Bill Gates says he believes there will be a coronavirus vaccine approved by the US Food and Drug Administration (FDA) by early 2021.

In an interview with Fortune, the Microsoft co-founder says there is a new level of collaboration among drugmakers that could see an immunization receive an emergency use authorization license in the next few months.

'The likelihood is that at least two, three, or four [vaccines] will probably prove to be both safe and efficacious,' he said.

However, anti-vaxx groups fear an inoculation will lead to mandatory jabs while other Americans are skeptical that the FDA is under political pressure to authorize a vaccine before the November 3 presidential election.

Gates says it will depend on how many people receive the shot, and continue to wear masks in the meantime, to determine how quickly the pandemic, which has killed almost 200,000 Americans, is finally over. 

There are more than 170 coronavirus vaccine candidates in various stages of development around the globe, according to the World Health Organization.

At least nine are currently in large-scale trials in humans to prove the jabs are both safe and effective. 

Gates says there are currently six that the Bill & Melinda Gates Foundation see as likely to report positive results in Phase III trials and apply for authorization by the FDA.

But the next hurdle will be scaling up production so that hundreds of millions of doses are ready for distribution.

'We'll be faced with the challenge of scaling up manufacturing to a completely unheard-of level,' Gates said.

'The form of cooperation that's never been done before is having a company that did not invent the vaccine provide its factories so that they can scale up that manufacture.