Billionaire philanthropist Melinda Gates think it is likely we will have a widely available coronavirus vaccine in 18 months, she said in an interview with Business Insider.

Healthcare workers should get it first, Gates said, followed by people with underlying health conditions. The US will have to work on a plan to distribute the vaccine fairly, she added, particularly given how the federal government has mishandled the distribution of equipment like masks and protective gear during the pandemic.

“We need to look at, okay, does Mississippi get this vaccine at the same time California gets it and New York gets it?” she said. “We can’t do this game that we’re playing right now where you have 50 different states competing for resources for masks and PPE, that makes zero sense. You need a national strategy that will equitably distribute this vaccine and we first look at the vulnerable populations.”

Gates said there’s a “high likelihood” we will have an effective vaccine in 18 months. While that matches the timeline given by Dr. Anthony Fauci, the nation’s top infectious disease expert, vaccines still face great unknowns in going through clinical testing.

In particular, a vaccine has to be safe enough to administer to millions of healthy people. And it also has to work by either protecting people against becoming infected, or at least lowering the risk of serious disease. Ramping up manufacturing to produce billions of doses is another problem with no easy fix.

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Gates oversees the Bill and Melinda Gates Foundation, which is supporting several ongoing vaccine research projects. While some vaccine candidates have started to be tested in humans, it will take at least several months of testing to determine whether they work.

Even with a vaccine that is safe, effective, and widely produced, the next challenge will be ensuring equitable distribution. Gates pointed to the Vaccine Alliance that’s been around since the 1990s as the type of organization that can help with this.

“We have to make sure that the vaccine is very low priced and that there’s a fund for buying it for everyone, whether you’re in a low, middle, or a high income country,” she said. “And that’s doable.”

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A coronavirus vaccine is of critical importance to halting this pandemic. Gates said society cannot reopen and return to normal until “we get a vaccine at scale.”