The measure, which defines a public place as anywhere "more than 10 persons are intended to congregate" — including public transport — was announced by officials in Rockland County, 25 miles (40 kilometers) north of New York City. Due to come into effect at midnight on Wednesday and last for 30 days, it appears to be the most radical step by US officials following outbreaks in several regions blamed on the anti-vaccination movement.

"We must do everything in our power to end this outbreak and protect the health of those who cannot be vaccinated for medical reasons and that of children too young to be vaccinated," said county executive Ed Day. He also criticized the "resistance" to health inspectors by some locals.

Rockland County, with a population of over 300,000, has registered 153 cases of measles, which had been declared officially eliminated in 2000. Despite major vaccination campaigns since the outbreak began in October, around 27 percent of minors aged one to 18 remain unvaccinated, Day said.

The worst affected neighborhoods are those with a high ultra-Orthodox Jewish population, where many oppose vaccines on religious grounds. Vaccinations are in theory required to go to school in the United States, but 47 of the 50 states — including New York — allow exemptions, notably for religious reasons.

Worldwide increase in measles cases

At the beginning of March, the UN Children's Fund UNICEF sounded the alarm because of the rapidly increasing number of measles cases in some regions of the world.

Worldwide, 98 countries recorded more cases in 2018 than in the previous year. Reports also came from countries that had previously been measles-free, including Brazil, where more than 10,000 people were infected with measles last year. In the Philippines, around 13,000 people have contracted measles and more than 76,000 have in Madagascar since last September. The situation is also particularly dramatic in Ukraine, where 24,000 people have been infected with the dangerous virus in the first weeks of this year alone.

Will vaccination become compulsory… in Germany?

According to the Robert Koch Institute (RKI), the number of reported cases in Germany fell from 929 in 2017 to 543 last year. Nevertheless, Germany is still debating controversially requiring measles vaccinations, originally demanded in March by the SPD health expert Karl Lauterbach. Most recently, Health Minister Jens Spahn (CDU) advocated for compulsory measles vaccinations for school-aged children.

But even their own parties had reservations about the proposals. Karin Maag (CDU), spokeswoman for health policy for the CDU/CSU parliamentary group in the Bundestag, rejected compulsory vaccination, partly because there is a lack of knowledge about the advantages of compulsory vaccinations as introduced in Italy and France.

The Robert Koch Institute has also been cautious. In Germany, for example, there was no noticeable increase in infections. Nevertheless, the vaccination rate could always be improved, especially among young adults.

Until the beginning of the 1990s, each person only received one vaccination against measles. It was difficult adopt the practice of getting a second vaccination, especially for those vaccinated prior to the 1990s. In contrast, 97% of school children in Germany have the first measles vaccination and 93% have the second vaccination. The second measles vaccination, which should be carried out by the end of the second year of life, is often carried out later. According to the RKI, only 74% of two-year-olds in Germany have full protection.

How do measles pathogens spread?

The first telltale sign someone has measles is a widespread itchy red rash. The spots are initially visible behind the ears, or on the neck or head. Three days before visible signs appear, the virus has peaked in the body. The infected person is contagious, usually without even knowing it. For a reliable diagnosis, patients suspected of having the virus need to have the antibodies in their blood tested.

The measles virus is transmitted directly through the air in the form of very fine droplets of saliva or mucus — usually from coughing or sneezing. But they can also be passed on simply when speaking to someone in close proximity.

Measles is highly contagious. Each contagious person infects around 15 healthy people. Humans are the only natural hosts of the measles virus. 

Read more: French boy suspected of reintroducing measles to Costa Rica

Often unpredictable

About 14 days after the initial infection, patients get a fever and start coughing. At that point, the red rash starts to itch.

To alleviate these symptoms, doctors usually administer medication. Patients may also get a middle ear infection, pneumonia or have severe diarrhea. In the worst case, diarrhea can lead to dehydration and ultimately death. There is no specialized treatment for measles. The body has to fight the infection itself.

Measles can cause meningitis, which can lead to severe brain damage and mental disability. According to Germany's main public health body, the Robert Koch Institute, measles encephalitis occurs in one in every 1,000 infections. One in five of these cases is fatal. Such complications do not necessarily occur during the original bout of the disease; they can occur years later. 

Read more: Top ten most dangerous viruses in the world

Vaccination is the best protection

Many parents refuse to vaccinate their children because they fear serious side effects. Some assume it is better for their children to be infected with the virus so their bodies can build up anti-bodies. For a while, measles parties were popular.

Parents would send healthy children to play with other children who had the virus in the hope they too might become infected. Parents who did this were often convinced that exposure to the virus strengthened their child's defenses if and when they got measles. 

Read more: Death toll from measles climbs in Philippines

Experts, however, are convinced this is not the case. False claims and beliefs contribute to vaccination fatigue. The myth that there is a connection between the measles vaccination and autism is just that — a myth — and one doctors have debunked many times over.

The measles vaccine includes two shots of attenuated measles viruses. The Permanent Vaccination Commission (STIKO) of the Robert Koch Institute recommends measles vaccinations in combination with inoculations for mumps and rubella. The vaccinations should take place just after a child turns one. Only then can parents ensure their child is protected from the dangerous virus.

Vaccination target missed

The WHO was committed to eradicating measles worldwide by 2020. The Czech Republic, Estonia, Finland, Portugal, Slovakia and Slovenia are the only countries to have achieved this goal so far.

Read more: WHO: Measles infections surge in Europe in 2018