In 2016, California's Senate Bill 277 (SB277) ended personal-belief exemptions from school immunization requirements. Medical exemptions remained — granted by individual physicians for reasons including family medical history, not by a single standard of medical contraindication — and some students without contraindications have received them. This outbreak in March 2018 shows the consequences.
How it spread
Measles transmission from community exposures to people who had not received MMR vaccine, by date of rash onset, California, March 2018. Patients A–E had measles genotype D8; the parents of patients F and G did not consent to testing. CDC.
| Patient | How infected | |
|---|---|---|
| A, 15 | unvaccinated boy, back from England and Wales, where measles was spreading; seen March 4 with fever, cough, coryza, conjunctivitis, Koplik spots and rash; confirmed by the Santa Clara County Public Health Department | the source |
| B, 16 | unvaccinated boy, reported March 23 — 19 days after A | at a scouting event with A, which A had not mentioned, so B was never contacted |
| C, 15 | unvaccinated classmate of A; fell ill March 24, in quarantine | school |
| D, 21 | man with 2 doses of MMR; reported April 2 in Washoe County, Nevada, after returning to college | at a different scouting event with B |
| E, 33 | unvaccinated man, reported April 3 in Alameda County | named his nephew as the source, but wouldn't give contact details |
| F, 7 | E's nephew, unvaccinated | at a tutoring center A attended; found only after health staff visited the home |
| G, 4 | F's unvaccinated brother | household |
Hundreds of contacts of the seven patients were traced across 10 counties in California and Nevada.
Protecting the vulnerable
- Patient A's brother, an organ transplant recipient with a weakened immune system, had been given intravenous immunoglobulin against measles before traveling abroad. Health officials advised more immunoglobulin and 7 more days of quarantine; the family did both.
- Patient C's unvaccinated 17-year-old sister was allowed by her parents to decide for herself, and chose MMR vaccine.
- Patient D, fully vaccinated, had only mild, modified measles, and none of his many contacts at a large university caught it.
The exemption
All six unvaccinated patients had parents who chose not to vaccinate them. Patients F and G had identical, broad medical exemptions from all vaccines, written by a physician several hundred miles from where they lived. Patients E and G were the first documented measles cases in California infected by a child with a medical exemption since SB277. Had the health department been told the truth about F's vaccination status, those two illnesses — and the cost of tracing their contacts — might have been avoided.
MMR vaccine is recommended for everyone born in the United States since 1957 who has no contraindication. Quick public health action and high population immunity likely prevented a larger outbreak.
Sources
Based on Han G, Batra N, Vallejo A, Schechter R, Zipprich J, Harriman K, "Notes from the Field: Measles Outbreak in an Era of Stricter Immunization Requirements — California, March 2018," MMWR Morbidity and Mortality Weekly Report, volume 68, Centers for Disease Control and Prevention; a work of the United States government in the public domain. The report notes that patient E could have been infected by either F or G during a visit to their home on March 17.
Licence: CC0 1.0 (public domain) · Adapted from www.cdc.gov
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