When a person with HIV gets another type, or strain, of the virus it is called HIV superinfection. The new strain of HIV can replace the original strain or remain along with the original strain. Superinfection may cause some people to get sicker faster because the new strain of the virus is resistant to the medicine (antiretroviral therapy or ART) they’re taking to treat the original strain. Hard-to-treat superinfection is rare. Taking medicine to treat HIV can help protect someone from getting a superinfection. If you and your partner have HIV and keep an undetectable viral load, you will not transmit HIV to each other through sex.