Asymptomatic Human Infections With Avian Influenza A(H5N1) Virus Confirmed by Molecular and Serologic Testing

Have asymptomatic infections with highly pathogenic avian influenza A(H5N1) virus been reported in humans?This scoping review of published reports through August 25, 2025, identified 10 reports of 18 cases of asymptomatic infection with A(H5N1) virus, including 2 cases with molecular and serologic confirmation and 16 cases with molecular confirmation alone. Symptom ascertainment methods varied among reported cases.Asymptomatic human avian influenza A(H5N1) virus infections have been infrequently reported, with most lacking serologic confirmation; prospective surveillance studies with serial respiratory and serum sampling and detailed symptom monitoring for persons with high-risk exposures could provide data to inform future public health responses.

Corresponding Author: Fatimah S. Dawood, MD, 2024 Influenza A(H5N1) Response, Centers for Disease Control and Prevention, 1600 Clifton Rd, MS A32, Atlanta, GA 30329 (fdawood@cdc.gov).

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