Background: Vaccines are biologic medical products, the biological activity and characteristics of which are significantly different from common drugs and other medical products. The process of determining the dosing (vaccination) schedule for a particular vaccine is based on different principles and rules than other drugs. The dosing schedule for drugs is based on the essential pharmacological properties: pharmacokinetics and pharmacodynamics. When determining the schedule for vaccines, the pharmacokinetic and pharmacodynamic principles cannot be applied: sero-conversion and sero-protectivity of the biologically active component of the vaccine need to be applied. As opposed to drugs and medical products the dosing (vaccination) schedule in the Summary of Product Characteristics (SPC) is often provided in several versions, sometimes with a supplement referring to official (national) recommendations. In relation to the large variability vaccination schedules in the European Union (EU), it is not realistic to test each vaccination schedule in clinical studies. Requiring clinical trials for each vaccination schedule used only for the needs of regulators is more of an ethical issue than a scientific one. The European Centre for Disease Prevention and Control (ECDC), which is the Scientific Panel on Childhood Immunisation Schedule (SPACIS), accepts all the schedules used in EU countries as valid.
Methods and results: A review of the literature on immunisation schedules for primary series and booster doses choosing the following key words: immunisation, vaccination schedule, primary, booster, timing, vaccination delay.