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Influenza is a major medically attended respiratory illness. The impact of influenza on morbidity and mortality is particularly high in the elderly. Immunosenescence attenuates the immune response of influenza vaccine in the elderly. High-dose influenza vaccine contains 60 μg of hemagglutinin per strain, four times more compared with standard-dose (SD) influenza vaccine. This study is a phase I clinical trial investigating the immunogenicity and safety of the GC3114, high-dose, quadrivalent inactivated influenza vaccine (HD-QIV) in healthy adults aged 19-64 years during the 2017-2018 season. Seroprotection rates of HD-QIV were 100.0% for A/H1N1, 96.67% for A/H3N2, 83.33% for B/Yamagata, and 96.67% for B/Victoria. Seroconversion rate for A/H1N1, A/H3N2, B/Yamagata, and B/Victoria strains were 86.67%, 90.0%, 53.33%, and 53.33%, respectively, in the HD-QIV group. The post-/pre-vaccination geometric mean titer ratio (GMTR) was 15.28 for A/H1N1, 8.19 for A/H3N2, 3.56 for B/Yamagata, and 3.03 for B/Victoria in the HD-QIV group. Seroconversion rate and post-/pre-vaccination GMTR for A/H3N2 were significantly higher in the HD-QIV group than in the SD-QIV group (control). No serious adverse events were reported. In conclusion, GC3114 was safe, well-tolerated, and immunogenic in healthy adults. Clinical Trials Identifier: NCT03357263., (Copyright © 2019. Published by Elsevier Ltd.)

Influenza virus is a common pathogen implicated in respiratory tract infections, annually affecting up to 20% of the general population, and pneumonia is a leading cause of death after influenza infection. Post-influenza pneumonia is especially common in the elderly and chronically ill patients. The risk of post-influenza pneumonia is significantly increased according to the number of concurrent comorbidities. Vaccination is the primary measure used to abate influenza epidemics and associated complications. In meta-analyses, influenza vaccine significantly reduces pneumonia- and influenza-related hospitalizations, with a vaccine effectiveness of 25-53%. However, considering the poor effectiveness of conventional influenza vaccines in the elderly, several highly immunogenic influenza vaccines have been developed. Further evaluations of the comparative effectiveness of diverse vaccine formulations are warranted to assess their utility for preventing influenza infection, post-influenza pneumonia, and related hospitalization/mortality. Based on cost-effectiveness and budget impact analysis, influenza vaccination strategies should be tailored in the elderly.

Pregnant women are prioritized to receive influenza vaccination. However, the maternal influenza vaccination rate has been low in Korea. To identify potential barriers for the vaccination of pregnant women against influenza, a survey using a questionnaire on the perceptions and attitudes about maternal influenza vaccination was applied to Korean obstetricians between May and August of 2014. A total of 473 respondents participated in the survey. Most respondents (94.8%, 442/466) recognized that influenza vaccination was required for pregnant women. In addition, 92.8% (410/442) respondents knew that the incidence of adverse events following influenza vaccination is not different between pregnant and non-pregnant women. However, 26.5% (124/468) obstetricians strongly recommended influenza vaccination to pregnant women. The concern about adverse events following influenza vaccination was considered as a major barrier for the promotion of maternal influenza vaccination by healthcare providers. Providing professional information and education about maternal influenza vaccination will enhance the perception of obstetricians about influenza vaccination to pregnant women and will be helpful to improve maternal influenza vaccination coverage in Korea.