Assessment of IgG antibodies against yellow fever virus after vaccination with 17D by different assays: neutralization test, haemagglutination inhibition test, immunofluorescence assay and ELISA.

We analysed serum samples of 209 subjects immunized with yellow fever vaccine 17D by different assays: neutralization test, immunofluorescence assay, haemagglutination inhibition test and ELISA, for presence of 17D-specific antibodies. Serum samples were taken from a few weeks up to 35 years after vaccination. The neutralization test had the highest sensitivity. There was no correlation of results between the serological assays. Considering NT titres > 1:10 as indicating protection, we found that about 75% of subjects remained immune even 10 years after vaccination, with a median NT titre of 1:40 in reactive sera.