Education and the incentives of the market have encouraged lots of Americans to get themselves and their children vaccinated. Surely those avenues of persuasion have not been exhausted and should be used more. Perhaps schools and daycare centers could attract clients by advertising that they protect their charges by refusing to admit unvaccinated students. Or social pressure might be exercised by parents who insist on assurances from other parents that their children are vaccinated before agreeing to play dates. But it would be naïve not to note, writes Ron Bailey, that state requirements that public school children be vaccinated against many highly contagious diseases have more than merely nudged most parents into getting their children vaccinated.