Speaking from the White House lawn on Tuesday, President Obama gave an update on efforts to stop the spread of the Ebola virus in West Africa and in the U.S. (AP)

President Obama on Tuesday forcefully rejected the idea of a quarantine for medical­ workers returning from Ebola-affected­ countries, arguing that such an approach would undermine the broader effort to eliminate the epidemic .

Politicians in the United States, including the president, have come under increasing pressure to curtail the movements of medical personnel returning from Ebola-affected regions after Craig Spencer — a doctor who had been treating Ebola patients in Guinea — was diagnosed with the virus 10 days after he returned home to New York City.

While the president did not directly criticize New Jersey Gov. Chris Christie (R) and New York Gov. Andrew M. Cuomo (D) for imposing mandatory quarantines on health workers coming back from West Africa, he made clear that he thought those moves were a bad idea and were not based on the best medical information.

“We don’t just react based on our fears. We react based on facts and judgment and making smart decisions,” Obama said, just after placing a call to members of the U.S. Agency for International Development’s Disaster Assistance Response Team (DART), which has been in West Africa since the first week of August.

The notably assertive presidential response came as the country enters the final campaign stretch before next week’s midterm elections. While the president has sometimes refrained from taking on his critics, he took the unusual step of addressing the Ebola issue with reporters just before boarding Air Force One to depart for a campaign event in Wisconsin.

Calling the DART team “the strategic and operational backbone of America’s response” in the region, Obama said the effort was starting to have an impact, especially in Liberia.

“So we don’t want to discourage our health-care workers from going to the front lines and dealing with this in an effective way,” he said. “The point is this disease can be contained. It will be defeated.”

On Wednesday, Obama will convene a meeting at the White House with doctors and public health workers who have either returned from treating Ebola patients in Africa or are on their way there. The president said he convened the session not only to thank them “but to make sure that we’re getting input from them, based on the science, based on the facts, based on experience, about how the battle to deal with Ebola is going and how our policies can support the incredible heroism that they are showing.” Obama will be introduced by Kent Brantly, the missionary doctor for the group Samaritan’s Purse who became infected with Ebola in Liberia this summer but recovered after he received an experimental drug and was evacuated to Atlanta for treatment.

Obama’s comments came as the second Dallas nurse infected with Ebola has been cured and appeared at a triumphant news conference Tuesday to mark her release from Emory University Hospital in Atlanta.

“I’m so grateful to be well. First and foremost, I want to thank God,” said Amber Joy Vinson, 29, who was infected with the virus at a Dallas hospital while caring for Thomas Eric Duncan, the Liberian man who died of Ebola on Oct. 8.

Vinson added, “While this is a day for celebration and gratitude, I ask that we not lose focus on the thousands of families that continue to labor under the burden of this disease in West Africa.”

The recovery of Vinson leaves Spencer as the only person in the United States known to have an active case of Ebola. He remains isolated in what New York’s Bellevue Hospital Center said Tuesday was serious but stable condition.

This is the largest outbreak of the Ebola virus in history.

A 5-year-old boy who had been admitted with a fever has been cleared of Ebola; his symptoms were caused by a respiratory infection, the New York hospital said.

The president, who spoke to Vinson by phone Thursday, said her recovery speaks to the success the U.S. medical system has had in containing the virus’s spread. “Of the seven Americans treated for Ebola, all have survived,” he said.

The numbers are catastrophically worse in West Africa, where, according to the latest numbers from the World Health Organization, there have been more than 10,000 cases dating to the beginning of the outbreak at the end of last year, and nearly 5,000 deaths.

There are, however, scattered signs of progress. In Liberia, according to the WHO, the number of new cases has dropped in recent weeks.

“I don’t think we’ve turned the corner, but it’s better than exponential growth of new cases,” Rajiv Shah, the administrator of the U.S. Agency for International Development, told The Washington Post after a recent trip to the region. But, he added, “In Sierra Leone we are not yet seeing the kind of trend shift that we’re seeing in Liberia. There’s an urgent need to scale up the effort in Sierra Leone.”

Helen Epstein, a writer specializing in public health who has been in Liberia recently, published an online article Monday in the New York Review of Books saying the decline in new cases there is dramatic, and suggesting that “many Liberians, who at first denied the epidemic was real, have come to their senses and changed their behavior by avoiding direct physical contact with sick or dead people.”

But there is still great uncertainty about the possible reach of the virus into remote areas and rain forests where disease surveillance has been limited. The official WHO statistics show minimal progress, and disease modelers continue to be concerned.

“Hard to know what’s really going on,” said Joshua Michaud, associate director for Global Health Policy at the Kaiser Family Foundation. “Maybe it’s only people looking for good news in an ongoing crisis, maybe reporting is worse than ever and we just don’t have good understanding, maybe people are staying away from the treatment units and cases aren’t being counted, or maybe community behaviors actually have changed in the face of the mounting toll to the point where transmission has been reduced.”

The virus has a history of subsiding, then flaring up again. For example, in Kenema and Kailahun districts in Sierra Leone, new cases dropped to zero for several weeks, but then more recently the districts had 23 and 10 cases, respectively, in a single week, the WHO reported.

Samantha Power, the U.S. ambassador to the United Nations, is touring the region and on Tuesday tweeted a positive bulletin:

“Just left Sierra Leone: good news in fight vs leading cause of Ebola infection: safe burials in Freetown have gone from 30% to nearly 100%.”

The head of the World Bank, Jim Yong Kim, said Tuesday that an additional 5,000 health-care workers are needed immediately to treat Ebola victims in the three countries most afflicted: Liberia, Sierra Leone and Guinea.

Speaking in Ethi­o­pia, where he was joined by U.N. Secretary-General­ Ban Ki-moon and African Union Chairwoman Nkosazana Dlamini-Zuma, Kim pleaded with African leaders not to close their borders at a time when the stricken countries need a massive influx of health-care workers.

On Tuesday, the three largest organizations representing U.S. hospitals, nurses and physicians endorsed guidelines issued by the Centers for Disease Control and Prevention that recommend state and local officials closely monitor but not quarantine returning health workers based on their level of exposure to Ebola.

Meanwhile, the Joint Chiefs of Staff made a formal recommendation Tuesday to Defense Secretary Chuck Hagel that he require all U.S. troops returning from West Africa to be subjected to 21 days of quarantine-like conditions. If approved by Hagel, the policy would essentially extend to all branches of the armed forces a decision made Monday by Gen. Ray Odierno, the Army chief of staff, to put several dozen soldiers returning from West Africa in isolation for 21 days at a base in Italy.

Speaking to reporters Tuesday, White House press secretary Josh Earnest said the civilian and military policies differed because there are “a couple of dozen health-care workers a week who are returning to this country from West Africa,” compared with “thousands of military service members who have been or will be deployed to West Africa to carry out the mission that the president ordered.”

“It would be wrong to suggest that it would make the American people safer to apply this military policy in a civilian context,” Earnest said. “The science would not back that up.”

According to Capt. Carter Langston, an Army spokesman in Monrovia, there are now more than 700 U.S. personnel in West Africa.

Craig Whitlock contributed to this report.