Safety, Efficacy, and Immunogenicity of a Multivalent Adjuvanted Staphylococcus aureus Vaccine in Adults With Recent Skin and Soft Tissue Infections: An Observer-Blind, Randomized, Placebo-Controlled, Multinational Phase 1/2 Trial.
Eugene Athan, Richard N Greenberg, David A Baker et al.
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In 30 seconds
This observer-blind, randomized, placebo-controlled phase 1/2 trial evaluated a five-antigen Staphylococcus aureus vaccine with AS01E adjuvant in adults, including 194 participants aged 18–64 years with a recent S. aureus skin and soft tissue infection (SA-SSTI). Participants received two vaccine or placebo doses two months apart and were followed for 12 months. The vaccine induced functional immune responses to three antigens, but did not prevent recurrent SA-SSTIs: vaccine efficacy was -38.1% (95% confidence interval, -245.8 to 40.9). Its safety profile was considered acceptable.
Key findings
- At 12 months after dose 2, vaccine efficacy against recurrent SA-SSTIs was -38.1% (95% confidence interval, -245.8 to 40.9).
- The vaccine induced robust functional immune responses against CP5, CP8, and alpha-hemolysin, three of its five antigens.
- Solicited local adverse events were more frequent with vaccine than placebo, mostly mild or moderate; medically attended and serious adverse events occurred at similar frequencies.
Why it matters
The trial highlights that measurable functional immune responses to selected vaccine antigens did not translate into protection against recurrent infection in this population. This distinction matters when interpreting immunogenicity as a potential indicator of clinical benefit. The findings also provide safety information for an adjuvanted vaccine tested in adults with a recent history of SA-SSTI.
What to keep in mind
The phase 2 study stopped enrollment after predefined futility criteria were met at interim efficacy analysis; the reported efficacy estimate has a wide confidence interval.