A review of 18 measles studies and 32 pertussis studies published last week in the Journal of the American Medical Association (JAMA) found that parents who intentionally do not have their children vaccinated contribute to disease outbreaks, though other factors are likely at work, as well.
Measles and pertussis (whooping cough), both highly contagious, are on the rise in the United States. Measles was declared eradicated from the United States in 2000 but has recently resurged, with 667 cases in 2014 and 189 in 2015, according to the Centers for Disease Control and Prevention (CDC). Pertussis dropped to fewer than 2,000 US cases for several years in the 1970s and '80s before roaring back to more than 48,000 cases in 2012, a 60-year high, according to the CDC.
The JAMA meta-analysis, conducted by a team led by Emory University researchers, involved 1,416 measles cases and 10,609 pertussis cases across the 50 studies.
Exemptions from measles vaccination
The experts looked at measles outbreaks from 2000 until November 30, 2015, including an outbreak linked to Disneyland in 2014 and 2015 that involved 111 cases.
Of the 1,416 cases analyzed, 56.8% had no vaccination history, the authors found.They also noted that, of the 970 measles cases with detailed vaccination data, 574 patients (59.2%) were unvaccinated despite being vaccine eligible, and 405 of those (41.8% of the total) had nonmedical exemptions—for religious or philosophical reasons, as opposed to medical reasons.
Those rates compare with 14.1% of outbreak case-patients having received a vaccine, with the remaining cases being ambiguous.
One of the 18 studies that the researchers analyzed claimed that children who are not fully vaccinated are 35 times more likely to become infected with measles.