Measles Outbreak Under Stricter Immunization Requirements

On March 1, 2019, the CDC published a report that described a measles outbreak in California and Nevada after California implemented stricter immunization requirements. Since California Senate Bill 277 (SB277) went into effect in 2016, children entering school in California may no longer receive exemptions from immunization requirements based on parental personal beliefs. However, medical exemptions for reasons determined by individual physicians, including family medical history, rather than a uniform standard (i.e., a medical contraindication to vaccination), remain permitted. Interviews with local health authorities suggested that some students without contraindications to vaccination have received medical exemptions. Two patients in this outbreak represented the first documented cases of measles in California infected by a child with a medical exemption, but no medical contraindication to vaccination, since SB277 became law.


An unvaccinated adolescent patient (patient A, aged 15 years) who had recently returned from England and Wales, where measles outbreaks were occurring, was evaluated by a physician for fever, cough, inflammation of the mucous membrane in the nose, conjunctivitis, Koplik spots (small, white spots on the inside of the cheeks), and rash. Measles virus nucleic acid was detected in an oropharyngeal swab and in urine tested at the county public health department.


Nineteen days later, measles was reported in an unvaccinated adolescent boy (patient B, aged 16 years) who had been at an event with patient A. Patient B was not contacted during the initial public health investigation because patient A had not reported attending this event. The following day, an unvaccinated classmate of patient A’s (patient C, aged 15 years) developed measles while in quarantine. Nine days later, a college student (patient D, aged 21 years) who had received two doses of measles, mumps, and rubella (MMR) vaccine and who had attended an event with patient B before returning to college out of state was reported as a measles patient to the health department in that state.


The following day, a second county health department received a report of measles in an unvaccinated patient (patient E, aged 33 years). Patient E identified a nephew (patient F, aged seven years) as the source of the illness, but declined to provide contact information. The first county public health department eventually confirmed the nephew’s presence at a tutoring center attended by patient A. The nephew’s mother was interviewed at their home. She acknowledged that her son was not vaccinated and revealed that both he and his unvaccinated brother (patient G, aged four years) had experienced recent illnesses consistent with measles.


Hundreds of contacts of these seven patients were traced across 10 counties in two states.


Although patient A’s parents had chosen not to vaccinate him, his immunocompromised brother, an organ transplant recipient, had received intravenous immunoglobulin to protect him against measles before traveling overseas. When patient A’s illness was reported, the county public health department recommended that his brother receive additional intravenous immunoglobulin and be quarantined seven additional days. The family followed both recommendations.


Patient C’s unvaccinated sister, aged 17 years, received parental permission to choose to receive MMR vaccine when her brother was quarantined. She opted to receive the vaccine.


Patient D, who had received two doses of MMR vaccine, exhibited mild symptoms consistent with modified measles. None of patient D’s many contacts at a large university developed measles.


MMR vaccine is recommended for all persons born in the United States since 1957 who do not have a contraindication for the vaccine. In this outbreak, the six unvaccinated patients with measles all had parents who had chosen not to vaccinate them during childhood. Patients F and G received identical broad medical exemptions to all vaccines from a physician located several hundred miles away from the patients’ residence. Patients E and G represent the first documented cases of measles in California infected by a child with a medical exemption since SB277 became law. Had the county public health department received accurate information about patient F’s immunization status, these two illnesses might have been prevented, and the expenditure of resources to investigate their contacts might have been avoided. Prompt public health action and continued maintenance of a high level of population immunity to measles likely averted a larger outbreak.


See the CDC Report


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