[Adverse events after vaccination].

When the diseases we try to prevent through vaccination are rare, we tend to focus more on the associated risks. Vaccination has led to unfortunate consequences, mainly due to production failure and inadequate control in earlier years. The requirements for vaccine control are now so rigorous that the risk for such occurrences is close to zero. Local and mild systemic reactions to vaccines are rather common, and are usually well known and described in detail when a vaccine is licensed. Some vaccine reactions are however so rare that they only will be discovered through surveillance after the vaccine has become available for routine use. Suspicion of adverse events will now normally arise through the official notification systems for adverse events. Large epidemiological studies are often necessary to decide whether there is a causal relationship or only a coincidence. Recording of adverse events following vaccination and transparency about their existence, are important issues in the work to maintain the credibility of vaccines.