Immunogenicity and Safety of Intradermal Trivalent Influenza Vaccination in Nursing Home Older Adults: A Randomized Controlled Trial

Abstract

ObjectiveTo compare the immunogenicity and safety between full-dose (15 μg) intramuscular (IM) and full-dose (15 μg) intradermal (ID) immunization of the trivalent influenza vaccine in nursing home older adults. DesignA single-center, randomized, controlled, open-label, parallel group trial from October 2013 to April 2014. SettingNine nursing homes in Hong Kong. ParticipantsHundred nursing home older adults (mean age: 82.9 ± 7.4 years). InterventionFifty received ID (Intanza) and 50 received IM (Vaxigrip) vaccination. MeasurementsBaseline measurements included demographics, comorbidity, frailty and nutritional status. Day 21 and day 180 immunogenicity (seroconversion rate, seroprotection rate, geometric mean titer [GMT] fold increase in antibody titer) using hemagglutination-inhibition and adverse events were measured. Noninferiority and superiority of ID compared with IM vaccination in immunogenicity were analyzed. The study was registered on ClinicalTrials.gov; identifier: NCT 01967368. ResultsAt day 21, noninferiority in immunogenicity of the ID vaccination was demonstrated. The seroconversion rate of the H1N1 strain was significantly higher in the ID group. At day 180, immunogenicity of both groups fell but the GMT of all strains in ID group was higher and the difference was significant for H3N2 strain. The seroconversion rate and GMT fold increase of H3N2 strain was significantly higher in the ID group. Local adverse events was significantly more in ID group, but they were mild and resolved in 72 hours. ConclusionsID vaccination is noninferior, and even superior in some parts of immunogenicity assessment, to IM vaccination without compromising safety in nursing home older adults. ID vaccination is a good alternative to IM vaccination in this population.