Developed in the US, scientists at the National Institute of Allergy and Infectious Diseases in the state of Maryland appear to have taken the lead in the race to develop a cure.

Dr Peter Collins explained the reason for his team's optimism: "The nose is where the infection attacks, so it is very effective."

SARS, caused by a virus similar to the common cold, emerged in southeast Asia in late 2002 and killed nearly 800 people in 2003. Outbreaks have been controlled but the disease might re-emerge.

The US team has tested its nasal vaccine in monkeys and found that it prevented SARS infection with a single dose.

But the vaccine is effective only in children, because adults are immune to the particular virus used in the vaccine.

"We will try a different virus for adults," Collins said.

Other approaches

His team acknowledges that their approach is just one of many and others may be equally successful.

A Chinese company, Sinovac Biotech, based in Beijing, began the world's first clinical trial in May.

"The future lies in public health, not vaccines"

David Brown,
molecular biologist
University of Cambridge

Their trial involves inoculating humans with a dead version of the SARS virus. So far, four volunteers have been injected.

The vaccine appears to be safe, but the researchers do not yet know whether it will provide protection against SARS by stimulating the production of protective antibodies.

Dutch virologist Ab Osterhaus has also been developing a SARS vaccine. His, which he has tested on four ferrets, consists of SARS antibodies.

Four days after contact with the SARS virus, levels of the virus were 2000 times lower in treated ferrets than in untreated animals.

Reservations

But although progress is promising, experts warn that other disease control measures, such as minimising the spread of the disease, are important.

"The future lies in public health, not vaccines," says David Brown, a molecular biologist at the University of Cambridge.

Meanwhile, Swiss vaccine company Berna Biotech, based in Bern, announced earlier this month that it is abandoning trials of its own SARS vaccine, saying that fears of another epidemic have waned.