A SARS vaccine could be used among high-risk groups in China in the event of a large-scale outbreak again this spring, say experts.
The inactivate vaccine was produced last May following a year of intense research to find a vaccine for the virus which sparked a global health scare when it emerged in early 2003.
Trials among 36 volunteers have proved effective and safe in the first-phase human tests begun on May 22, 2004, said Yin Weiping, managing director of Beijing-based Sinovac Biotech Co Ltd which has produced the vaccine.
Yin heads China's SARS vaccine development group working with experts from Beijing Sinovac, the Chinese Center for Disease Control and Prevention and the Chinese Academy of Medical Science.
Before early December 2004, antibodies, without obvious side effects, had been found in all volunteers, who had the test vaccine, said Yin.
His laboratory currently has a number of batches of inactive vaccine - one made from viruses or bacteria that have been killed through physical or chemical processes - and can produce more if necessary.
Although the vaccine has been produced and proven effective primarily, "we cannot sell it to the public at present even if they wanted to buy it," said Yin.
Normally, only after a vaccine has passed the third-round of human trials in fighting an active virus which breaks out naturally will it be provided to the public widely, he explained.
However, in the event of a sudden and widespread SARS outbreak, some high-risk groups, such as doctors might be immunised ahead of completion of the second and third round trials, said Dr Lin Jiangtao of Beijing's Sino-Japanese Friendship Hospital, where the first tests were conducted.
The memory of the spring of 2003 when SARS struck is still fresh in the minds of many.
Between March and June 2003 some 5,327 people on the Chinese mainland, most of whom were doctors and nurses were infected. A total of 349 people died.
With no vaccine yet available, the recurrence of SARS kept the public on tenterhooks in the spring of last year.
The second-round of tests will involve further experimental verification in many aspects, such as dosage and schedule for injecting the vaccine to gain a better understanding of it and how it can best be used.
A date for beginning the second-round of tests has not been fixed, while the third-round of trials will necessarily involve hundreds of volunteers in the event of another large-scale SARS outbreaks, Yin Weiping noted.
Those in the first round trials only received an antibody which has not been proven effective in fighting an active SARS virus.
"It is not possible for us to use an active virus on those immunized to test whether the vaccine is effective," said Lin, who leads the clinical testing in the hospital.
Research has shown that the antibody brought about by the vaccine in animals is resistant to attacks by the active SARS virus, a coronavirus.
Moreover, any new vaccine poses risks before it proves itself against active virus outbreaks, said Yin Hongzhang, a division director of the State Food and Drug Administration.
One major potential risk is that people who are vaccinated might become even more vulnerable than those who are not, said Yin.
Currently, experts are following up people who took part in the first-round test to record the reaction of their internal organs and blood post-immunisation, said Lin.
The follow-up records of Lan Wanli, the first man to be vaccinated on May 22, 2004, was completed after 210 days.
It showed he had suffered no untoward side-effects and had developed an immunity to the virus, said Lin.
The last of the 36 volunteers vaccinated last August, will be monitored until March, 2, 2005.
A 210 day period is considered by scientists the set period for assessing a vaccine's efficacy.
These records provide valuable information for the second-phase human trials, which will involve 300 volunteers, said Yin.
"Compared to the time when there was no SARS vaccine, we now feel much less disquiet with spring approaching, because we now have a powerful weapon," said Dr Lin.
His remark was echoed by one of the volunteers, Lan Wanli, 23, a postgraduate student at Beijing University of Chemical Technology.
He experienced no untoward side-effects after being vaccinated, and was reassured by the fact he had received the anti-SARS jab.
"It is a worthy cause for me to volunteer for the vaccine test although there are lots of risks, the most serious one is that I could be infected with the virus if the vaccine is unsafe," Lan said.
As a human guinea pig for the SARS trials Lan underwent 14 hospital examinations and a series of blood tests.
Several days after China reported the results of its first-round testing, researchers at the National Institute of Health (NIH) in the United States began clinical trials of a SARS vaccine, Yin revealed.
(China Daily January 15, 2005)