Association between antibody titers and protection against influenza virus infection within households

J Infect Dis. 2014 Sep 1;210(5):684-92. doi: 10.1093/infdis/jiu186. Epub 2014 Mar 26.


Background: Previous studies have established that antibody titer measured by the hemagglutination-inhibiting (HAI) assay is correlated with protection against influenza virus infection, with an HAI titer of 1:40 generally associated with 50% protection.

Methods: We recruited index cases with confirmed influenza virus infection from outpatient clinics, and followed up their household contacts for 7-10 days to identify secondary infections. Serum samples collected from a subset of household contacts were tested by HAI and microneutralization (MN) assays against prevalent influenza viruses. We analyzed the data using an individual hazard-based transmission model that adjusted for age and vaccination history.

Results: Compared to a reference group with antibody titers <1:10, we found that HAI titers of 1:40 against influenza A(H1N1) and A(H3N2) were associated with 31% (95% confidence interval [CI], 13%-46%) and 31% (CI, 1%-53%) protection against polymerase chain reaction (PCR)-confirmed A(H1N1) and A(H3N2) virus infection, respectively, while an MN titer of 1:40 against A(H3N2) was associated with 49% (95% CI, 7%-81%) protection against PCR-confirmed A(H3N2) virus infection.

Conclusions: An HAI titer of 1:40 was associated with substantially less than 50% protection against PCR-confirmed influenza virus infection within households, perhaps because of exposures of greater duration or intensity in that confined setting.

Keywords: antibody; immunity; influenza; transmission.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Aged, 80 and over
  • Antibodies, Viral / blood*
  • Child
  • Child, Preschool
  • Family Characteristics*
  • Family Health
  • Female
  • Hemagglutination Inhibition Tests
  • Humans
  • Infant
  • Influenza, Human / immunology*
  • Influenza, Human / prevention & control*
  • Influenza, Human / transmission
  • Male
  • Middle Aged
  • Neutralization Tests
  • Orthomyxoviridae / genetics
  • Orthomyxoviridae / immunology*
  • Orthomyxoviridae / isolation & purification
  • Polymerase Chain Reaction
  • RNA, Viral / genetics
  • Young Adult


  • Antibodies, Viral
  • RNA, Viral