For memory B-cell analysis but not plasmablast analysis, to induce memory B-cell differentiation into antibody-secreting cells, 1 106 PBMCs were stimulated with 10 ng/mL lectin pokeweed mitogen (Sigma-Aldrich, St Louis, USA), 1:100 000 diluted protein A from test around the log10 scale, assuming geometric mean titre ratios of greater than three, with a one-sided type I error level of 0025 and assuming a SD of 04 in the log10 titres (based on previously published data).29 Only descriptive statistics were used for this interim analysis. one of three primeCboost, chimeric haemagglutinin-based vaccine regimens or one of two placebo groups. The vaccine regimens included a chimeric H8/1, intranasal, live-attenuated vaccine on day 1 followed by a non-adjuvanted, chimeric H5/1, intramuscular, inactivated vaccine on day 85; the same regimen but with the inactivated vaccine being adjuvanted with AS03; and Androsterone an AS03-adjuvanted, chimeric H8/1, intramuscular, inactivated vaccine followed by an AS03-adjuvanted, chimeric H5/1, intramuscular, inactivated vaccine. In this planned interim analysis, the primary endpoints of reactogenicity and safety were assessed by blinded study group. We also assessed anti-H1 haemagglutinin stalk, anti-H2, anti-H9, and anti-H18 IgG antibody titres and plasmablast and memory B-cell responses in peripheral blood. This trial is usually registered with ClinicalTrials.gov, number “type”:”clinical-trial”,”attrs”:”text”:”NCT03300050″,”term_id”:”NCT03300050″NCT03300050. Findings Between Oct 10, 2017, and Nov 27, 2017, 65 participants Androsterone were enrolled and randomly assigned. The adjuvanted inactivated vaccine, but not the live-attenuated vaccine, induced a substantial serum IgG antibody response after the primary immunisation, with a seven occasions increase in anti-H1 stalk antibody titres on day 29. After boost immunisation, all vaccine regimens induced detectable anti-H1 stalk antibody (22C56 occasions induction over baseline), cross-reactive serum IgG antibody, and peripheral blood plasmablast responses. An unsolicited adverse event was reported for 29 (48%) of 61 participants. Solicited local adverse events were reported in 12 (48%) of 25 participants following primary vaccination with intramuscular study product or placebo, in 12 (33%) of 36 after primary immunisation with SDF-5 intranasal study product or placebo, and in 18 (32%) of 56 following booster doses of study product or placebo. Solicited systemic adverse events were reported in 14 (56%) of 25 after primary immunisation with intramuscular study product or placebo, in 22 (61%) of 36 after immunisation with intranasal study product or placebo, and in 21 (38%) of 56 after booster doses of study product or placebo. Disaggregated safety data were not available at the time of this interim analysis. Interpretation The tested chimeric haemagglutinin-based, universal influenza computer virus vaccine regimens elicited cross-reactive serum IgG antibodies that targeted the conserved haemagglutinin stalk domain name. This is the first proof-of-principle study to show that high anti-stalk titres can be induced by a rationally designed vaccine in humans and opens up avenues for further development of universal influenza computer virus vaccines. On the basis of the blinded study group, the vaccine regimens were tolerable and no safety concerns were observed. Funding Bill & Melinda Androsterone Gates Foundation. Introduction Seasonal influenza viruses cause up to 650 000 deaths and 3C5 million severe infections annually worldwide.1 Current vaccines protect well against influenza when they match circulating strains, but must be updated and re-administered annually because of antigenic drift of the virus. Annual strain selection for Androsterone seasonal vaccines is based on predictions, therefore mismatches often occur, leading to a substantial decrease in vaccine effectiveness. Additionally, pandemics occur in irregular intervals causing substantial morbidity and mortality. Matched vaccines have to be manufactured for these emerging viruses, a process that takes about 6 months,2 during which time the population remains vulnerable. A vaccine that protects against influenza independently of antigenic drift or shift is, therefore, urgently needed, as emphasised by the National Institute of Allergy and Infectious Diseases. 3C5 Research in context Evidence before this study PubMed was searched with the terms universal influenza virus vaccine, hemagglutinin stalk, influenza heterosubtypic immunity, and anti-stalk Androsterone antibody, without language restrictions, for literature published between database inception and March 21, 2019. The first paper regarding a broadly protective haemagglutinin stalk-reactive antibody was published in 1993; similar antibodies were then discovered for the first time in humans in 2008. The existence of these antibodies in humans suggested that designing a universal influenza virus vaccine might.