VLA15-221 is a randomized, observer-blind, placebo controlled, multicenter Phase 2 study, which is set up in two parts:

Main Study Phase (Part A) and Booster Phase (Part B).

In Part A 600 subjects aged 5-65 years will be enrolled 1:1:1 into three groups: Group 1 will be vaccinated with VLA15 at Month 0-2-6, Group 2 will be vaccinated with VLA15 at Month 0-6 and with placebo at Month 2 and Group 3 will be vaccinated with placebo at Month 0-2-6.

In Part B a subset of subjects will receive a booster injection with VLA15 or placebo at Month 18.