Through the Gates Foundation, Bill Gates has spent nearly two decades spreading vaccines around the globe in order to provide protection against deadly conditions " to all the children in the world."

But as more preventable measles outbreaks sprout up in wealthy countries such as the US, France, and Japan, Gates is warning that it's only a matter of time before the anti-vaccine trend turns deadly.

"Unfortunately this will mean some measles or pertussis deaths," Gates said during a Reddit AMA on Monday.

In rich countries around the world, the measles is making a comeback.

The US, which had nearly eradicated the contagious virus by the early 2000s, has logged 159 cases so far in 2019. In Japan, 167 people have already been diagnosed with the measles in the first six weeks of this year — the highest measles-infection rate for the country in more than a decade. And last year, the UK logged more than 900 confirmed measles cases, mainly in unvaccinated kids and teens, while 2,913 people in France got the virus.

"Our data is showing that there is a substantial increase in measles cases. We’re seeing this in all regions," Katherine O’Brien, the World Health Organization's (WHO) director of immunization and vaccines, said earlier this month. "We’re having outbreaks that are protracted, that are sizable, and that are growing."

Public-health officials have been warning for some time now that this is the consequence of people choosing not to vaccinate their children. The WHO said "vaccine hesitancy" is one of the biggest threats to the health of the world.

Some pediatricians in the US have also voiced concerns that relaxed regulation in many states is creating a breeding ground for all kinds of preventable infections, including the measles.

Only three states have medical-only exemptions: California, West Virginia, and Mississippi. Shayanne Gal/Business Insider

Asked for his thoughts on the situation, Bill Gates added his own voice to the growing alarm about anti-vaxxer parents in a Reddit "ask me anything" post on Monday.

"It is surprising to see how in the richer countries the consensus that kids should be protected has been lost," Gates said on Monday. "Unfortunately this will mean some measles or pertussis deaths."

Before the invention of the measles vaccine in 1963, the contagious virus was a ubiquitous childhood illness. Deadly measles complications affected about one in every 1,000 patients who got the measles, and more than 400 people died from measles every year in the US. The country hasn't seen a deadly measles case since 2015, however, when one woman with a compromised immune system died from pneumonia resulting from measles complications.

Still, a growing number of people rely on debunked junk science and other false information to back up their belief that vaccines are dangerous.

"Vaccines have saved more lives than any other tool," Gates said.

Gates administers an oral polio vaccine to Nikunj Kumar, 5, of New Delhi on September 14, 2000. Jeff Christensen/Liaison via Getty Images

Public-health experts around the world say the same.

"We risk losing decades of progress in protecting children and communities against this devastating but entirely preventable disease," Soumya Swaminathan, a deputy director general at WHO, said in a recent statement.

Many of the measles cases in the US this year have popped up in the Pacific Northwest, where at least 57 unvaccinated people have contracted the illness.

"People become complacent because they don't realize how bad it can be," Alan Melnick, the public-health director in Clark County, recently told Business Insider. "And that's what scares me the most."