Safety and immunogenicity of a modified-vaccinia-virus-Ankara-based influenza A H5N1 vaccine: a randomised, double-blind phase 1/2a clinical trial

Summary Background Modified vaccinia virus Ankara (MVA) is a promising viral vector platform for the development of an H5N1 influenza vaccine. Preclinical assessment of MVA-based H5N1 vaccines showed their immunogenicity and safety in different animal models. We aimed to assess the safety and immunogenicity of the MVA-haemagglutinin-based H5N1 vaccine MVA-H5-sfMR in healthy individuals. Methods In a single-centre, double-blind phase 1/2a study, young volunteers (aged 18–28 years) were randomly assigned with a computer-generated list in equal numbers to one of eight groups and were given one injection or two injections intramuscularly at an interval of 4 weeks of a standard dose (108 plaque forming units [pfu]) or a ten times lower dose (107 pfu) of the MVA-H5-sfMR (vector encoding the haemagglutinin gene of influenza A/Vietnam/1194/2004 virus [H5N1 subtype]) or MVA-F6-sfMR (empty vector) vaccine. Volunteers and physicians who examined and administered the vaccine were masked to vaccine assignment. Individuals who received the MVA-H5-sfMR vaccine were eligible for a booster immunisation 1 year after the first immunisation. Primary endpoint was safety. Secondary outcome was immunogenicity. The trial is registered with the Dutch Trial Register, number NTR3401. Findings 79 of 80 individuals who were enrolled completed the study. No serious adverse events were identified. 11 individuals reported severe headache and lightheadedness, erythema nodosum, respiratory illness (accompanied by influenza-like symptoms), sore throat, or injection-site reaction. Most of the volunteers had one or more local (itch, pain, redness, and swelling) and systemic reactions (rise in body temperature, headache, myalgia, arthralgia, chills, malaise, and fatigue) after the first, second, and booster immunisations. Individuals who received the 107 dose had fewer systemic reactions. The MVA-H5-sfMR vaccine at 108 pfu induced significantly higher antibody responses after one and two immunisations than did 107 pfu when assessed with haemagglutination inhibition geometric mean titre at 8 weeks against H5N1 A/Vietnam/1194/2004 (30·2 [SD 3·8] vs 9·2 [2·3] and 108·1 [2·4] vs 15·8 [3·2]). 27 of 39 eligible individuals were enrolled in the booster immunisation study. A single shot of MVA-H5-sfMR 108 pfu prime immunisation resulted in higher antibody responses after the booster immunisation than did two shots of MVA-H5-sfMR at the ten times lower dose. Interpretation The MVA-based H5N1 vaccine wa