On Saturday, multi-billionaire and philanthropist Bill Gates sent out a celebratory tweet to let people know that the global vaccination rates are at their highest point in history and that such a feat has economic benefits in addition to humanitarian ones. 

“For every $1 spent on childhood vaccines, you get $44 in benefits,” Gates wrote in the tweet, before linking to a post on his blog where he explains that that figure includes the money a family saves when they do not have to take off work to take off an ailing child.

The Microsoft co-founder's post comes in the wake of a press conference earlier this week where actor Robert DeNiro and activist Robert F. Kennedy Jr. announced a $100,000 award for anyone who can prove vaccine safety.

Gates has made one of his primary philanthropic crusades spreading vaccines around the world to stop preventable deaths. Partially as a result, in 2015, the vaccination gap between low-income and high-income nations hit its lowest level in modern history with a 16 percent discrepancy between the two. In 2000, the gap was more than 40 percent.

As always, however, there is more work to be done. In a post of their own released on Tuesday, UNICEF said that 1.5 million children die annually from diseases that could be prevented by vaccinations. These children are almost always from low-income countries.

At the end of their annual letter, Bill and Melinda Gates ended with some advice:

“People ask us all the time how they can help in the fight against child mortality–and we are always proud to recommend making a donation to UNICEF, an organization that is successful at serving families and children worldwide. We hope your gift will help inspire others to get involved as well.”