February 2022