The WHO on Thursday declared the China coronavirus outbreak an international public health emergency, marking an escalation in the global response to an outbreak that has sickened more than 8,100 people and killed over 170 in that country, and led to growing spread of the virus through person-to-person transmission in the United States, Germany, Japan and Vietnam.

The designation gives the global health agency the ability to ramp up the responses of governments and organizations around the world as they try to control the outbreak.

In making the announcement in Geneva, WHO chief Tedros Adhanom Ghebreyesus said the decision was made to prevent the further spread of the virus to countries with weak health systems that are “ill-prepared to deal with it.”

“This decision is not a vote of no confidence in China,” he said, emphasizing that the WHO “continues to have confidence in China’s capacity to control the outbreak.”

He praised China for the speed with which it identified the virus, sequenced its genome and shared it with the world, actions he called “impressive and beyond words.” There have been no deaths outside China, he said.

Although the number of cases in other countries is relatively small, he said, the world must “act together to limit further spread.”

The WHO is urging countries to avoid measures that would limit trade and travel to China, he said.

The global health agency is also calling for the world community to support countries with weak health systems, accelerate the development of vaccines, combat the spread of rumors and misinformation, ramp up preparedness and health-care resources to prevent further spread, and share data, knowledge and expertise with the WHO and the rest of the world.

This is the sixth outbreak that the WHO has voted to assign the designation of public health emergency, defined by the group as “an extraordinary event which is determined to constitute a public health risk to other States through the international spread of disease and to potentially require a coordinated international response.”

The five other cases have been:

– The 2009 swine flu epidemic that spread throughout the United States and Mexico.

– The 2014 polio infection, spurred by an “international spread of wild poliovirus” that hit countries including conflict-ridden Pakistan, Cameroon and Syria.

– The 2014 Ebola epidemic in West Africa, which the WHO said “was the largest and most complex Ebola outbreak since the virus was first discovered in 1976.”

– The 2016 Zika virus, which was spread by mosquitoes throughout the Americas and Africa and was particularly dangerous for pregnant women.

– The 2018 Ebola epidemic in North Kivu and Ituri provinces, which was the world’s second-largest Ebola outbreak. The WHO controversially waited until 2019 to declare it a public health emergency.

Experts say a vaccine for the virus is still a long way off. Schools in Beijing have closed indefinitely, and foreigners who have been evacuated from Wuhan, China, the city at the epicenter of the outbreak, are starting to arrive in their home countries or at temporary screening sites.

Chinese officials added more than 1,500 new cases of the coronavirus as countries stepped up their efforts to evacuate their citizens trapped in Wuhan.

About 50 million people in Hubei province have been restricted to their region as authorities try to stem the spread of the virus. Japan has sent a second flight to Wuhan, and a third is planned.

With experts saying a vaccine is not imminent, more international cases of the illness appeared Thursday. Australia, Vietnam and South Korea all announced new coronavirus infections, while India and the Philippines had their first ones.

Earlier Thursday, the United States confirmed a sixth U.S. case of the coronavirus, marking the first time the virus has spread from person to person in the United States.

The sixth U.S. patient is a Chicago resident who was infected after being in close contact with his wife, who had traveled to Wuhan. The Chicago woman was the second confirmed case in the United States. She is doing well, and he is in stable condition; both will remain in a hospital to keep them isolated.

The number of countries with human to human transmission of coronavirus now numbers five: The United States, Germany, Japan, Vietnam and China, which includes the self-governing island of Taiwan.

Illinois has 21 people it is monitoring for possible infection.

The U.S. government is arranging more flights to evacuate Americans trapped in Wuhan.

The extra flights would be laid on beginning on or about Feb. 3 and would have capacity “on a reimbursable basis” for private citizens wishing to leave Wuhan, the State Department said in a message to U.S. citizens in China on Thursday.

Those traveling on the flights would be subject to screening, health observations and monitoring, the department said.

