Pharmaceutical manufacturer Pfizer is hopeful that an oral treatment it has developed for COVID-19, which began early stage clinical trials in March, could be approved for use in the United States by the end of this year. The drug is a protease inhibitor which stops viral replication and is based on treatments for other viruses such as hepatitis C and HIV. Researchers hope that the drug can slow disease progression if taken at symptom onset and reduce severe cases of the disease.