• Australia is quitting work on the University of Queensland’s vaccine candidate after trial participants developed antibodies that would show false positives on HIV tests
  • Prime Minister Scott Morrison is emphasising that the country has plenty of other vaccine candidates available
  • Shares in CSL, which was to have made the vaccine, have dropped to a one-month low

CSL (ASX:CSL) shares are down nearly three per cent to a one-month low after Australia’s largest biotech company abandoned the COVID-19 vaccine candidate it was developing with the University of Queensland.

The phase 1 trial involving 216 participants showed some had generated antibodies that would cause a false positive on HIV tests, CSL said.

There were no safety concerns but widespread use of the vaccine would necessitate significant changes to well-established HIV screening procedures, the company said.

To stabilise the vaccine researchers had used a small portion of the gp41 protein from the HIV virus, CSL said.

Unexpectedly, the trial participants generated enough antibodies to the protein that certain HIV tests would have returned a false positive, CSL said.

“The modelling at the time thought it was a very low theoretical risk,” Dr Brendan Murphy, secretary of the Department of Health, told journalists. “So it was very unexpected.”

“There is no possibility the vaccine causes infection, and routine follow-up tests confirmed there is no HIV virus present,” CSL said.

It’s not clear for how long the trial participants will falsely test positive for HIV using those gp41 assay tests, but their antibody levels are already falling.

The University of Queensland’s vaccine co-lead, Professor Paul Young, said the core technology had passed a major clinical test, in that it was safe well-tolerated and showed a strong virus-neutralising effect. It should be a “robust platform” for future vaccine development, he said.

“I emphasise it was excellent research, it was a good platform, and it was likely to be an effective vaccine at preventing coronavirus,” Dr Murphy said.

“But we cannot risk public confidence. We just can’t.”

Plenty of other vaccines

Prime Minister Scott Morrison said that while Australia had earlier identified four vaccine candidates it thought might be successful, “at no stage, can I assure you, that we believed that all four of those vaccines would likely get through that process … that’s why we spread our risk.”

CSL said it would make an additional 20 million doses of the Oxford/AstraZeneca vaccine, in addition to the 30 million doses already being manufactured. AstraZeneca has also agreed to ship Australia 3.8 million doses, giving the country a total of 53.8 million doses.

Australia has also has agreements to buy 51 million Novavax doses, 10 million Pfizer vaccine doses, and 25.5 million doses from the World Health Organization’s COVAX initiative, the Prime Minister said. All three vaccines require two doses.

“I think what this demonstrates is the effectiveness of our strategy,” Morrison said. “And what we can do is vaccinate our population twice over.”

CSL said it doesn’t anticipate the announcement would change its financial guidance for FY2021.

At 11.14am, CSL shares were down 2.9 per cent to $292.65, their lowest level since early November.