The duo were said to have used a plastic bag as a condom because they were feeling too shy to get one outside.
They were treated in hospital for genital lesions, abrasions and bleeding.
Deputy director of Hanoi Kidney Hospital, Doctor Nguyen The Luong, said that the couple were both college students.
Luong added that the pair, who live in Vietnam, have been examined and are on antibiotics to help them recover.
They can cause scratches and vaginal tearing and are not suitable for the protection offered by condoms.
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