A measles vaccine is seen at Venice Family Clinic in Los Angeles, California February 5, 2015. Lawmakers in several U.S. states are backing proposals to make it harder for parents to opt out of school vaccinations based on personal beliefs, as health officials fight a growing measles outbreak that has sickened more than 100 people in more than a dozen states. REUTERS/Lucy Nicholson (UNITED STATES - Tags: HEALTH POLITICS)