Several countries that had previously been declared measles-free saw new cases - eroding progress against the disease which is highly preventable, but potentially deadly.
Brazil had the third most cases of measles in 2018 with 10,262.
"This is a wake-up call", UNICEF's Fore said. "We have a safe, effective and low-cost vaccine against a highly contagious disease - a vaccine that has saved nearly a million lives every year over the last two decades". Encephalitis-a risky condition that involves swelling around the brain-happens in about 1 in every 1,000 measles cases.
She added that a "lack of action today will have disastrous consequences for children tomorrow".
Although measles was officially eliminated in the U.S.in 2000, and the rate of measles vaccination coverage is fairly high nation-wide, "there are pockets of people who are vaccine hesitant who delay or even refuse to vaccinate themselves and their children", which can cause outbreaks, Messonnier said.
Although Clark County has the most cases, other confirmed measles cases have been identified in King County and the Portland area.
The virus can live for up to two hours in the air or on nearby surfaces. According to the Centers for Disease Control and Prevention (CDC), "Measles starts with fever, runny nose, cough, red eyes, and sore throat".
Right now, doctors are recommending a two-dose vaccine for everyone.
Before vaccination against measles became available in the U.S.in 1963, the disease killed 450 to 500 people annually nationwide.
Dr. Demetre Daskalakis says this is because "there are some folks who cite sort of religious reasons why they don't vaccinate".
Brazil, which had no reported cases in 2017, recorded 10,262 previous year.
It said the number of measles cases increased six-fold between 2017 and 2018 in the United States, reaching 791.
Measles is an extremely contagious and, in rare cases, deadly infection that was once thought to be almost eliminated from the United States due to widespread vaccination of children with the measles-mumps-rubella (MMR) vaccine.
"The overwhelming scientific evidence over many years and decades indicate that the vaccine, particularly the measles vaccine is very safe", Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Disease, told CBSN AM last month. The protestors argue, citing suspect science and anecdotal stories, that vaccines carry health risks to those who get them. The risk of measles and its complications is highest for unvaccinated young children, World Health Organization says.
The WHO last month listed "vaccine hesitancy" among the top 10 most pressing global health threats for 2019.
"I'm really concerned about the misinformation, but I also understand how complicated it is for parents", Messonnier said.
UNICEF's report comes as lawmakers debate anti-vaccination legislation that would allow parents to easily opt out of vaccinating their children, the Washington Post reported.