But prior to its use in Hepatitis C (and also in hepatitis B), interferon was explored extensively for the treatment of HIV infection. Prior to the availability of potent combination therapy, interferon at fairly high-doses showed some success in treating the cancer Kaposi’s Sarcoma in HIV patients.
Other studies also showed some ability of interferon to lower viral load, especially when combined with other HIV drugs, but not to undetectable levels as we see with the current combination therapies. In the early nineties, there were only a couple of HIV medicines available (AZT/zidovudine, ddI/didanosine) and these were fairly weak and not able to suppress the virus significantly as single drugs.
In addition, they required multiple doses a day and had significant side-effects and toxicities. Other alternatives were desperately sought and studies coming out of Africa at the Kenya Medical Research Institute suggested that low-doses of alpha-interferon taken sublingually (under the tongue) could be effective in HIV disease. In African-American communities, there was a lot of interest in this potential therapy, however, the clinical trials did not show much promise. Combination therapy for HIV disease became available around 1996.
Because of the broad actions of interferons across many types of viruses, it is reasonable to test its effect against COVID-19. Studies are underway.