] SARS is caused by a new member of the coronavirus family,
] which also causes some forms of the common cold. Some
] scientists have noted that the rapid mutations shown by
] cold viruses have prevented the development of a vaccine,
] and that the same may be true for SARS. The mutations
] change the surface proteins, known as antigens, which
] elicit the immune response.

New Scientist - SARS vaccine tests begin in monkeys