Immunogenicity and Safety of Half Dose Intradermal Injection Compared to Full Dose Intramuscular Injection of Influenza Vaccine in Healthy Adults

Jo, Yu Mi; Ki, Se Yoon; Song, Joon Young; Choi, Won Suk; Kim, Jeong Yeon; Seo, Yu Bin; Jeong, Hye Won; Kim, Woo Joo; Cheong, Hee Jin; Kim, Sung Ran; Hwang, In Suk

Abstract

BACKGROUND: Influenza is the representative respiratory infectious disease causing significant high morbidity. Vaccination is the most effective method to prevent influenza. To cope with both unstable supply and increasing demand of influenza vaccine with more flexibility, we studied the safety and immunogenicity of half dose intradermal injection of influenza vaccine in healthy adults compared with full dose intramuscular injection method.
MATERIALS AND METHODS
We conducted a randomized, open-label trial in healthy adults of age 15 to 64 years. Subjects were randomly assigned to receive either a recommended dose of influenza vaccine (Fluarix(R), Injection Prefilled Syringe, GlaxoSmithKline, hemagglutinin antigen (HA) 15 microgram) via intramuscular route (designated as control group) or a half recommended dose (HA 7.5 microgram) via intradermal route (designated as experimental group). Blood samplings were done before and more than 28 days after vaccination. We measured the changes in hemagglutination-inhibition (HAI) antibody titers and compared geometric mean titers, seroconversion rates, seroconversion factors and seroprotection rates of each group. Local and systemic adverse events were assessed after vaccination.
RESULTS
In antibody titer against all three antigens (A/H1N1, A/H3N2, B) was more evident in intramuscular injection group but intradermal group with half dose showed acceptable immunogenicity fulfilling criteria for Committee for Proprietary Medicinal Products (CPMP). Likewise, seroprotection rates for all three viral strains showed no significant difference between the two groups. Although local reactions were significantly more frequent and lengthy in intradermal group than in intramuscular group, the reactions were mild and transient.
CONCLUSION
Compared with intramuscular injection of full dose influenza vaccine, intradermal injection of half dose resulted in comparable immunogenicity in healthy adults. Intradermal administration of half dose influenza vaccine could be a practical alternative plan to expand the supplies of influenza vaccine, but further studies will be needed in high risk groups.