Image courtesy CDC/Smith Collection/Gado/Getty Images A US schoolboy receives his measles vaccination during field trials to determine the vaccine’s effectiveness in 1962 at Fernbank School in Atlanta, Georgia.

The measles are making a comeback in four European countries where the virus had been declared “eliminated.” Strains of the virus are now circulating yearround in the United Kingdom, Greece, Albania, and Czech Republic.

Measles elimination is generally a good sign that a country has a high vaccination rate, because it means that no single measles strain is able to stick around in-country for more than a year.

Measles is one of the most contagious viruses on the planet, and can spread in the air even after an infected person has left the room. 90% of unvaccinated people who are exposed will get it.

The US eliminated measles in 2000, but come October that may not be the case anymore.

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Measles, quite possibly the most contagious virus on the planet, is back with a vengeance across Europe and North America.

“We are backsliding, we are on the wrong track,” Dr. Kate O’Brien, Director of the World Health Organisation (WHO) Department of Immunization, told reporters on Wednesday.

The United Kingdom, Greece, Albania, and the Czech Republic had all previously declared that the measles was eliminated, but not anymore. Each of those countries has seen specific measles strains circulating for more than a year now, which means measles can no longer be declared “eliminated” within their borders.

Measles outbreaks mean not enough people are being vaccinated

The fact that four formerly measles-free countries are regressing is another indication that an increasing number of babies and kids are going without their vaccines. Public health experts say that in order to prevent the spread of measles, roughly 93-95% of a population must be vaccinated.

“When there’s no herd immunity, it just explodes,” Dr. Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases, recently told reporters at the National Press Foundation.

The measles virus can be deadly. It killed at least 37 people in Europe during the first half of this year, according to the WHO. Although vaccination coverage remains high across Europe, health experts are worried about growing “pockets” of vaccine hesitant parents across wealthy countries.

“The alarm bell that is ringing around the world is being able to achieve high national coverage is not enough,” O’Brien said. “It has to be achieved in every community, in every family, for every child.”

Measles may not be “eliminated” in the US for long

Since 2000, the measles has been declared eliminated in the US, but that could change come October. The measles has been circulating in both New York City and in communities in and around Rockland County, New York, since October 2018.

If those strains aren’t stamped out in the next month, the US will no longer be declared measles-free, Insider has learned from the CDC.

Read More: Photos reveal what it looks like to get the measles when there are no vaccines

The measles resurgence is happening across the globe. While the WHO cheered that both Switzerland and Austria eliminated the measles this year, and that measles cases are down slightly in the Americas, a staggering 364,808 measles cases have been tracked around the planet in 2019, the highest number recorded since 2006 – and we still have four months to go.

“This is almost three times as many cases reported as the same time last year,” O’Brien said.

At least 2,953 people have died of measles in the Democratic Republic of the Congo, more people than Ebola has killed there this year. Other countries experiencing worrying measles outbreaks include Madagascar, Ukraine, Nigeria, Philippines, and Thailand.

Ezra Acayan/Getty Images A Filipino child with the measles at a government-run hospital on May 4, 2019 in Manila, Philippines. The Department of Health in the Philippines declared an outbreak of measles early this year, with a total of 31,056 measles cases from January to April 2019, including 415 deaths.

There are lots of different reasons why these measles outbreaks are happening, but health experts say the backslide has a lot to do with vaccine hesitancy. O’Brien said many people in rich countries don’t “value” vaccines as much as they should.

“In some places we do see a complacency of parents, families, communities, and leaders to say these are diseases that we don’t see anymore, and this is not of high value,” she said. “It’s not worth spending time, energy, and potentially, you know, the discomfort of your child to get a vaccination.”

“We will continue to see an escalation of cases unless substantial and significant action is taken,” O’Brien said.

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