Outbreak Tracker

Outbreak Tracker

Issue: April 2018
April 16, 2018
6 min read

US measles outbreaks catalyzed by vaccine hesitancy

Issue: April 2018
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Just 14 years after the elimination of endemic measles was documented within the United States, a record 667 cases of the disease were reported in 2014 in 27 states, a dramatic spike compared with the 55 cases reported in 2012.

Potential exposure to measles has more recently been reported at U.S. airports in 2017 and 2018, including a potential exposure occurring in March in three airports.

Pia Pannaraj

Although the virus is easily prevented through vaccination with two doses of the measles, mumps and rubella (MMR) vaccine, immunization hesitancy has interfered with maintaining a high coverage rate. An unsupported link between autism and MMR vaccination persists, and several outbreaks and exposures have occurred in pockets of the country with lowered vaccination rates.

Although measles is no longer endemic to the U.S., it is one of the leading contributors to child mortality around the globe, according to WHO. The CDC notes that this disease is common in other areas around the world, including countries in Europe, Asia, the Pacific and Africa. Vaccination has lowered mortality due to measles by 84% from 2000 to 2016 saving approximately 20.4 million lives.

To better understand the barriers to measles vaccination and the elimination of the illness and how pediatricians can stay at the forefront of prevention, Infectious Diseases in Children spoke with physicians and epidemiologists about recent events and how they can stay at the forefront of prevention.

Recent outbreaks and exposures

WHO reports that before the measles vaccine was introduced in 1963, major outbreaks were a common global occurrence, with two to three outbreaks occurring annually. These outbreaks led to approximately 2.6 million deaths each year.

“Since we have had access to the vaccine, we see much less measles,” Pia Pannaraj, MD, MPH, attending physician in the division of infectious diseases at Children’s Hospital Los Angeles and associate professor of clinical pediatrics and molecular microbiology and immunology at the Keck School of Medicine, University of Southern California, said. “We saw the numbers decrease to almost zero, but then in the last decade, we have started to see an increase again. A lot of that has to do with people not wanting to receive the vaccine.”

This increase has been evident on a global scale, with European Centre for Disease Prevention and Control reporting 14,451 measles cases in 30 countries in 2017, a number that more than triples the reported cases in 2016.

Notable outbreaks also have occurred in the U.S. in the past few years. One of the more pronounced outbreaks took place in two Disney theme parks in late 2014 and early 2015. According to the CDC, 125 cases were connected to this outbreak between Dec. 28, 2014, and Feb. 8, 2015. Of those who were residents of California at the time of infection (n = 110), 45% were completely unvaccinated, and 43% had no record of immunization or their status was unknown.


Areas such as amusement parks provide a favorable environment for the spread of disease because of the highly heterogenous populations from around the globe that mix in such settings, Gerardo Chowell, PhD, professor of epidemiology and biostatistics at the Georgia State University School of Public Health, told Infectious Diseases in Children. He noted that these individuals were especially susceptible to measles because “this is a highly transmissible pathogen; any opportunity that pathogen has to infect, it will take.”

“For other infectious diseases, someone could get exposed to the pathogen and not catch it and remain susceptible, but for measles the high probability of transmission per contact together with well-mixed places makes this a highly transmissible agent in susceptible communities,” he said. “It is key for populations to achieve a critical vaccination coverage to prevent outbreaks, which is generally above 95% of the population for measles.”

Gerardo Chowell

Pockets of unvaccinated communities can also increase the likelihood of measles transmission and increase susceptibility. One such example has been observed in an outbreak within a Somali-American community in Minnesota. This outbreak was spurred by decreasing rates of vaccination, which were mostly attributable to a perception of increased risk of autism in this community and a belief in the connection between autism and MMR immunization.

The outbreak in April and May 2017 led to 65 confirmed measles cases and an estimated 8,250 potential exposures throughout the state, according to an MMWR issued by the CDC.

Additional exposures have affected passengers in U.S. airports throughout 2017 and 2018, with the most recent potential exposures occurring in New Jersey, Michigan and Tennessee. State health officials have reported that one passenger arrived at Newark Liberty International Airport and one arrived at Detroit Metropolitan Airport in March with active cases. According to state officials, the passenger who landed in Newark later boarded a flight to Memphis, Tennessee.

“If you are out in a crowded area and you are exposed to somebody who is in the early stages of infection, there is no way to know because they will not yet be ill,” Pannaraj said. “However, they can still spread the virus. Those around them who are not vaccinated, are susceptible and at very high risk of getting the disease.”

How pediatricians can help

A practice alert published in The Journal of Family Practice suggests that those at greatest risk of infection are those who are unvaccinated. Most cases, according to the alert, were transmitted through contact with individuals who were infected in areas outside the U.S. Further spread of the disease is most likely to occur when an infected person comes into contact with a community with low vaccination rates.


Immunization against measles should begin in infancy, with the CDC recommending all children between the ages of 12 and 15 months receive their first dose of MMR. A second dose should be administered between the ages of 4 and 6 years, or a minimum of 28 days after the first dose of MMR.

Measles is normally considered a childhood disease, and young children who are unvaccinated are at the highest risk of infection and its associated complications, according to WHO. Although general symptoms of measles include a fever (temperature of up to 105°F), malaise, cough, coryza, conjunctivitis and a maculopapular rash, complications such as otitis media, bronchopneumonia, encephalitis and diarrhea can occur in some patients.

“I think people really are not aware of the potential complications of measles: pneumonia, its effect on the brain or that it can lead to death,” Pannaraj said. “All of those complications are much more common than any potential complication of the vaccine itself. I think we need to do a better job of making people aware of that and help people feel safe about getting the vaccine.”

In the practice alert, Doug Campos-Outcalt, MD, MPA, medical director at Mercy Care Plan, stresses that further transmission and outbreaks are preventable through measures that can be accomplished within the primary care setting or pediatrician’s office. These steps include fully immunizing all staff members, using the recommended schedules to vaccinate patients, using and upholding infection control strategies and appropriately diagnosing and treating suspected cases of measles.

“Pediatricians can play an important role in enhancing vaccination rates in their communities,” Chowell said. “They can remind patients at every visit about the importance of following vaccine schedules and particularly if they have identified clusters of families that systematically postpone recommended vaccinations. I think it is important for the pediatricians to consistently provide objective information to families including simple explanations of how vaccines have been instrumental in eradicating or controlling past scourges.”

“Perhaps physicians and those in public health have not yet done a good enough job to overcome some of the fears [related to vaccines and autism], but I think that parents also do not see measles anymore,” Pannaraj said about the role of medical professionals in the prevention of measles. “They do not realize how devastating the disease can be. Because of that, they are more fearful of the vaccine than they are the disease, and it really should be the other way around.” — by Katherine Bortz

Disclosures: Pannaraj reports receiving funding from AstraZeneca for an RSV study. Infectious Diseases in Children was unable to determine relevant financial disclosures for Chowell at time of publication.