HIV infection remains a global public health challenge, reinforcing the importance of developing preventive vaccines. However, vaccine-induced seroreactivity (VISP/R) compromises the accuracy of current diagnostic tests, which do not distinguish between vaccine-induced antibodies and those produced by natural infection. This study aims to analyze the dynamics of HIV diagnostic tests used in public health services for the follow-up of individuals with VISP after participation in clinical trials.

Longitudinal study with chart review of individuals vaccinated experimentally against HIV, using or not using pre-exposure prophylaxis (oral PrEP), followed in a public health service and undergoing regular tests such as serology, immunoblot and HIV RNA PCR. Follow-up took place from January 2023 to April 2025. Data were recorded in REDCap, analyzed in STATA/MP 19, and Wilcoxon and Mann-Whitney tests were used for statistical analysis.

Thirty-eight individuals were followed after completion of the clinical trial: 61% white, mean age 37 years, all cisgender men, 89% men who have sex with men (MSM) and 87% with schooling ≥8 years. PrEP use was reported by 74%, predominantly in the daily regimen (88%), with a mean use of 2.65 years. During the period, 173 samples were collected, with 172 HIV RNA PCR results undetectable and one result with 25 copies, later confirmed as false positive after diagnostic investigation. Serologic tests were positive in 97.68% of samples. Two serologic kits were used (Architect® HIV Ag/Ab Combo and Vitros® HIV Combo), with higher median values for Vitros (45.0 vs. 20.7; p<0.001). Among the 168 immunoblots (DPP HIV 1 and 2 Bio-Manguinhos rapid immunoblot), 36% of samples were reactive for all bands. The GP120, GP41, GP160 and p24 bands showed positivity in 88%, 80%, 73% and 41% of samples, respectively, with 87% of tests reactive and 13% indeterminate.

The persistence of VISP/R after the end of the vaccine trial highlights the limitation of current diagnostic tests in distinguishing vaccine-induced immune response from HIV infection. These findings reinforce the need for diagnostic methods with greater specificity and feasibility for large-scale use in public services, promoting greater autonomy for individuals in choosing their care sites and preventing stigmatization associated with false-positive results.