A possible vaccine against the Sars virus has passed the first stage of testing in monkeys.
The jab could be used to protect health workers
US scientists, writing in the Lancet journal, showed that the monkey immune system responded to the jab, and their blood then killed Sars in a test tube.
However, the researchers have yet to show that immunised monkeys can fight off a real Sars infection.
The Sars coronavirus is thought to have killed almost 800 people earlier this year - one in ten of those infected.
Separate efforts are continuing in research labs around the world to find a working Sars vaccine.
Although there have been no cases of Sars in the community since early this year, experts predict that another strain of the virus could emerge this winter.
Symptoms include a rapidly worsening pneumonia and high temperatures - which mean many need help breathing while their bodies fight the illness. A combination of antiviral drugs and steroids.
There is unlikely to be mass immunisation in the event of the virus returning, but at-risk health workers and others in contact with sick patients may get the jab.
Most vaccines are made from either weakened, live copies of the virus itself, or dead viruses - neither can cause an infection, but stimulate the immune system to "remember" the intruder and react aggressively when a real infection threatens.
The US team, from the University of Pittsburgh and the Centers for Disease Control in Atlanta, made their vaccine a different way.
They took another kind of virus - an adenovirus, which usually causes respiratory tract infections such as colds - and inserted little bits of the Sars virus, including protein fragments from the distinctive spikes that form the "corona".
These were then injected into the muscles of rhesus macaque monkeys, and a booster jab given four weeks later.
Target: The coronavirus
The blood of the monkeys was checked to see if there were any signs of immune response to the viral fragments in the vaccine, and found clear traces of anti-viral activity.
In addition, when Sars virus was mixed with blood from the monkeys, the immune cells and proteins within it were able to neutralise it.
The researchers say their work "holds promise" for the development of a protective vaccine.
Dr David Cavanagh, who researches the coronavirus at the Institute of Animal Health in Compton, Berkshire, said that it was possible that this approach might yield a useful vaccine.
He said: "The vaccines that do the best job are generally live vaccines, with weakened viruses, because they grow in the right places, so the immune response is triggered in the right place.
"There is some Australian research showing that this approach, using a bird adenovirus in chickens found that between 90% and 100% of the birds resisted 'challenge' from infectious bronchitis virus, so that is encouraging, and suggests this could work.
"What we are waiting for now is to see if monkeys given this vaccine can resist a challenge from Sars."