Evaluation Of Immunogenicity And Safety Of 2009 A/H₁N₁ Influenza Virus Vaccine Based On Real-Time Cell-based Analysis （RTCA） System

ObjectivesThe purpose of the study is to verify whether Real-Time Cell-based Analysis (RTCA) System can be used for measuring neutralization antibody, and to evaluate the immunogenicity and safety of a monovalent, unadjuvanted inactivated 2009 A/H1N1 influenza vaccine.MethodsWe conducted an observational clinical trial to evaluate the immunogenicity and safety of a licensed 2009 A/H1N1 influenza virus vaccine. The study verified whether Real-Time Cell-based Analysis (RTCA) System can be used for dynamic monitoring of influenza virus-mediated cytopathogenic effect (CPE) and measuring of neutralization antibody titers. The results of neutralization assays (NA) based on RTCA system and hemagglutinin-inhibition assays (HA) were analyzed and compared in the coincidence rate and relevance. On this basis, we measured antibody titers by means of hemagglutinin- inhibition assays and neutralization assays based on RTCA system at baseline,7days and 21 days after vaccination. The coprimary immunogenicity end points were the proportion of subjects with antibody titers of 1:40 or more on hemagglutination-inhibition assay, the proportion of subjects with antibody titers of 1:160 or more on neutralization assays based on RTCA system, the proportion of subjects with either seroconversion or a significant increase in antibody titer, the geometric mean titer (GMT) and the factor increase in GMT. All adverse events were noted and analyzed in incidence and intensity.ResultsThe study confirmed that RTCA system can dynamically monitor the CPE on MDCK cells infected with influenza virus. The coincidence rates of hemagglutinin-inhibition assays and neutralization assays based on RTCA system were 70.0% and 65.0% on days 7 and 21 after vaccination, respectively. A linear regression relationship was showed between hemagglutinin-inhibition assays and neutralization assays based on RTCA system (R0d2=0.8213, P<0.0001; R7d2=0.6676, P<0.0001). Antibody titers gradually increased after vaccination. By days 21 after vaccination, hemagglutinin- inhibition antibody titers of 1:40 or more and neutralization antibody titers of 1:160 or more were achieved in 82.1%(101/123) and 100% of subjects, respectively. The geometric mean titer (GMT) respectively increased to 1:95.27 and 1:525.44. Moreover, the rates of seroconversion, as measured using hemagglutinin-inhibition assays and neutralization assays, were 73.98% and 91.87%, respectively. Adverse events were observed in 49 of 136 subjects (36.0%), of which local discomfort and systemic symptoms were respectively reported by 19.1% and 22.1% of subjects. Injection site pain (14.0%) and fatigue (12.5%) respectively were the most common local discomfort and systemic symptoms. All adverse events were mild to moderate in intensity, without any deaths or serious events.ConclusionsThese data suggest that the RTCA system can be used for measuring neutralization antibody and a single dose of monovalent inactivated 2009 A/H1N1 influenza virus vaccine, containing 15μg of hemagglutinin antigen induces a typically protective immune response in the majority of subjects between 18 and 60 years old. The vaccine was well tolerated, with mild to moderate vaccine-associated adverse events. (ClinicalTrials.gov number, NCT01055990)...