On October 21, the Centers for Disease Control and Prevention (CDC) issued a warning for HIV-positive people concerning the H1N1 virus, the Dallas Voice reports.

According to the warning, H1N1 in people with low CD4 counts is expected to progress rapidly and be complicated by secondary bacterial infections such as pneumonia. Otherwise, the agency said, positive people “would be expected to present with typical acute respiratory illness and fever or feverishness, headache and muscle aches.”

“Persons with HIV infection should remain vigilant for the signs and symptoms of influenza,” the CDC warns.

While the H1N1 vaccine is available as a nasal mist, that form is made with an altered, live version of the virus, which could be dangerous to those with compromised immune systems. Experts advise HIV-positive people to wait for the injectable vaccine to become available.