Gates doesn't need to know much about either. Gates is one of those 'different level' businessmen like Rockefeller was. Rockefeller didn't know crap about medicine or the medical industry, but he took control of it fairly quickly. Hell, at one point, he tried to go after the steel industry and take on Carnegie.Why does Gates believe he understand anything about vaccines and immunology?
These other level businessmen like Gates and Rockefeller know business, money, and power. At some point in their career, money becomes worthless to them, so they focus their attention on power. Back in the mid-90s when the internet was good, there were some amazing theories surrounding Gates and the lawsuit leveled against him and Microsoft by the federal govt. Apparently... Gates knew where the power lies, and he started to dabble in banking which is controlled by a tight knit group of families, and they sent their attack dog after Gates to get him under control.
He got the hint and moved on to owning a good portion of Monsanto. Then pharma, then farming. Next would be water but like Banking, that too is controlled by a tight group of people who also happen to own some of the world's largest PMC.
Maybe that is something Gates can get into. He has the money and power to start a high-tech PMC and compete with the big boys for war contracts.