Microsoft co-founder Bill Gates said Wednesday that people could need multiple doses of a potential coronavirus vaccine to immunize themselves from the coronavirus. If necessary, the multiple doses could require more than 7 billion vaccinations to be administered worldwide.

"None of the vaccines at this point appear like they'll work with a single dose," Gates said. "That was the hope at the very beginning."

The billionaire philanthropist, who has donated $300 million towards the global effort to combat COVID-19 through the Bill & Melinda Gates Foundation, told "CBS Evening News" anchor and managing editor Norah O'Donnell that deploying a coronavirus vaccine will require a global effort.

"If what you're trying to do is block all the transmission, then you need to get 70-80% coverage on a global basis. So it's unbelievably big numbers," he said.

Bill Gates says he receives a 20 to 1 return on his vaccine investments, and that his $10 billion investment has returned $200 billion: