Measles is notorious for moving quickly through a non-immunized population, but a large outbreak in Minnesota presented another challenge. As public health officials and hospitals moved to rapidly immunize people at risk, the clinical picture was clouded by numerous vaccine-associated rash illnesses (VARI).
“It’s estimated that this reaction can occur in about 5% of non-immune MMR vaccine recipients, and it can be clinically indistinguishable from measles,” said Rajal Mody, MD, MPH, a CDC epidemiologist assigned to the Minnesota Department of Health in St. Paul.
Mody presented the results of the investigation recently in San Diego at the IDWeek conference.
“Even routine measles testing doesn’t really help because it is going to be positive for both true measles as well as VARI,” he said. “Although it is not considered contagious, and is not really that much of a medical risk factor — it’s not dangerous to people who have it — it does pose risks of unnecessary isolation of patients, unnecessary contact investigations, and post-exposure prophylaxis. All of this is really a waste of public health resources at a time when they are really limited due to a big outbreak investigation.”
During April through June 2017, Minnesota was hit with the largest measles outbreak in the state in 27 years. In another chapter to a familiar story, a disease once declared eradicated in the U.S. exploded in a population that did not vaccinate their children. Somali families living in Minnesota feared onset of autism with receipt of measles-mumps-rubella (MMR) vaccine, an association that has been thoroughly debunked time and again by the CDC and independent epidemiologists.
“Anti-vaccination advocates latched on to the Somali parents’ fears and passed on misinformation that MMR was the cause,” Mody said. “The outbreak disproportionately affected children of Somali descent.”
The index case in the outbreak was a one-year-old child of Somali descent with no history of travel or known exposures. The child went to two daycare centers attended by other Somali children, and these children went on to multiple other daycare centers.
“The index patient set off a chain reaction,” Mody said. “Transmission occurred in over five daycare centers, two schools, one hospital, and at least 16 households. We investigated over 8,400 exposed contacts. About 8% or 700 people were susceptible to measles and the public health department excluded more than 500 people from public settings, such as schools and non-emergency healthcare visits.”
The outbreak vaccine protocol was an accelerated two-dose MMR recommendation for children.
“They would have the first dose at 12 months and the second dose as early as 28 days following the first dose,” he said. “We initially gave this recommendation for the highest-risk children, those in Hennepin County and Somali children statewide.”
As vaccination and testing increased so did suspected VARI, which was defined as a rash occurring in a person within 21 days after receipt of MMR vaccine, and in whom a measles vaccine strain was detected in nasal or pharyngeal swabs or urine samples. More than 42,000 MMR doses were administered during the outbreak. Mody and fellow investigators ultimately identified 71 measles cases and 30 cases of VARI. The median age of VARI patients was 1.2 years, and for measles cases 2.8 years.
VARI diagnosis increased with rising MMR administration, with rash onset occurring a median of 11 days after immunization. The clinical presentations between VARI and measles can be hard to discern, but an epidemiological link to a known case is a strong indicator that it is a real measles infection.
“Presence or absence of measles exposures is an important distinguishing factor,” Mody said.
- Martin K, Mody R, Desilva M, et al. Sorting the Wheat from the Chaff: Vaccine-Associated Rash Illness Occurring amidst a Large Measles Outbreak — Minnesota, 2017. Abstract LB-8. IDWeek 2017. Oct. 4-8, 2017. San Diego.