Vaccine quality, efficacy and safety


Very few public-health interventions have been as successful as immunizations in providing substantial and highly cost-effective improvements to human health, particularly to that of children. Hundreds of millions of doses of vaccine are used every year; and both their safety and efficacy determine the success of national programmes to control vaccine-preventable diseases.

Vaccines are safe

Vaccines are vigorously tested and proven safe before being licensed and introduced into national immunization programmes. Normal side effects are minor; however in rare cases individuals can have a mild or serious reaction to a vaccine. Most events thought to be related to the administration of a vaccine are actually not due to the vaccine itself. Many are simply coincidental events, while others (particularly in developing countries) are due to human or programme error.

However, as incidence of vaccine-preventable diseases continues to decline, some people have become increasingly concerned about the risks associated with the vaccines, and less fearful of the diseases they are designed to prevent. Failure to deal rapidly and effectively with allegations of vaccine-related adverse events can undermine confidence in a vaccine and ultimately reduce immunization coverage and increase disease incidence.

Quick response in the event of abnormalities 

The surveillance of adverse events following immunization (AEFI) is a critical monitoring function of national regulatory authorities (NRA) and immunization programmes. Surveillance allows programmes to detect abnormalities in the vaccine or programme errors. This is of utmost importance, especially during vaccination campaigns such as measles-rubella supplementary immunization activities, when a large number of doses are administered in a short time.

WHO supports countries in ensuring the quality and safety of vaccination through the strengthening of: 

  • national regulatory authorities (NRA) 
  • AEFI surveillance, reporting, investigation and causality assessment practices.

WHO has a Global Advisory Committee on Vaccine Safety (GACVS) to respond promptly, efficiently and with scientific rigour to vaccine safety issues, and together with the United Nations Children's Fund (UNICEF), it also advise countries on how to communicate and work positively with the media on AEFI issues.