In 2019, more than 1,200 people — mostly unimmunized children — contracted measles in the United States. Some were hospitalized in an intensive care unit with measles pneumonia or measles encephalitis. The 2019 outbreak was larger than any measles outbreak in the past 20 years.

Child-to-child transmission of measles virus was eliminated in the United States in 2000. The reason that the disease is coming back is that a critical number of parents have chosen not to vaccinate their children. While education about measles vaccine and measles disease can influence some parents, others are steadfast in their desire to leave their children — and those with whom their children come into contact — at unnecessary risk. Is it a parent’s right to allow their children to catch and transmit potentially fatal infections? Some states have decided that the answer to that question was, no. One was California. In 2016, California, a state that had suffered a massive measles epidemic in 2014-2015, introduced a bill to eliminate its philosophical exemption to vaccination (SB277). Because California doesn’t have a religious exemption to vaccination, only medical exemptions remained. Three years have passed since that bill became law.

To determine the impact of SB277, Nyathi and coworkers examined immunization rates in California (Nyathi S, Karpel HC, Sainani KL, et al. The 2016 California policy to eliminate nonmedical exemptions and changes in vaccine coverage: An empirical policy analysis. PLoS Med. 2019 Dec 23;16(12):e1002994. They found that at the state level, immunization rates increased by 3.3%, nonmedical exemptions decreased by 2.4%, and medical exemptions increased by 0.4%. The increase in medical exemptions might have been caused by physicians willing to write a medical exemption where none existed.

The authors concluded that, “… government policies removing non-medical exemptions can be effective at increasing vaccination coverage.”

Materials in this section are updated as new information and vaccines become available. The Vaccine Education Center staff regularly reviews materials for accuracy.

You should not consider the information in this site to be specific, professional medical advice for your personal health or for your family's personal health. You should not use it to replace any relationship with a physician or other qualified healthcare professional. For medical concerns, including decisions about vaccinations, medications and other treatments, you should always consult your physician or, in serious cases, seek immediate assistance from emergency personnel.