• Bill Gates wrote in a blog post on Thursday that he considered eight to 10 candidates for a coronavirus vaccine to be promising.
  • The billionaire Microsoft cofounder believes it will take 18 months to develop a vaccine, though he says it could come as soon as nine months or take as long as two years.
  • Alongside candidates that use traditional methods, Gates is particularly excited about two new kinds of vaccine: RNA and DNA vaccines.
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More than 100 coronavirus vaccines are in the works, but eight to 10 have caught the eye of Bill Gates.

The billionaire Microsoft cofounder is pouring hundreds of millions of dollars into developing a vaccine through his philanthropic organization, the Bill & Melinda Gates Foundation. The foundation so far has pledged $250 million toward fighting the novel coronavirus, and Gates recently announced that the organization planned to dedicate its full resources to the pandemic.

Gates published a blog post on Thursday laying out the process for developing and distributing a vaccine. He wrote that a vaccine was likely to take about 18 months to develop, though he added that it “could be as little as 9 months or as long as two years.”

Read more: Here’s how 13 top drugmakers are sprinting to develop a coronavirus vaccine or treatment that can halt this pandemic

"As of April 9, there are 115 different COVID-19 vaccine candidates in the development pipeline," Gates wrote. "I think that eight to ten of those look particularly promising. (Our foundation is going to keep an eye on all the others to see if we missed any that have some positive characteristics, though.)"

Gates said the promising candidates "take a variety of approaches to protecting the body against COVID-19," going on to explain how there are two main kinds of vaccine: inactivated and live.

Inactivated vaccines contain a dead version of the desired pathogen, whereas live ones contain a smaller but living dose of it. Gates described these methods as traditional and reliable but added that they were resource-intensive and slow to develop.

"I'm particularly excited by two new approaches that some of the candidates are taking: RNA and DNA vaccines," Gates wrote.

"Rather than injecting a pathogen's antigen into your body, you instead give the body the genetic code needed to produce that antigen itself. When the antigens appear on the outside of your cells, your immune system attacks them - and learns how to defeat future intruders in the process. You essentially turn your body into its own vaccine manufacturing unit."

Though the Gates Foundation has been researching RNA vaccines for almost a decade, they are yet to make it out into the wild. "Since COVID would be the first RNA vaccine out of the gate, we have to prove both that the platform itself works and that it creates immunity," Gates said. "It's a bit like building your computer system and your first piece of software at the same time."

A key challenge around producing a vaccine for COVID-19 is that a coronavirus vaccine has never been developed to date.

Read more: There are more than 70 potential coronavirus vaccines in the works. Here are the top efforts to watch, including the 16 vaccines set to be tested in people this year.

But the Microsoft billionaire has said numerous times that a return to total normality is impossible without a vaccine.

"Humankind has never had a more urgent task than creating broad immunity for coronavirus," he wrote. "Realistically, if we're going to return to normal, we need to develop a safe, effective vaccine."