The two highest level questions concerning vaccines are: (1) are they safe, and (2) are they effective. Public Health policy concerning vaccines has always been controversial. The question of whether vaccines should be mandatory, or simply recommended, has long presented a conflict between personal freedoms and public welfare.
The start of the most recent vaccine resistance movement is commonly attributed (with some rigorous support) to a now-retracted 1998 Lancet article that claimed there is a causal link between measles-mumps-rubella (MMR) vaccines and autism.
In response to the growing questions about the safety and efficacy of vaccines, then-president Barack Obama charged the National Academy of Sciences (a body of the nation’s leading scientists whose purpose is to advise presidents on matters of public interest in science) with the task of summarizing what is and is not known about vaccines that are recommended by the government. In 2012, they submitted a 900+ page report.
National Academies of Sciences, Engineering, and Medicine. 2012. Adverse Effects of Vaccines: Evidence and Causality. Washington, DC: The National Academies Press. https://doi.org/10.17226/13164.
On the most controversial issue concerning whether there is a link between the measles-mumps-rubella (MMR) vaccine and autism, the NAS found that “The committee has a high degree of confidence in the epidemiologic evidence based on four studies with validity and precision to assess an association between MMR vaccine and autism; these studies consistently report a null association.” They conclude
Conclusion 4.8: The evidence favors rejection of a causal relationship between MMR vaccine and autism. (NAS report, page 153)