With three cases of Ebola diagnosed in the US but dozens of people being monitored in case they contract the disease, President Barack Obama urged Americans yesterday not to give in to “hysteria” about the spread of the virus.

Obama also made plain he is not currently planning to give in to demands from some lawmakers for a ban on travellers from the worst-hit countries.

“We can’t just cut ourselves off from West Africa,” Obama said in his weekly radio address. “Trying to seal off an entire region of the world - if that were even possible - could actually make the situation worse,” he said.

The worst Ebola outbreak on record has killed more than 4,500 people, most of them in the West African countries of Liberia, Sierra Leone and Guinea.

Obama, whose approval rating is already low, has been criticised over his administration’s handling of Ebola. He held a flurry of meetings on the issue in recent days and on Friday appointed Ron Klain, a lawyer with long Washington experience, to oversee the effort to contain the disease.

Republicans questioned why he did not pick a medical expert.

“I hope he (Klain) is successful in this. I think it’s a step in the right direction, but I just question picking someone without any background in public health,” Republican Representative Ed Royce, chairman of the House Foreign Affairs Committee, told CNN yesterday.

The Obama administration is not alone in facing criticism. The World Health Organisation has been faulted for failing to do enough to halt the spread of Ebola since the outbreak was first detected in March.

Yesterday, the agency promised it would publish a full review of its handling of the crisis once the outbreak was under control, in response to a leaked document that appeared to acknowledge that it had failed to do enough.

There is no cure or approved vaccine yet for Ebola but pharmaceutical companies have been working on experimental drugs. Canada said yesterday it would ship 800 vials of its experimental Ebola vaccine to the WHO in Geneva, starting tomorrow.

The WHO, in consultation with health authorities in the countries most affected by Ebola, would decide on how the vaccine will be distributed and used, the Public Health Agency of Canada said in a statement.

The vaccine was undergoing clinical trials at Walter Reed Army Institute of Research in the US, it said. Iowa-based NewLink Genetics Corp holds the commercial license for the Canadian vaccine.

Obama sought to put the extent of the disease in the US in perspective. “What we’re seeing now is not an ‘outbreak’ or an ‘epidemic’ of Ebola in America,” he said. “This is a serious disease, but we can’t give in to hysteria or fear.”

A rash of Ebola scares has hit the country in recent weeks. In one such incident, a woman vomited in a parking lot at the Pentagon on Friday, triggering authorities to send in a HazMat team and shut off part of the military complex before concluding she did not have the virus.

Americans’ faith in the medical system and in authorities’ ability to prevent the disease from spreading in the US was jolted by a series of mis-steps after a Liberian visitor to Texas was initially not diagnosed with the illness by a Dallas hospital in late September.

The man, Thomas Eric Duncan, was admitted to Texas Health Presbyterian Hospital several days later and diagnosed with the disease. Two nurses who were part of the team caring for Duncan, who died on Oct. 8, contracted Ebola. Amber Vinson is being cared for at Atlanta’s Emory University Hospital, while Nina Pham is being treated at the National Institutes of Health (NIH) just outside Washington.

Pham, whose condition was described as “fair” on Friday, continues to rest comfortably at NIH, hospital spokesman John Burklow told Reuters yesterday.

A chain of more than 100 people who had contact with either Duncan or the sick nurses are being monitored in case they develop the disease, which has an incubation period of up to 21 days and is transmitted by contact with a sick person’s bodily fluids.

The White House said late on Friday it would send senior personnel to Dallas to help federal, state and local officials there trying to identify and monitor people who came in contact with the three people who fell sick with Ebola.

Those being monitored include a lab worker at the Dallas hospital, who is not ill but is in isolation at sea: in her cabin on the Carnival Magic cruise ship. The lab worker, who has not been named, did not have contact with Duncan, but may have come in contact with test samples.

The lab worker’s presence on the ship caused Mexican authorities to deny docking at the Mexican port of Cozumel on Friday.