The United States government has ordered 300 million doses of a potential COVID-19 vaccine being developed by AstraZeneca and Oxford University and hopes first doses can be made available by October, the Department of Health and Human Services said on Thursday.

"This contract with AstraZeneca is a major milestone in Operation Warp Speed's work toward a safe, effective, widely available vaccine by 2021," HHS Secretary Alex Azar said in a statement.

The U.S. is the world's worst affected country by the COVID-19 pandemic, having reported more than 1.5 million infections with over 93,000 deaths, according to the Johns Hopkins University.

Globally, the disease has infected more than 5 million people, with a death toll exceeding 329,000.