The Drug Administration of Vietnam said the fake product is labelled YEZTUGO (lenacapavir) injection and falsely claims to be manufactured by Gilead Sciences.
Authorities said the product has not been granted marketing authorisation in Vietnam and neither the drug nor the listed manufacturer has any approved products registered for circulation in the country.
A local firm, SNB-REACT Vietnam Co., Ltd., also reported suspected trading of counterfeit HIV prevention drugs bearing Gilead branding.
Health officials warned that the fake injection could undermine treatment and pose serious risks to public health. Authorities in Ho Chi Minh City have been asked to verify the case, while health departments nationwide have been instructed to issue warnings.
Local authorities have been urged to strengthen inspections, crack down on violations and coordinate efforts to trace the origin of the counterfeit product and prevent further distribution.
The regulator also called for stricter enforcement against smuggling, trade fraud and intellectual property violations in the healthcare sector.
The public has been advised to use only authorised medicines with clear origins and to report any suspected counterfeit or unlicensed drugs.
Separately, the agency revoked marketing authorisations for 17 medicines at the request of registrants, with existing stocks allowed to be used until expiry.