Abstract
The purpose of seasonal influenza vaccination is to prevent its spread. The vaccines contain strains of the influenza virus recommended and approved for a particular season. Just like any other medicinal product, all vaccines require marketing approval. Batches of approved vaccines are extensively tested by the manufacturers and additionally controlled by the approving authorities, which issue the quality control certificates. This article not only to describes the legal background of quality control, but also how control test results obtained by a Croatian official control laboratory are compared to manufacturer's results. We have found that testing results can slightly differ depending on methods/analytical procedures used in different laboratories. This investigation has also shown how important it is to test finished medicinal products, independently of testing at intermediate stages, and how retesting by control authorities ensures that marketed vaccines meet quality standards.