Minnesota reported 22 measles cases in 2022 — its third-highest total since 2000, when the disease was declared eradicated in the United States — but state health officials said the outbreak could have been worse.
Quick responses by doctors, public health officials and Minnesota parents prevented five measles clusters among children from exploding, despite measles being one of the fastest-spreading viruses on the planet.
"The timing and speed of the response is what was really critical," said Jayne Griffith, a senior infectious disease epidemiologist with the Minnesota Department of Health.
The state's measles count was the highest since 2017, when an outbreak of 75 infections was concentrated largely among unvaccinated Somali children at two child-care sites. Last year involved five distinct outbreaks spread over Hennepin, Ramsey, Dakota and Scott counties.
Fourteen of the cases involved people who had brought infections back from travels in Somalia, Kenya and Norway. Only eight involved domestic transmission, and all of those came from close relatives.
State health officials discussed the measles outbreak in an interview Friday, in part to show that effective public health responses can work but also to highlight the hazards when too many people go unvaccinated. The Centers for Disease Control and Prevention on Thursday reported that Minnesota's measles vaccination rate was 89% for kindergartners in the 2021-2022 school year, below the national rate of 93.5%.
Minnesota started to catch up in the most recent school year, but more children need to receive the measles vaccine, which has proven safe and long-lasting, said Jennifer Heath, a supervisor in the state Health Department's vaccine preventable disease section.
"The most dangerous thing about not having good MMR rates is when you have a pocket of kids or cluster of kids that aren't vaccinated," she said.
Minnesota's prior experience with measles resulted in a savvy response in 2022, because even unvaccinated people understood the risks and cooperated when public health officials asked them to quarantine, Griffith said.
The second cluster identified in August involved school-age children 5 to 13 years old — which itself was unusual because measles often is found in infants before their scheduled first MMR vaccine doses at 12 to 15 months of age.
People with measles are considered infectious four days before characteristic rashes appear on their bodies, so health officials had to identify a wide band of close contacts at schools and identify the unvaccinated, who needed to be quarantined.
Some measles patients had been in clinic and hospital waiting rooms while infectious, so health officials identified close contacts in those environments and whether there still was time for prophylactic treatment. Measles vaccine remains effective if given within three days of exposure and immunoglobulin therapies can be given within six days.
Parents deserved praise for alerting others to measles risks from their infected children, Heath said: "They understood ... the severity of the situation and they knew to contact anyone that their child may have been around."
Although 21 of the infections involved non-Hispanic black children, including children from Minnesota's Somali immigrant community, health officials said they didn't want to accentuate those demographics. The heavy focus on Somalis during the 2017 outbreak stigmatized the community and hurt efforts to improve vaccination rates in a hesitant population.
"When vaccine misinformation gets a foothold in any community, its dangerous," Heath said.
Some countries have emerged as measles hotspots during the COVID-19 pandemic because vaccination rates have lagged. However, Heath said an unvaccinated person now will face risks just traveling to Ohio — which has reported more than 80 measles cases in an ongoing outbreak.
Minnesota's 2022 outbreaks are considered over. More than two incubation periods have passed since the last measles case in Minnesota was detected, indicating no further transmission, Griffith said.
About a third of cases result in hospitalization. The disease can be fatal or cause complications such as pneumonia and an inflammation of the brain known as encephalitis.
Measles has one of the highest basic reproduction numbers; one person likely would spread the virus to 12 to 18 other unvaccinated people without any intervention. The comparable rate for influenza is only one to two. Minnesota gained a dramatic lesson about transmissibility in 1991, when measles spread from a Special Olympics athlete on the Metrodome turf to fans in the upper deck.
