Invisible Ink Could Reveal whether Kids Have Been Vaccinated 

".....The work was funded by the Bill & Melinda Gates Foundation and came about because of a direct request from Microsoft founder and philanthropist Bill Gates himself, who has been supporting efforts to wipe out diseases such as polio and measles across the world, Jaklenec says. “If we don’t have good data, it’s really difficult to eradicate disease,” she says....."

https://www.scientificamerican.com/article/invisible-ink-could-reveal-whether-kids-have-been-vaccinated/