The first clinical trial on a test vaccine could begin in January but successful development would take far longer to complete, the WHO said in a statement on Wednesday following a meeting of international researchers at its headquarters in Geneva last weekend.

"A resurgence of SARS may accelerate the process and result in a vaccine within two years," WHO said. "If there is no big outbreak of SARS then the vaccine will follow the classical development path, and would not be ready for four to five years," it added.

The experts agreed that health authorities would be unable to
count on a vaccine if there is a resurgence of the virus later this year, after the epidemic which affected more than 8,000 people and left more than 700 dead in 32 countries until May.

Virus return

"We must be ready to manage a possible resurgence of SARS"

Lee Jong Wook, WHO Director General

The WHO has warned that the SARS virus, which thrives in similar conditions to those that lead to influenza, could return during the autumn and winter season in the northern hemisphere.

"Efforts to develop a safe and effective human vaccine against SARS and the level of international collaboration are very encouraging," said WHO Director General Lee Jong Wook.

"But in the immediate term, we must be ready to manage a
possible resurgence of SARS through the control measures that work - surveillance, early diagnosis, hospital infection control, contact tracing and international reporting," he added.