The island nation of fewer than 200,000 has tallied 2,427 measles cases in the outbreak thus far, with more than 10% of those recently reported over a single 24-hour period, according to the ministry of health.
In an effort to stem the infectious disease's transmission, the government declared a state of emergency on Nov. 15 and initiated a mandatory vaccination program for priority groups, including children and women of childbearing age who aren't pregnant.
The best protection against measles is getting the measles, mumps and rubella (MMR) vaccine, according to the Centers for Disease Control and Prevention. It typically takes about 10 to 14 days for the vaccine to become effective.
Since Samoa's mass vaccination campaign started on Nov. 20, at least 24,000 people have been immunized against measles.
This has been an explosive year for measles, with cases jumping 300% worldwide during the first three months of the year, including major outbreaks in the Democratic Republic of Congo, Brazil, Ukraine, the Philippines, as well as in the United States, according to the World Health Organization.
More than 110,000 people died of measles in 2017, according to the WHO.
"Our measles campaign is ongoing," Leausa Take Naseri, Samoa's director general of health, said at a news conference Monday.
The country has dispatched teams to help district hospitals, he said, and was receiving assistance from Australia, New Zealand and French Polynesia, as well as guidance from the WHO.
"We still have a big problem at hand," Naseri added.
Low vaccination rates and a deadly medical mistake
The measles outbreak in Samoa didn't come out of nowhere.
Prior to the outbreak, Samoa had notoriously low vaccination rates, with data from the WHO and UNICEF estimating that the country's national immunization coverage fell from 74% to 34% between 2017 and 2018.
At that time, the country was embroiled in a medical scandal involving the deaths of two Samoan infants, who received improperly prepared MMR vaccines, which were administered by local nurses.
Following the July 2018 deaths, the government halted its MMR immunization program from July 2018 until April 2019 while it investigated, according to the WHO.
In early 2019, two nurses were sentenced to five years in jail for negligently preparing the vaccines by using a muscle relaxant instead of water to reconstitute them.
"Obviously an event like that causes a huge amount of fear and hesitancy around vaccination," said Nicola Hawley, an assistant professor of epidemiology at Yale School of Public Health whose research includes ongoing projects in Samoa. "That's something that Samoa has really been up against in the last 12 months."
In some ways, this is a straightforward story about Samoa's low vaccination rate, explained Julie Leask, a professor at the University of Sydney who researches vaccine hesitancy.
"If you don't keep vaccination rates high, measles will spread quickly and effectively," she said. "In other ways, it's a complex story and many questions need to be asked. How the nurses so easily missed the dilutent and what systemic issues contributed to this error in administration."
In the midst of a vaccination crisis, anti-vaxxers visit Samoa
In June, just months before the outbreak, two well-known and well-established anti-vaccine advocates, Robert Kennedy Jr. and Taylor Winterstein, the wife of an Australian rugby player, met in Samoa.
While it's not known what the two discussed, Winterstein, who posted an Instagram photo of herself with Kennedy at the time, has been spreading anti-vaccine conspiracy theories related to Samoa throughout the outbreak.
Helen Petousis-Harris, a vaccine expert at the University of Auckland, said that spreading misinformation online, in an environment in which people were reasonably fearful, was "altogether really unfortunate."
While the country's low vaccination rates ultimately primed it for a measles outbreak, anti-vaccine propaganda isn't helping matters, according to Petousis-Harris.
"It's a small place. Word spreads fast," Hawley said. "The government messaging is getting out pretty quickly. But that anti-vaccine conversation can spread equally quickly. Everybody talks."