This newly vaccinated subgroup provided the reference for comparison

with other subgroups who were vaccinated for longer periods. Specimens were collected after a signed informed consent was obtained from Docetaxel each participant, and the data collected were handled so as to protect confidentiality. The study protocol was approved by the Research Ethics Committee of the Evandro Chagas Clinical Research Institute at FIOCRUZ (Opinion No. 040/2011). Subjects with proof of vaccination (in vaccination card or medical records) and who agreed to the terms of the study were eligible to participate in the study. Exclusion criteria included the following: contraindications for yellow fever vaccine (e.g., pregnancy, permanent or transient immunosuppression, severe adverse reactions following previous vaccination, and severe allergy to chicken eggs), individuals who reported 2 or more previous vaccine doses (even if proof of vaccination could not be provided), lack of proof of prior vaccination, and residence in or travel to risk areas (which have been defined by the Health Surveillance Department of the Ministry of Health) until the time

of the study. The rationale for inclusion of subjects with a documented single dose of yellow fever vaccine and no potential exposure to natural infections was to avoid interference of booster on antibody levels induced by one dose. Cases with uncertain potential exposure to infection were not included. In addition, military personnel who participated in missions to endemic areas or who had Obeticholic Acid in vivo been immunised more than once were excluded from the study. The yellow fever

neutralising antibody titres were quantified by PRNT50 using 20 μL of heat inactivated (56 °C for 30 min) serum as described by Simões and colleagues [8] in the Laboratory of Viral Technology of Bio-Manguinhos (LATEV/BIO, in Rio de Janeiro). In each set of tests, a standard serum prepared in house was included as positive control (called M7/100). This serum from Rhesus monkeys (Macaca mulatta) vaccinated against YF had been calibrated against an also international reference serum from WHO and was known to contain 1115 IU/mL. Antibody concentration in IU/mL was calculated relative to the antibody content in the international reference (quotient of 1115 IU/mL and the dilution corresponding to the 50% endpoint of the reference is multiplied by the dilution equivalent to the 50% of each serum sample). Yellow fever antibody titres (in IU/mL) were classified as follows: titres ≥2.9 log10 IU/mL or reciprocal of the dilution ≥50 indicated positive serology; titres <2.5 log10 IU/mL or reciprocal of the dilution <5 indicated negative serology; titres ≥ 2.5 and <2.9 log10 IU/mL or reciprocal of the dilution ≥5 and <50 indicated undetermined serology.