My 2 mins of googling came up with more like 3.6B$ on malaria, but even 2B$ is a shit-ton of money. I certainly haven't donated 2% of my net value to malaria (and it's only on the order of 1/10000 of his!).
Malaria rates are down around 30% since 2010, thanks in part to Gates. He's likely saved thousands to hundreds of thousands of lives.
Malaria is just one part of his philanthropy. I'd love to see the numbers for Jeff Bezos or Elon Musk. It would be great to all billionaires follow suit with this kind of "easy decision".