Numerous measles outbreaks across the United States have renewed a debate over whether parents should be required to vaccinate their children. Some parents express concern that vaccinations could be harmful to their children, but scientific consensus on the safety of the measles, mumps and rubella vaccine (MMR) remains strong and surveys have found that most Americans see childhood vaccinations as beneficial.

In recent weeks, lawmakers in several states that experienced outbreaks have proposed legislation to remove or restrict the types of exemptions parents can claim for their children based on religious or personal beliefs.

Here are some of the key findings from our research on attitudes about childhood vaccination:

1 Most Americans believe the health benefits of the MMR vaccine are high and the risks are low. In a 2016 survey, 73% of U.S. adults said the health benefits of the MMR vaccine are high, while 66% saw the risk of side effects as low. Overall, 88% said the benefits of the MMR vaccine outweigh the risks, while 10% said the risks outweigh the benefits.

2About eight-in-ten Americans favor school-based vaccine requirements. Some 82% of U.S. adults said MMR vaccination should be a requirement “in order to attend public schools because of the potential risk for others when children are not vaccinated.” Meanwhile, 17% of Americans believed that “parents should be able to decide not to vaccinate their children, even if that may create health risks for other children and adults.” Majorities of Americans across demographic and educational groups supported school requirements for the MMR vaccine, although older adults were more likely than their younger counterparts to say vaccinations should be required to attend school (90% of adults ages 65 and older vs. 77% of those 18 to 49).

3 A majority of U.S. adults trust medical scientists a lot for information about vaccines. Some 55% of Americans said in 2016 that they trust medical scientists a lot to give full and accurate information about the health risks and benefits of the childhood MMR vaccine. Another 35% said they have some trust in medical scientists, while just 9% said they trust them not too much or not at all. High degrees of trust in other groups were much lower, however. For example, no more than one-in-ten Americans placed a lot of trust in elected officials (6%) and news media (8%) to provide accurate information about the MMR vaccine.

4People with low knowledge about science are also less likely to see high preventive health benefits from vaccines. While 91% of those with high science knowledge said vaccines provided high preventive health benefits, only 55% of those with low science knowledge agreed. In addition, those with low science knowledge were more likely to consider the risk of side effects to be medium or high (47% vs. 19% of those with high science knowledge). Americans who did not correctly recognize the definition for “herd immunity” were less likely to rate the benefits of the MMR vaccine as high and were comparatively more likely to see the risk of side effects as at least medium. (Herd immunity refers to the health benefits that occur when most people in a population have been vaccinated.)

5State legislators are considering changes to vaccination laws. All 50 states and the District of Columbia require students to be vaccinated to attend school. However, every state and the District allow children to forego vaccinations for medical reasons. States also grant exemptions based on religious or philosophical beliefs. As of July 2016, 46 states allowed exemptions based on religious beliefs and 17 states allowed philosophical exemptions for those who object to vaccination on personal or moral grounds.

Legislators in at least 11 states have introduced bills to limit or eliminate nonmedical exemptions, according to the National Conference of State Legislatures. An Oregon bill aims to strike nonmedical exemptions altogether. If passed, Oregon would become the fourth state to prohibit nonmedical exemptions, joining California, Mississippi and West Virginia. On the other side of the issue, lawmakers in at least nine states have proposed legislation to broaden access to vaccine exemptions, based on analysis of bills proposed to state legislatures in 2019. In addition, there are proposals in at least 10 states that would require health care providers to give patients information about vaccines before administering them.

Note: This is an update of a post originally published July 17, 2015. The original version of this post was written by Monica Anderson, a senior researcher focusing on internet and technology at Pew Research Center.