Game Settings->Science->Technology Cost Multiplier Percentage
Set this to 225.
So how does this prevent smallpox?
In order to get any decent number of bulbs per turn the player must have cities large enough to overcome the Tech cost multiplier percentage setting, this also dramatically improves the effectiveness of the library city improvement as opposed to small size 2-3 cities. In a chain reaction that dooms smallpox this causes yet another problem: happiness. Unless you want to swamp your shield production building military units you need to build a temple/courthouse at a minimum or better a Colosseum for larger cities. I have tried this setting with almost magical results: I continuously destroy smallpox players by the middle of the game. Early on until about 500 BC smallpox still seams to have an advantage, but then as we march towards gunpowder things change rapidly. As my libraries are built I start to take the tech lead, I see the AI players are all desperately trying to build the great library wonder to catch up to me. I usually get to gunpowder centuries ahead of them. By 1200-1400 AD the game is consistently a cake walk with me building all the wonders getting to things such as Navigation and reaching new continents and opening up trade routes. With the smallpox players are battling each other with bows and arrows land I show up with cannons and musketeers to demolish them all!
One setting changes the game completely!