Immunization, Vaccines and Biologicals

Immunization highlights: 2012

Ensuring safe vaccines of assured quality

WHO vaccine reaction rates information sheets

An important part of post-licensure vaccine safety surveillance is to collect and analyze reports of adverse events following immunization (AEFI). Analyzing multiple AEFI reports help determine if the observed reaction rate to a specific vaccine is higher than the expected vaccine reaction rate which is often determined from published studies or vaccine trials. If a vaccinated group and a placebo group have identical background rates of an event, any differences between groups can be attributed to the vaccine, taking into account factors leading to variation of background, observed and vaccine reaction rates of events.

To help strengthen the capacity to introduce vaccines in Member States, WHO has now made available information sheets providing details on a total of 10 selected vaccines that are relevant to the analysis of reported events: Anthrax, Bacillus Calmette-Guérin (BCG), Haemophilus influenza type B (Hib), hepatitis A and B, influenza, human papillomavirus (HPV), pneumococcal, rabies, varicella zoster. In total, information sheets for over 20 of the most important licensed vaccines will be developed and posted on the IVB website, in due course.

These information sheets include a short summary of the vaccine as well as details of mild and severe adverse reactions (local and systemic) following immunization. Where possible, the information presented includes the expected rates of vaccine reactions as published in the literature.

The information sheets are primarily for national public health officials and immunization programme managers but may appeal to others interested in such information. Data from these sheets can be used in the evaluation of AEFI reported during national immunization programmes, but also in preparing communication materials about specific vaccines.

Related link

List of WHO contracted laboratories for vaccine prequalification now online

The independent testing of vaccines is part of the procedure for evaluation of the acceptability, in principle, of vaccines for purchase by United Nations agencies. The testing is performed to assess the consistency of final product characteristics and represents one of the decision making criteria for granting prequalification. Tests undertaken are the most relevant to reflect the quality, safety and efficacy of the vaccines and the vaccines must comply with WHO recommended requirements and the UN tender specifications.

Once the vaccines are prequalified, there is continual monitoring for compliance with the established specifications through regular testing of lots of vaccine that have been shipped to countries. For this purpose, manufacturers are required to keep aside, pending request from WHO, samples of each of the vaccine lots shipped to countries through the UN procuring agencies. Independent testing may also be required on occasions in response to complaints from the field or following reports of adverse events following immunization (AEFI) when a quality problem is suspected.