Diagnosing HIV‐1 infection as early as the primary infection is crucial. In this context, we performed a comparative evaluation and agreement analysis of the newly proposed serological assay for the combined detection of total antibodies against HIV and P24 antigen (HIV VIDAS® DUO AG/AB, bioMérieux®), with the previously available HIV VIDAS® DUO Ultra assay in the well characterized acute‐HIV‐infection multicentric ANRS‐CO‐06‐PRIMO Cohort in classification of Fiebig stages combined with confirmatory testing. Samples collected on the day of enrollment in the cohort, between April 2024 and June 2025, were analyzed with both serological assays. We also performed a recency infection assay, an HIV‐1 westernblotting and the measurement of HIV‐RNA. Acute infection was classified according to Fiebig stages and compared between both assays. All samples (n = 77) were positive with both assays. One major discordance was noted, with a positive antigen and a negative antibody reaction with DUO AG/AB, with an opposite configuration with DUO Ultra. A high proportion of not determinable signals (26% to 68%) was noted with both assays, prompting a difficulty in classifying acute infection stages in the absence of confirmatory assays. The high rate of not determinable signals especially with P24 antigen with both assays demonstrated in our study, could prompt a difficulty in acute infection classification according to Fiebig.
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