In 2004, China conducted human trials of an experimental SARS vaccine

From 2004. This piece is behind a paywall, but here is some of it:

But testing a new vaccine carries special risks. The Chinese media reports suggested the experimental vaccine is of a type known as “killed-virus” vaccines. It would entail cultivating large quantities of the live SARS virus, inactivating the virus with chemicals or with heat, and then injecting it into the body. Because the virus is dead, it can’t give people SARS, but it is hoped it will prompt an immune response that can defend people in case they are exposed to the real thing.

“The first risk would be, ‘Is it properly killed?'” said Wolfgang Preiser, a doctor at the Institute for Medical Virology at J.W. Goethe University Hospital in Frankfurt. Modern technology makes it fairly easy to ascertain the virus has been killed properly, he said. The second risk is that the animal cell-cultures used to grow the live virus may carry infectious pathogens that could be passed accidentally to people as part of the vaccine.

The third risk, Dr. Preiser said, is perhaps the greatest. With some diseases, vaccines actually can have the opposite of their intended effect: They prime the immune system to overreact, rather than to protect, the body. In such cases, vaccinated people are worse off than unvaccinated people when they are exposed to a live virus. Dengue fever is one such disease. People who suffer a mild infection with one strain of dengue are at greater risk of developing hemorrhagic fever if later they are infected by another strain.

The SARS virus, which causes a hyperimmune reaction in many patients, might be a similar kind of disease. ‘I don’t think we can rule out that,’ Dr. Preiser said.

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