Use of Pfizer Inc's COVID-19 oral antiviral treatment Paxlovid has jumped 315% over the past four weeks, the U.S. Department of Health and Human Services said on Tuesday.

Nearly 115,000 courses of the pills were dispensed during the first week of May, a senior health official said. A total of 668,954 courses out of the more than 2 million ordered by pharmacies were administered overall.

"In recent weeks we've gone from 20,000 sites with Paxlovid to approximately 35,000 and we'll keep working to increase availability," the official told reporters on a call.

Paxlovid is approved to keep high-risk individuals with COVID-19 from becoming seriously ill. It is meant to taken for five days beginning shortly after symptom onset.

Pharmacies ordered almost 1.8 million courses of Merck & Co's rival oral antiviral, molnupiravir, and 230,257 have been administered so far, the official added.

The department, alongside the U.S. postal services, has shipped around 360 million coronavirus tests to homes nationwide, the official said.