Two-year persistence of MERS-CoV-specific antibody and T cell responses after MVA-MERS-S vaccination in healthy adults.

MVA-MERS-S, a vaccine candidate against Middle East respiratory syndrome (MERS), was recently evaluated in a randomized, placebo-controlled, double-blind phase 1b clinical trial to assess its safety, immunogenicity, and optimal dosing in healthy adults in Hamburg and Rotterdam. A three-dose regimen was safe and elicited robust spike-specific antibody responses. We extended this trial to assess the two-year durability of MERS-CoV-specific antibody and T cell responses in 48 study participants of the Hamburg cohort. Our findings show that immune responses remain detectable for at least 24 months after the third vaccination. Antibodies persisted at levels comparable to the peak response observed after the second vaccination and were able to cross-neutralize MERS-CoV spike mutants. Although the immune correlates of protection against MERS remain unknown, the observed durability of humoral and cellular immune responses supports the potential of MVA-MERS-S as a promising MERS vaccine candidate and highlights the importance of a booster dose in sustaining long-term immunity.