California measles outbreak fueled by parents who failed to vaccinate children

The rapid spread of measles cases in the US after an infected person visited in Disneyland in December was largely fueled by parents who refused to properly vaccinate their children, a new study published this week has found.

Although the person who started the outbreak has not yet been identified, officials suspect it began with an infected person from abroad who visited the Disneyland theme park in southern California in mid- to late December. Since then, there have been 145 confirmed measles cases in seven states and three countries linked to the Disneyland outbreak, according to the Centers for Disease Control and Prevention (CDC).

“This preliminary analysis indicates that substandard vaccination compliance is likely to blame for the 2015 measles outbreak,” the authors wrote in a research letter published this week in the JAMA Pediatrics journal.

Using data from the Disneyland outbreak, the team of experts found that the measles cases occurred in areas where the vaccination rate was far lower than the minimum recommended threshold needed to protect everyone in the community – typically a rate above 95%.

Vaccination rates among the people exposed to measles during the outbreak may have been as low as 50% and probably no higher than 86%, according to the study.

“Even the highest estimated vaccination rates from our model fall well below this threshold,” the researchers wrote.

Though the national vaccination rate for the measles, mumps and rubella (MMR) vaccine is around 92%, there are communities with pockets of under-vaccinated or unvaccinated children, where an outbreak is much more likely to take hold.

Experts say the high vaccination threshold for herd immunity – the idea that a highly immunized community makes it difficult for a disease to spread easily – is necessary because measles is one of the most contagious diseases.


Officials are urging people to vaccinate: “The measles vaccine is safe and highly effective, and it is the best way to protect you and your family.” In January, Anne Schuchat, director of the CDC’s National Center for Immunization and Respiratory Diseases called the outbreak “a wake-up call to make sure we keep measles from regaining a foothold in our country”.

Health officials declared measles eliminated in the US in 2000 after decades of intensive childhood vaccine efforts led to widespread vaccination.

But a resurgence of the disease in recent years – linked to the rise of a movement among largely wealthy and well-educated parents who resist calls to inoculate children, often claiming erroneously that vaccinations are linked to mental impairment – has public health officials concerned. Last year, the nation saw its highest number of measles cases in two decades.

Measles transmits through coughing, sneezing and contact with a sick person or with contaminated surfaces. It is contagious four days before a rash appears and four days afterward. Measles and its complications, including encephalitis and blindness, were linked to 145,700 deaths worldwide in 2013.