An experimental Ebola vaccine tested on 20 volunteers appears to be safe and producing the immune response expected within four weeks of receiving the dose.

Half of the test group received a higher-dose shot, and those people produced more antibodies, says a study published in the New England Journal of Medicine.

Some people also developed a different set of virus-fighting immune cells, named T cells, doctors found.

Research on monkeys had also noticed such a combination response, reports AP.

Calling it "a promising factor," Anthony Fauci, director of NIH's National Institute of Allergy and Infectious Diseases, which led the vaccine work, said the response was comparable to what had produced protection in the animals.

The researchers reported no serious side effects other than high fever which subsided in a day. A booster shot may be needed, say experts, going by the results in monkey trials.

The NIAID is working with vaccine maker GlaxoSmithKline to develop the vaccine, reports NBC News.

It uses a common cold virus that normally infects chimpanzees but does not cause any symptoms in people. When genetically engineered with a small piece of the Ebola virus, it is expected to trigger the immune response against the Ebola virus.

Additional safety studies are under way in the US and elsewhere. A different Canadian-made vaccine also has begun small safety studies.

Meanwhile, the WHO has called for rapid, safe and simple diagnostic tests saying that efforts to contain the Ebola outbreaks in West Africa are currently hampered by cumbersome, slow and complex diagnostic tests that pose a number of additional logistical challenges.

The standard test method using a RT-PCR reaction provides accurate results when performed by trained staff. But each test requires a full tube of blood, takes from two to six hours, and costs around $100.

The virus has claimed over 5,600 people in West Africa, most of them in Guinea, Liberia and Sierra Leone.