Immunogenicity, Safety, and Efficacy of a Standalone Universal Influenza Vaccine, FLU-v, in Healthy Adults

Background: FLU-v is a broad-spectrum influenza vaccine that induces antibodies and cell-mediated immunity.

Objective: To compare the safety, immunogenicity, and exploratory efficacy of different formulations and dosing regimens of FLU-v versus placebo.

Design: Randomized, double-blind, placebo-controlled, single-center phase 2b clinical trial. (ClinicalTrials.gov: NCT02962908; Eudra CT: 2015-001932-38)

Setting: The Netherlands.

Participants: 175 healthy adults aged 18 to 60 years.

Intervention: 0.5-mL subcutaneous injection of 500 mu g of adjuvanted (1 dose) or nonadjuvanted (2 doses) FLU-v (A-FLU-v or NA-FLU-v) or adjuvanted or nonadjuvanted placebo (A-placebo or NA-placebo) (2:2:1:1 ratio).

Measurements: Vaccine-specific cellular responses at days 0, 42, and 180 were assessed via flow cytometry and enzyme-linked immunosorbent assay. Solicited information on adverse events (AEs) was collected for 21 days after vaccination. Unsolicited information on AEs was collected throughout the study.

Results: The AEs with the highest incidence were mild to moderate injection site reactions. The difference between A-FLU-v and A-placebo in the median fold increase in secreted interferon-gamma (IFN-gamma) was 38.2-fold (95% CI, 4.7- to 69.7-fold; P = 0.001) at day 42 and 25.0-fold (CI, 5.7- to 50.9-fold; P <0.001) at day 180. The differences between A-FLU-v and A-placebo in median fold increase at day 42 were 4.5-fold (CI, 2.3- to 9.8-fold; P <0.001) for IFN-gamma-producing CD4+ T cells, 4.9-fold (CI, 1.3- to 40.0-fold; P <0.001) for tumor necrosis factor-alpha (TNF-alpha), 7.0-fold (CI, 3.5- to 18.0-fold; P <0.001) for interleukin-2 (IL-2), and 1.7-fold (CI, 0.1- to 4.0-fold; P = 0.004) for CD107a. At day 180, differences were 2.1-fold (CI, 0.0- to 6.0-fold; P = 0.030) for IFN-gamma and 5.7-fold (CI, 2.0- to 15.0-fold; P <0.001) for IL-2, with no difference for TNF-alpha or CD107a. No differences were seen between NA-FLU-v and NA-placebo.

Limitation: The study was not powered to evaluate vaccine efficacy against influenza infection.

Conclusion: Adjuvanted FLU-v is immunogenic and merits phase 3 development to explore efficacy.

Primary Funding Source: SEEK and the European Commission Directorate-General for Research and Innovation, European Member States within the UNISEC (Universal Influenza Vaccines Secured) project.