From Jan 1 to Oct 1 of this year, the United States tracked 22 measles outbreaks and 1,249 cases, according to a new overview published today by the Centers for Disease Control and Prevention (CDC) in Morbidity and Mortality Weekly Report (MMWR).
The large number of cases nearly caused the country to lose its measles elimination status, obtained in 2000, the CDC said, and close-knit communities that eschewed the vaccine played a major role.
Fully 93% of measles cases were associated with an outbreak—defined as three or more related cases. The overview offers the most comprehensive picture of these outbreaks, and the forces that made 2019 the worst measles year the US has seen since 1992.
Three fourths of cases in Orthodox Jewish areas
"Eight outbreaks that occurred in underimmunized, close-knit communities accounted for 85% of all cases," the CDC said. And 75% of all cases in 2019 were part of outbreaks among Orthodox Jewish populations in New York State and City.
Under-vaccinated and unvaccinated people were the most likely to contract the virus; 89% of patients were not vaccinated with measles, mumps, and rubella (MMR) vaccine, and 11% received only one dose of the two-dose regimen. No deaths have been attributed to measles this year, but 119 case-patients (10%) required hospitalization. Twenty percent of the hospitalizations occurring in infants under the age of 1.
The median patient age was 6 years, with 13% of cases occurring in infants under 1 year, 31% of cases in children ages 1 to 4, 27% of cases in children ages 5 to 17, and 29% in adults.
Eighty-one cases were internationally imported measles cases, linked to ongoing outbreaks in Israel, Ukraine, and the Philippines. Of the 81 international cases, 52 were in US residents who contracted the virus during their time abroad.
New York outbreaks tied to foreign travel
While most outbreaks in 2019 were small and short-lived, the two New York–based outbreaks were persistent and lasted more than 1 year, the CDC said.
Both New York–based outbreaks had links to international travel. A Brooklyn outbreak that began in September 2018 started with a returning US traveler, and an outbreak in Rockland County began with an internationally imported cases in a foreign visitor on Oct 1, 2018.
The CDC said these two outbreaks were sustained "because of a combination of three important risk factors for measles transmission: 1) pockets of low vaccination coverage and variable vaccine acceptance; 2) relatively high population density and closed social nature of the affected community; and 3) repeated importations of measles cases among unvaccinated persons traveling internationally and returning to or visiting the affected communities."
Last NY outbreak called over
Yesterday New York State Health Commissioner Howard Zucker, MD, JD, announced that 42 days—two measles incubation periods—had passed in Sullivan and Orange counties without any new cases of measles.
"Reaching this milestone, as Rockland County did last week, means there are no longer any active cases in New York State associated with the initial measles outbreak from October 2018," Zucker said. "The threat, however, for vaccine-preventable diseases remains, and the Department is not letting down its guard."
To combat measles and end the outbreaks, New York state took several steps, including administering 75,000 doses of MMR in affected communities, and eliminating non-medical vaccine exemptions in public schools.
Oct 4 MMWR study
Oct 3 New York Health Commissioner statement