The company's stock surged by more than 4 percent on the news.
Three U.S. companies are currently in Phase 3 clinical trials of vaccines and are on pace to develop one before the end of the year. The country expects 500 million doses to be available before Dec. 31, Trump said during a news conference.
"Today’s announcement puts another building block in place as the nation moves toward a safe and effective COVID-19 vaccine," Centers for Disease Control and Prevention Director Dr. Robert Redfield said in a statement. "America’s march toward one or more safe and effective COVID-19 vaccines is a combined effort between American industry and the federal government."
"McKesson is committed to supporting public health in the U.S. and around the world," CEO Brian Tyler said in a statement. "Since the onset of the pandemic, McKesson has leveraged our deep expertise to help maintain the integrity of the healthcare supply chain, source and distribute personal protective equipment to frontline workers and stand up COVID-19 testing."
The CDC awarded an existing contract to McKesson in 2016 to help distribute vaccines in the event of a pandemic.