Racing to contain the measles outbreak that has killed 60 people amid low vaccination rates, the government of Samoa has turned to a twist on a disease-control tactic going back centuries.

Officials told the public Tuesday to hang red flags or cloth outside houses where people have not been vaccinated, to help teams embarking on a massive door-to-door campaign giving free booster shots.

The government plans to canvass the entire country of 200,000 over two days later this week while shutting down both the "public and private sectors" — the latest urgent measure in a health crisis that's hit the South Pacific nation's children hardest.

Vaccination for all Samoans ages 6 months to 60 will be free, the government said, but the top priority is children under age 4 because they are most at risk of deadly complications and also have the lowest vaccination rates.

Of the more than 4,000 cases reported, the government announced Tuesday, 171 were recorded in the past 24 hours, and 90 of those involved children 4 or younger. Most of the deaths to date are from that age group, too.

Prime Minister Tuilaepa Sailele Malielegaoi promised Wednesday to bring vaccination coverage up sharply, from about 55 percent to 90 percent, the BBC reported.

"Our children and people will never become immune to any future epidemic unless we have almost 100 percent vaccination coverage," he said on a hospital tour.

Samoa's government has taken all the right steps to combat an outbreak that's reportedly sickened more than 2 percent of the population, said Rene Najera, an epidemiologist at the Johns Hopkins Bloomberg School of Public Health and editor of the educational site History of Vaccines.

They've closed schools, sent out mobile clinics and sought to raise awareness with photos of leaders, including the prime minister, getting their shots.

But they're also battling public mistrust after a vaccine that was improperly mixed with a muscle relaxant led to the deaths of two infants, conviction of two nurses on manslaughter charges and a drop in immunizations last year.

Anti-vaccine groups targeted Samoa and Samoan communities in the United States and New Zealand after the scandal to spread falsehoods, Najera said.

And measles is extremely contagious, making an outbreak difficult to beat back. It can linger for about four hours in a room where a sick person exhaled, Najera added, leaving anyone who passes through during that time with a high chance of catching the disease.

According to Najera, it takes about 93 percent vaccine coverage to prevent a measles outbreak in a community. The government hopes red flags will expedite its huge door-to-door undertaking as it chases that goal.

"We need all the help we can get," Disaster Advisory Committee Chairman Ulu Bismarck Crawley said, according to the Samoa Observer.

Najera has never heard of flags being used to indicate places where people need vaccination. Samoa's tactic is an adaptation of the old practice of designating infected areas with such markers, part of a "quarantine" strategy that experts say had many flaws.

Historians say the practice popped up amid the Black Death that ravaged Europe in the Middle Ages, killing an estimated 50 million people. It made its way to America as places wary of smallpox marked taverns and brothels visited by infected sailors, Najera explained.

Fighting an outbreak of yellow fever in 1888, Florida officials flew yellow flags at afflicted houses, posting multiple guards to each one "night and day" and cordoning off "areas of infection" with rope.

An Indiana Board of Health document, also from the late 1800s, describes "flags of warning" posted outside buildings to broadcast the recent presence of scourges such as smallpox and cholera. The markers should stay up for at least two weeks, the health board advised, though it added one week was enough to prevent contagion for measles.

"Historically, quarantines have not really worked," Najera said, attributing the continued spread of diseases in part to the fact that many people don't realize they have illnesses such as measles and influenza until they've been contagious for some time.

Flag systems have also helped officials inspect incoming ships as they try to curb the spread of infection. In the 1600s, Venice required boats suspected of harboring plague to signal church-tower lookouts with a flag, according to the U.S. Centers for Disease Control and Prevention.

The captain would then have to prove the health of all crew and passengers as well as give documentation on any merchandise headed for the Italian commercial hub.

The approach persisted hundreds of years later across the Atlantic, as the U.S. government gained increasing authority to curb incoming disease in the 1900s. A public health vessel brought inspectors aboard ships flying a yellow flag, which didn't come down until the ship was cleared to dock, according to the CDC.

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