Secret Agent by Michelle Larkin

Rogue agent Zoey Blackwood is having the time of her life traveling the world and evading the CIA's capture. Her wisecracking humor keeps things light, but her mission is no joke: save millions of innocent lives that the US considers expendable in the wake of a deadly virus. Giving away the vaccine's top-secret formula when the government plans to sell it lands her squarely on the CIA's most-wanted list.