The United States recorded 695 cases of measles in 2019, the most of any year since the disease was declared eliminated in 2000, health authorities said Wednesday.
"The high number of cases in 2019 is primarily the result of a few large outbreaks -- one in Washington State and two large outbreaks in New York that started in late 2018," the Centres for Disease Control and Prevention said in a statement.
The resurgence of the once-eradicated, highly-contagious disease is linked to a growing anti-vaccine movement in richer nations -- which the World Health Organisation has identified as a major global health threat.
Outbreaks in the United States have mostly been confined to tight-knit communities where vaccination rates are lower than the national average of more than 90 percent.
People infected with the virus brought it to the United States from Israel and Ukraine and passed it on to members of their communities, many of whom had not been vaccinated.
New York and Washington State have been the main areas affected but cases have been found in 22 states.
"A significant factor contributing to the outbreaks in New York is misinformation in the communities about the safety of the measles/mumps/rubella vaccine," CDC said.
In a separate statement confirming the new record, Health and Human Services Secretary Alex Azar said "measles vaccines are among the most extensively studied medical products we have, and their safety has been firmly established over many years."
He added that next week, during National Infant ImmuniSation Week, his department will carry out "a comprehensive campaign to reinforce the message that vaccines are safe and effective."
In New York, an Orthodox Jewish community in Brooklyn has been hardest hit. They were infected by visitors from Israel, where an outbreak of the potentially life-threatening illness began a year ago.
STATE OF EMERGENCY
Earlier this month New York's mayor declared a public health emergency in parts of Brooklyn, ordering all residents to be vaccinated to fight the measles outbreak.
Washington state's Clark County has seen the outbreak concentrated among a Russian-speaking community. A child brought the virus back from Ukraine in December and it spread to 74 other people, mostly children, through schools, supermarkets and a bowling alley.
The state, in the country's northwest, declared in January a state of emergency over an outbreak of the airborne infection that causes fever, coughing and rashes that can be deadly in rare cases.
The so-called anti-vax, or anti-vaxxer phenomenon has adherents across Western nations but is particularly high profile in the US, where it has been fuelled by medically baseless claims spread on social media.
Tens of thousands of cases of measles have been reported in Africa and Europe. Ukraine alone has more than 30,000 cases and 11 deaths since January.
Worldwide, measles cases rose 300 percent through the first three months of 2019 compared with the same period last year, according to the United Nations.