title: Vaccinated students with negative enzyme immunoassay results show positive measles virus-specific antibody levels by immunofluorescence and plaque neutralisation tests.
abstract: BACKGROUND
  The prevalence of measles antibodies was investigated by an enzyme immunoassay (EIA) in students aged 14 every year since 1996 in a Swiss municipality. This region has wide measles vaccine coverage (first dose > or = 95%, second dose > or = 65%) without any reported measles outbreaks since 20 years. In 2003 and 2004, in contrast to previous years, surprisingly many negative results (33% and 54%, respectively) were observed.
  
  
  OBJECTIVE
  To corroborate the measles antibody values by different methods.
  
  
  METHODS
  Serum samples from 101 students with known vaccination status were available. Sera with equivocal and negative results obtained by two different EIAs were retested by indirect immunofluorescence test (IFT) and plaque neutralisation test (PNT).
  
  
  RESULTS
  Retesting by IFT showed a positive result in 17/21 sera (81%) and retesting by PNT indicated that 46/49 sera (94%) were positive; the three sera with negative PNT result were from unvaccinated individuals. Only 3/96 vaccinated students showed measles antibodies below the putative protective level of 0.2 IU/ml after retesting by PNT.
  
  
  CONCLUSIONS
  Negative EIA results should be interpreted with caution in a widely vaccinated population without booster by circulation of wild viruses. Retesting by IFT or PNT is recommended.
authors.affiliation: National Reference Centre Measles, Mumps, Rubella, Robert Koch Institute, Berlin, Germany. tischera@rki.de
authors.forename: Annedore
authors.initials: A
authors.lastname: Tischer
authors.forename: Markus
authors.initials: M
authors.lastname: Gassner
authors.forename: Jean-Luc
authors.initials: JL
authors.lastname: Richard
authors.forename: Franziska
authors.initials: F
authors.lastname: Suter-Riniker
authors.forename: Annette
authors.initials: A
authors.lastname: Mankertz
authors.forename: Ulrich
authors.initials: U
authors.lastname: Heininger
mesh_terms: D000293:Adolescent; D000918:Antibody Specificity; D005260:Female; D005455:Fluorescent Antibody Technique; D006801:Humans; D007124:Immunoenzyme Techniques; D007074:Immunoglobulin G / Q000096:biosynthesis / Q000097:blood*; D008297:Male; D008457:Measles / Q000453:epidemiology / Q000276:immunology / Q000517:prevention & control*; D022542:Measles-Mumps-Rubella Vaccine / Q000276:immunology* / Q000627:therapeutic use; D009500:Neutralization Tests; D016036:Seroepidemiologic Studies; D013557:Switzerland / Q000453:epidemiology
chemical_list: D007074:Immunoglobulin G; D022542:Measles-Mumps-Rubella Vaccine