Inclusion/Exclusion Criteria

The inclusion criteria for both groups comprised: individuals > 18 years, able to understand and read the consent form, or have a legal representative to read it, and had never received YF vaccination. Moreover, in the AID group, each patient fulfilled international classification criteria for AID, according to the American College of Rheumatology and/or European League Against Rheumatism international classification criteria for RA, SpA, SSC, SLE, and SS (18–23). All patients were advised by a rheumatologist to undergo planned YF vaccination when in remission or had low disease activity; and, when using immunosuppressant or biological therapy were advised that it was safe to interrupt this by their physician. The interval between withdrawal of therapy and YF vaccination was that specified in the Brazilian Recommendations for YF vaccination in patients with AID (17), as follows: interval > 3 months for immunosuppressive oral therapy, > 5.5 half-lives for any biological therapy, and ≥ 6 months for rituximab (Table 1) (6, 17, 24, 25).

Minimum period of time recommended between withdrawal of therapy and 17DD-YF vaccination for patients with AID, according to Brazilian recommendations ^a.

Exclusion criteria comprised: patients who had not been advised by a rheumatologist to receive the vaccine; did not agree to participate; immunosuppressed by other causes (HIV carriers with CD4 count <200 cells/mm³ or lymphocytes <500 cells/mm³); low IgG or IgM levels; organ transplantation history; primary immunodeficiency; neoplasia; previous history of thymus diseases (myasthenia gravis, thymoma, thymus absence, or surgical removal); high disease activity index; receiving high levels of immunosuppressive treatment with cyclophosphamide, mycophenolate mofetil, tacrolimus, cyclosporine, sirolimus, azathioprine > 2 mg/kg/day, prednisone ≥ 20 mg/day, methotrexate > 20 mg/week, or any immunobiological drug (17, 24, 25); and received another vaccine simultaneously or at an interval <30 days. Individuals previously vaccinated against YF, according to their medical records, and those with seropositive results for anti-YF antibody by plaque reduction neutralization test (PRNT ≥ 1:50 at baseline) were also excluded.