The ongoing measles outbreak linked to Disneyland theme parks exemplifies the increasing prevalence of vaccine hesitancy in the United States and the impact it can have on public health.
“Although the index case has not yet been identified, the outbreak likely started sometime between Dec. 17 and 20, 2014. Rapid growth of cases across the United States indicates that a substantial percentage of the exposed population may be susceptible to infection due to lack of, or incomplete, vaccination,” study researcher Maimuna S. Majumder, MPH, of Massachusetts Institute of Technology, and colleagues wrote in JAMA Pediatrics.
Maimuna S. Majumder
To estimate vaccination rates among those affected by the ongoing outbreak, Majumder and colleagues utilized the incidence decay and exponential adjustment method along with cumulative incidence data from the California Department of Public Health. Analysis indicated that measles-mumps-rubella vaccination rates among the exposed population could be as low as 50% and no higher than 86%.
Because of the highly contagious nature of measles, vaccination rates of 96% to 99% are required to preserve herd immunity and protect from outbreaks, the researchers wrote.
Forgotten, but not gone
Though vaccine-hesitancy is one of the most significant factors contributing to this outbreak and certainly the most highlighted, there are numerous other reasons why the United States has experienced serious measles outbreaks in the past 5 years.
“One of the problems is that we did so well with measles vaccine in the 1980s and 1990s that by 2000, measles was declared as eliminated in the United States,” Samuel L. Katz, MD, of Duke University, told Infectious Diseases in Children. “Many young families — parents as well as young health care workers, physicians and nurses — have never seen measles, so they do not have as much concern about it or awareness of it as did their predecessors.”
Before the measles vaccine was approved in 1963, there were an estimated 3 million to 4 million cases of measles annually in the United States. Of those, approximately 48,000 patients were hospitalized, 4,000 had encephalitis and 500 died, according to Katz.
Samuel L. Katz
Measles was so prevalent that mothers would diagnose the disease at home.
“Only 500,000 measles cases were reported, but it was such a common disease that who really bothered to report it? You didn’t need a physician to diagnose — mothers knew what measles looked like,” Katz said during a presentation at the St. Jude/PIDS Pediatric Infectious Diseases Research Conference in February.
Same disease, new landscape
That picture is quite different from how phsycians experience measles today. The success of the measles vaccine, which led to the disease’s elimination, has somewhat removed measles from the map. Children receive the vaccine as infants and then before entering kindergarten, and often, that is the last we hear of measles — until now.
“Today, measles is a difficult disease to talk to people about,” Katz said during his presentation. “The vaccine hesitancy which is purveyed through parts of the United States is because not only are parents unfamiliar with measles, but many physicians, nurses and health care workers have little familiarity with measles.
“The idea that measles is something to be worried about really had no impact until the Disneyland outbreak began.”
As of March 6, there have been 173 cases of measles across 17 states and the District of Columbia, according to the CDC. Of these, 73% are related to the Disneyland outbreak. Katz urged health care workers to broach the topic of measles vaccination firmly but cautiously with parents.
“I think physicians have to be very careful to encourage parents to have their infants appropriately immunized against all vaccine-preventable diseases,” he said during an interview. “With measles, we have to be cognizant of the fact that children receive their first dose of measles vaccine as MMR at age 12 to 15 months and the second dose when they are preparing to enter school. It takes a lot of diplomacy, tact and time for physicians and nurses to work with parents who are uncertain or hesitant or even anti-vaccination.” – by Amanda Oldt
CDC. Measles cases and outbreaks. Available at: http://www.cdc.gov/measles/cases-outbreaks.html. Accessed March 13, 2015.
Katz SL. Measles, forgotten but not gone. Presented at: St. Jude/PIDS Pediatric Infectious Diseases Research Conference; Feb. 20-21, 2015; Memphis, Tennessee.
Majumder MS, et al. JAMA Pediatr. 2015;doi:10.1001/jamapediatrics.2015.0384.
Disclosure: The researchers report no relevant financial disclosures.