The Centers for Disease Control and Prevention previously planned to funnel all travelers coming to the U.S. from Wuhan to one of five airports to undergo enhanced screening, But officials said Wednesday that they had revised their plan and will now screen incoming passengers at the 20 entry points where they have quarantine stations.

Health officials in Riverside County, California, “issued a quarantine order” Thursday for an individual who was evacuated from Wuhan to the United States this week and attempted to leave March Air Reserve Base, where American evacuees are being temporarily held for observation.

Many countries are curtailing flights to China, with American Airlines suspending several routes scheduled for February and March. American and Unite Airlines, British Airways German carrier Lufthansa, Israel’s El Al, Scandinavian Airlines, Egypt Air, Turkish Airlines also suspended flights, as did some in India and Kazakhstan.

Russia is closing its entire border with China, Prime Minister Mikhail Mishustin announced Thursday. Although no cases of the disease have surfaced in Russia, the country does share a 2,615-mile border with China, one of the world’s longest international borders.

The Czech Republic has suspended the issuance of visas until at least Feb. 16. “The visa centers in China are currently closed until further notice,” said Czech Foreign Minister Tomáš Petříček. “We took this step to prevent the coronavirus from spreading further.” Visas may still be issued “in exceptional and justified cases,” a statement on the Foreign Ministry’s website read.

Cruise passengers are waiting to be let off a Costa Cruises ship near Rome as local authorities test a man and woman who have been quarantined on board for potential coronavirus. About 6,000 people – 5,000 passengers and 1,000 crew members – are on the Costa Smeralda in the port of Civitavecchia, Italy.

Chinese official data now shows 8,149 confirmed coronavirus cases in the country with 171 deaths, according to state media outlets.

The figure includes nine cases in the self-governing island of Taiwan.

The number of confirmed cases Thursday afternoon was an increase of 400 from the morning. The earlier number had already surpassed the number of infections during the 2002-2003 SARS epidemic.

At least 96 cases have been recorded outside of mainland China, and three other countries have reported person-to-person transmission of the virus.

About 200 Americans evacuated from Wuhan landed in California on Wednesday. After evacuating 206 people from the city Wednesday morning, Japan is readying a second charter flight to bring more of its citizens. Three Japanese evacuees were confirmed to be infected with the coronavirus, the Health Ministry said on Thursday.

India and the Philippines reported their first cases on Thursday. South Korea has also reported two new cases, bringing its total to six.

Authorities in Australia’s Victoria State have announced a new case Thursday of the coronavirus in a middle age woman visiting from China’s Hubei Province. The latest case brings the total for Australia to nine – three alone in Victoria State.

South Korea confirmed two new cases of coronavirus infection on Thursday, one of which is believed to be the first case of human-to-human transmission in the country. The latest cases announced by the Korea Centers for Disease Control and Prevention (KCDC) brought up the national tally of infections to six.

A 56-year old man contracted coronavirus after he had come in contact with an infected person in South Korea, according to the KCDC. Another man in his 30s who had returned from Wuhan on Friday has been confirmed to have been infected by the virus.

In Manila, Philippine officials confirmed its first case of the coronavirus. The female patient, 38, came from Wuhan on Jan. 21, and has since been admitted to an unidentified government hospital. She was asymptomatic, showing no fever or other signs of illness and was admitted after reporting a mild cough.

The Philippines has stopped issuing visas upon arrival to Chinese tourists, but President Rodrigo Duterte has expressed reluctance toward a total travel ban. China is one of the Philippines’ top sources of tourists, with over a million recorded visits in 2018.

India reported its first confirmed case of the novel coronavirus, marking the arrival of the illness in the world’s second-most populous country.

The case involves a student at Wuhan University who returned to the southern state of Kerala, according to a statement from India’s Ministry of Health. The student is stable and in isolation at a hospital, the ministry said.

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The Washington Post’s Shibani Mahtani, Min Joo Kim, Regine Cabato, Joanna Slater, Carolyn Johnson, Isabelle Khurshudyan, Stefano Pitrelli, Hannah Sampson, James McAuley, Lena H. Sun, Siobhán O’Grady and Niha Masih contributed to this report.