Evaluation of a recombinant five-antigen Staphylococcus aureus vaccine: The randomized, single-centre phase 1a/1b clinical trials

•rFSAV is a novel recombinant five-antigen Staphylococcus aureus vaccine.•Three immunization doses and four procedures were evaluated in phase 1a and 1b.•rFSAV is safe, well tolerated in healthy adults.•rFSAV elicits rapid and robust specific humoral and cellular immune responses.•Optimal perioperative regimen is worth further evaluation in targeted population. Staphylococcus aureus is an important pathogen that causes hospital and community infections. To control Staphylococcus aureus infection and reduce the usage of antibiotics, we evaluated the safety and immunogenicity of a recombinant five-antigen Staphylococcus aureus vaccine (rFSAV) in healthy adults. We conducted a randomized, double-blind, placebo-controlled phase 1a study and a randomized, open-label phase 1b study. In phase 1a, we randomly allocated 144 healthy participants in a ratio of 1:1:1:1 to receive the low-(60 μg), middle-(120 μg), and high-dose (240 μg) vaccine or placebo at day 0, 3, 7 and 14. In phase 1b, 144 healthy participants were randomly allocated at a ratio of 1:1:1:1 to receive 0–3–7, 0/0–7, 0/0–3–7, 0/0–7–14 regimens to estimate the optimal strategy. The primary study endpoint was the incidence of solicited adverse events post-vaccination. The immunogenicity endpoints included the level of specific antibodies to five antigens after vaccination, as well as the cellular immune responses and functional antibodies. There were 31 (86%), 30 (83%), and 32 (89%) of 36 participants in the low-, middle-, and high-dose group reported solicited adverse events, respectively, most of the adverse events were mild or moderate. In phase 1b, the dose-adjusted rFSAV (90 μg) showed a better safety profile in the four immune procedures, and no vaccine-related serious adverse events were reported. The antigen-specific binding antibodies started to increase at day 7 and reached the peak around day 14 to 21. The cellular immune responses and functional antibodies also were substantially above background levels. rFSAV is safe, well tolerated in healthy adults, elicits rapid and robust specific humoral and cellular immune responses with unconventional immunization procedure in phase 1a and 1b. It deserves to be noted and further explored. Clinical Trials Registration: NCT02804711 and NCT03966040.