title: Long-term immunogenicity of the influenza vaccine at reduced intradermal and full intramuscular doses among healthy young adults.
abstract: OBJECTIVE
  To prepare for vaccine shortages under an influenza pandemic, several antigen-sparing strategies have been investigated. This study was aimed to evaluate the immunogenicity of influenza vaccine at reduced intradermal and full intramuscular dose.
  
  
  METHODS
  We compared the effect of one-fifth and one-half intradermal doses to the full intramuscular dose on immunogenicity in healthy young adults, using a commercial influenza vaccine. A hemagglutination inhibition assay was used to compare the immunogenicity of the vaccination methods.
  
  
  RESULTS
  The one-fifth intradermal dose (3 µg hemagglutinin antigen, HA) was given to 30 participants, the one-half intradermal dose (7.5 µg HA) was given to 30, and the full intramuscular dose (15 µg HA) was given to 32. No significant differences among injection routes and dosages were seen for seroprotection rate, seroconversion rate, or geometric mean titer (GMT) fold-increase for A/H1N1, A/H3N2, and B at around 4 weeks from vaccination. Although GMT for influenza B was significantly lower at six months for the one-fifth intradermal vaccination compared to the full-dose intramuscular vaccination (32.8 vs. 63.2, p=0.048), all three groups met the Evaluation of Medicinal Products (EMA) immunogenicity criteria through 1 to 6 months.
  
  
  CONCLUSIONS
  Intradermal administration of a one-fifth dose of influenza vaccine elicited antibody responses comparable to the intradermal one-half dose and a conventional intramuscular vaccination at 1 month post-vaccination. The immunogenicity of the one-fifth intradermal dose was sufficient to meet the requirement for the EMA criteria at six months after influenza vaccination.
authors.affiliation: Division of Infectious Diseases, Department of Internal Medicine, Korea University College of Medicine, Seoul, Korea. ; Asian Pacific Influenza Institute, Korea University College of Medicine, Seoul, Korea.
authors.forename: Joon Young
authors.initials: JY
authors.lastname: Song
authors.forename: Hee Jin
authors.initials: HJ
authors.lastname: Cheong
authors.forename: Ji Yun
authors.initials: JY
authors.lastname: Noh
authors.forename: Tae Un
authors.initials: TU
authors.lastname: Yang
authors.forename: Yu Bin
authors.initials: YB
authors.lastname: Seo
authors.forename: Kyung-Wook
authors.initials: KW
authors.lastname: Hong
authors.forename: In Seon
authors.initials: IS
authors.lastname: Kim
authors.forename: Won Suk
authors.initials: WS
authors.lastname: Choi
authors.forename: Woo Joo
authors.initials: WJ
authors.lastname: Kim
keywords: Adult; Immunogenicity; Influenza vaccines; Intradermal injections; Vaccines