Kleb4V is a tetravalent bioconjugate vaccine including O antigen-polysaccharides of the most predominant Klebsiella pneumoniae serotypes, which will be formulated with or without Adjuvant System, AS03. Study participants will be randomized towards Kleb4V Low dose with or without AS03, Kleb4V Target dose with or without AS03, or placebo.~The study will be conducted in two steps. In Step1 (safety cohort): safety and tolerability of Kleb4V without and with Adjuvant AS03 will be evaluated first in adults of 18-40 y, and subsequently in the target population of older adults 55-70 y. Enrolment will be staggered in groups of small numbers to the different doses and formulations.~In Step 2 (target cohort): Older adults (55-70y) will be concomitantly randomized to receive 1 of the 4 different vaccine formulations or placebo.
In this study, the tetravalent bioconjugate candidate vaccine Kleb4V will be tested to obtain first-time-in-human (FTIH) data on its safety and immunogenicity in healthy adults.