In measles outbreaks, those who passed on vaccinations are most often the patients

Los Angeles Times

A comprehensive new study of measles and pertussis outbreaks in the United States suggests that adults' reluctance or refusal to vaccinate themselves and their children have played a key role in the resurgence of diseases that had been completely or largely eradicated in this country.

In an analysis published Tuesday in the Journal of the American Medical Assn., epidemiologists scoured published and public-health reports of measles and pertussis outbreaks to glean what role vaccination refusal and hesitance played, and how significant the contribution of waning immunity was among the vaccinated.

In measles outbreaks, the researchers found the role of the unvaccinated to be powerful. In 1,416 measles cases occurring in the United States since the disease ceased to circulate in the United States in 2000, 57% were in people who had no history being vaccinated. Of the 574 cases of measles seen in unvaccinated individuals, 405 (almost 71%) were unvaccinated due to nonmedical exemptions.

Using the reports to draw a "cumulative epidemic curve" -- the trajectory of the infection's spread -- the researchers found that unvaccinated individuals tended to be among the first, or within the first few groups of people to contract and pass along measles. That suggests that unvaccinated people ignited many of the outbreaks, and were a key accelerant in their spread as well.

In children under 5 and adults over 20 who contract measles, complications are more common and can be serious. Inner ear infections, which can cause hearing loss, are not unusual. As many as 5% of children who get measles will develop pneumonia and one in 1,000 will develop swelling in the brain, which can cause seizures and lead to deafness or intellectual disability. Death is a rare complication, but occurs in one to two children per 1,000 infected.

The new research found a slightly different picture looking at pertussis outbreaks. Of the more than 10,000 cases that occur annually, outbreak frequently occurred among the vaccinated -- evidence that vaccination with the DTaP (the combination vaccine against diphtheria, tetanus and pertussis) is not conferring lasting immunity in all who get it.

Researchers reviewed 32 reports of pertussis outbreaks in which the vaccination status of the 10,069 patients was known. Unvaccinated and undervaccinated individuals accounted for between 24% and 45% of the infected in five of the largest statewide epidemics included in the analysis. [...]