Academic journal article Bulletin of the World Health Organization

Monitoring Signals for Vaccine Safety: The Assessment of Individual Adverse Event Reports by an Expert Advisory Committee

Academic journal article Bulletin of the World Health Organization

Monitoring Signals for Vaccine Safety: The Assessment of Individual Adverse Event Reports by an Expert Advisory Committee

Article excerpt

Introduction

The continuous monitoring of the safety of drugs once they are licensed and in widespread use is a complex and shared responsibility between governments, industry, health care providers and patients. This responsibility is all the more important for vaccines, which are administered on a large scale to healthy individuals for anticipated benefits. Vaccines demand a very high degree of safety. Parents of infants receiving their routine immunizations need reassurance that vaccines are safe.

The safety monitoring of any drug licensed for use can take many forms, including large post-approval clinical trials, record linkage studies that track health care visits following vaccination, or more targeted follow-up studies such as those using health diaries. However, the cornerstone of surveillance systems in most countries is passive reporting schemes that rely on the vigilance of health care providers (1) to detect events that are felt to be due to the administration of a drug product (vaccines in this case), and their reporting of these cases to a regional or national authority or to the manufacturing company. In Canada the systems in place to monitor vaccine safety include active surveillance for serious reactions that would result in admission to a paediatric hospital, in addition to the voluntary (spontaneous) reporting system (2-4). Both these systems rely on the collection of case reports, and an intimate partnership between the provincial and territorial ministries of health and the Vaccine-Associated Adverse Events Surveillance Program in the Division of Immunization, Bureau of Infectious Diseases, at Health Canada. The majority of case reports are submitted by public health nurses, especially in those provinces where immunization delivery is mainly through public health clinics. Physicians report less than 10% of the cases, while the public is asked to report through their physician or public health unit rather than directly to improve not only the diagnosis and reporting per se, but also to ensure that the vaccine provider is made aware of the alleged event. Because the system is so well established through public health channels, manufacturers receive few case reports directly (less than 5%). Reporting is voluntary in all provinces except one, Ontario, where selected events are part of the same mandatory reporting legislation as reportable infectious diseases. Nevertheless, reporting rates are not improved by this requirement. There are a variety of reasons why physicians report so poorly overall, the most important being lack of awareness of the reporting system and its criteria, rather than the burden of reporting (5). This limitation is significant as the diagnosis of the most serious adverse events relies on reporting by physicians.

Data analysis is a complex undertaking, whose ultimate goal is the search for signals that may trigger immediate action to alter or suspend the use of a vaccine or vaccine lot, suggest changes to the product labelling, or lead to the initiation of formal clinical or epidemiological trials to confirm or refute the concern. To the best of our knowledge, a major intervention regarding the use of a vaccine has only been required twice in Canada. The only occasion that a safety concern arose was the withdrawal in 1987 of a measles-mumps-rubella (MMR) vaccine containing the Urabe strain of mumps vaccine which posed an excess risk of aseptic meningitis in the country (6). There was a later recall of an MMR product from the field on discovery of vials that reconstituted poorly and were discoloured. It turned out that a packaging unit had "caramelized" the product.

The information supplied in adverse-event case reports relating to vaccines varies in quality and completeness. Practitioners are encouraged to submit cases that are mere suspicions, and need not have a known causal relationship. As a result, a critical assessment of individual case reports is necessary to determine if some plausible relationship really exists between the vaccination and the adverse event described, or whether the link with vaccination was a coincidence while the adverse event was due to an underlying illness. …

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