Safety and immunogenicity of a booster dose of a 3-antigen Staphylococcus aureus vaccine (SA3Ag) in healthy adults: A randomized phase 1 study

- A booster dose of a 3-antigen Staphylococcus aureus vaccine (SA3Ag) was assessed.
- SA3Ag is a novel multiantigen vaccine that targets S. aureus virulence factors.
- Immune response to the 1st vaccination persisted for 12 months in adults ≤85 years.
- Little or no additional immune response induced by booster dose given at Month 6.
- Injection site reactions post-booster more frequent and severe but self-limiting.

SummaryObjectiveA 2-stage, phase 1, randomized, placebo-controlled study in healthy adults to assess immunogenicity and safety of a booster dose at three dose levels of a 3-antigen Staphylococcus aureus vaccine (SA3Ag) containing recombinant clumping factor A (ClfA) and capsular polysaccharides 5 and 8 (CP5 and CP8) conjugated to a diphtheria toxoid.MethodsSix months after initial single vaccination, in Stage 2, SA3Ag recipients were randomized (1:1) to booster vaccination or placebo, while Stage 1 placebo recipients received placebo again. Pre- and post-vaccination blood samples were analyzed.ResultsIn Stage 2 (n = 345), pre-booster CP5 and CP8 titers remained high with no increase post-booster. ClfA titers remained high after initial vaccination and increased post-booster, approaching the peak response to the initial dose. Post-booster local reactions were more frequent and of greater severity than reported after the initial vaccination, particularly for the high-dose level recipients. Post hoc analysis showed no dose-response pattern and no obvious association between diphtheria toxoid titers and local reactions after initial or booster vaccination.ConclusionImmune responses after the initial vaccination persisted for the 12 months studied, with little additional response after the booster dose at 6 months. Post-booster injection site reactions were more frequent and more severe but self-limiting.Clinicaltrials.gov identifierNCT01018641.