Understanding what happened to the CSL vaccine

On Friday, pharmaceutical giant CSL announced the phase two and three clinical trials of their COVID-19 vaccine will not go ahead, as some trial participants showed a false positive result for HIV.

What’s a false positive?

A false positive means that whilst the test indicates trial participants had HIV, they actually didn't.

The CSL vaccine generates a particular protein that interferes with the way in which HIV is diagnosed - none of the participants who returned HIV positive tests actually have HIV.

This risk was anticipated before the trial began, and participants were informed this may occur.

So if it doesn't actually present a health risk, why is the trial being terminated?

Ultimately, the Federal Government, Australia's health and science agencies, and CSL, made the decision to terminate the trial to uphold public trust in Australia's vaccination program.

Officials feared that HIV false positives in vaccinated people would lower the number of people who came forward to receive the vaccine.

"It was looking like it was going to make antibodies, and it probably would have worked very well as a vaccine, but we can't have any issues with confidence, and we are – as a nation now, with a good portfolio of vaccines – able to make these decisions to best protect the Australian people."

Dr Brendan Murphy, Secretary of the Department of Health, speaking on Friday

What happens now?

The Australian Government backed five separate clinical trials to produce a COVID-19 vaccine for Australians. Speaking today, Prime Minister Scott Morrison said that his Government anticipated that at least one trial would not be successful.

Because of the termination of the CSL trial, the government will divert their investment to other clinical trials, which means the AstraZeneca and Novavax vaccines will be produced faster. According to the Government, all Australians will have access to a vaccine by at least the end of 2021.

Couldn't CSL just fix the vaccine?

According to Dr Andrew Nash, the chief scientific officer of CSL, yes. But it would have taken at least 12 months, and further trials, and that approach would be inconsistent with the Australian Government's broader aim of making a safe vaccine as quickly as possible.

Instead, CSL will use their new production capacity at their Melbourne warehouse facility to assist in the mass production of other vaccines.