Two American nurses were declared cured of Ebola and one - Dallas-based Nina Pham hugged President Barack Obama at the White House to prove it.

But the states of New York and New Jersey ordered mandatory quarantine for medics who had treated victims of the disease in West Africa.

Steps include mandatory quarantine 21 days of any individual who has had direct contact with an Ebola patient while in Guinea, Liberia or Sierra Leone, including medics who treated Ebola patients.

Additionally, anyone who has travelled to the affected regions but not had direct contact with an Ebola patient will be actively monitored by public health officials and quarantined if necessary.

Europe's main stock markets fell yesterday over concerns about New York's first case, in a doctor who tested positive after returning from treating sufferers in Guinea, one of the countries at the epicentre of the world's worst outbreak of the disease.

The search for an effective vaccine to fight the disease took on fresh urgency as the WHO said several hundred thousand doses could be available in the "first half" of 2015.

"All is being put in place to start efficacy tests in the affected countries as early as December," WHO assistant director general Marie-Paule Kieny said.

Kieny's comments came after closed-door talks to try to find a vaccine to beat a disease that has killed almost 4,900 people and ravaged the west African nations of Guinea, Liberia and Sierra Leone.

Experts are pinning their hopes on the experimental vaccine rVSV, with doses arriving in Geneva for a new round of trials, and ChAd3, made by Britain's GlaxoSmithKline.

Five other potential vaccines are in the pipeline.

Whichever proves effective in trials, WHO hopes to send huge numbers of doses to Africa for "real-world" tests.

"The pharmaceutical companies developing all these vaccines are committing to ramping up the production capacity to millions of doses to be available in 2015," said Kieny.

There is currently no licensed cure for Ebola, which is transmitted through close contact with the bodily fluids of an infected person or someone who has died from the disease.

New York's mayor said America's biggest city was fully equipped to handle Ebola as authorities moved to shut down fears of the virus spreading after a 33-year-old doctor, Craig Spencer, became the first American case of the virus outside Texas.