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By Mike Cherney 

SYDNEY -- A Covid-19 vaccine candidate in Australia has been scrapped because recipients returned false positives on certain HIV tests, underscoring the difficulties scientists face in rapidly developing an inoculation for the coronavirus.

The vaccine candidate, called v451, was being jointly developed by the University of Queensland and CSL Ltd., an Australia-based biopharma company that also runs blood-collection centers in the U.S. The Australian government had agreed to buy 51 million doses.

The episode illustrates why governments have sought access to multiple vaccines and more doses than needed for their populations. Some vaccines might not prove effective, adverse reactions might arise and manufacturing constraints could limit how many doses can be produced.

The U.K. already has granted emergency authorization to distribute the Pfizer Inc. and BioNTech SE vaccine, and the U.S. could do so shortly. In Australia, however, community transmission of the virus is negligible after international borders were shut and stringent local lockdowns were imposed, so officials say there was no need for a similar emergency-use authorization.

"We can take our time," Australian Health Department Secretary Brendan Murphy said. "We're in a good position because we've controlled the virus."

The v451 vaccine relied on "molecular clamp" technology, which stops spike proteins on the coronavirus from uncoiling, according to CSL. Recipients develop antibodies to the coiled shape. The vaccine, however, involved the use of an HIV protein, causing some recipients to generate the antibodies that created the false positives on the HIV tests.

Researchers said there is no possibility the vaccine causes an actual HIV infection, and follow-up tests confirmed no HIV virus was present in the recipients. In addition, they said there were no serious adverse events or safety concerns in the 216 people who participated in the Phase-One trial, and that the vaccine created a robust response to the coronavirus.

"Many readers will look at this and say, 'Oh my God, these vaccines aren't safe,' " said Nancy Baxter, a clinical epidemiologist and head of the Melbourne School of Population & Global Health at the University of Melbourne, who wasn't involved in the trial. "It's super important that this wasn't anything to do with the safety of the vaccine."

The researchers said it would take another 12 months to re-engineer the vaccine and fix the issue, which would have taken too long. Rolling out the vaccine in its current form would have required significant changes to HIV- testing procedures. That prompted authorities to decide it wasn't worth progressing the vaccine to a more advanced clinical trial.

The v451 vaccine was one of four that the Australian government had agreed to buy if proven effective. Australian officials said Friday that they hadn't bet on all four vaccines getting through the approvals process.

"If that had occurred, that would have been truly extraordinary," Australian Prime Minister Scott Morrison said. "That's why we spread our risk."

Mr. Morrison said Friday that Australia had increased its orders for two of the vaccines still under consideration. One of those vaccines, from Oxford University and AstraZeneca PLC, is being manufactured by CSL in Australia, reducing supply-chain risks. In total, Health Minister Greg Hunt said Australia had access to more than 140 million doses, more than enough to cover a population of roughly 25 million.

Australian officials have said they expected vaccines to be approved for use early next year and the first inoculations of vulnerable populations to occur in March. Mr. Hunt said Friday that dropping the v451 vaccine would enable manufacturers to speed up production of the other vaccines, meaning that a nationwide vaccine rollout could be completed more quickly than anticipated.

Researchers knew a possibility existed that the v451 vaccine candidate could create false HIV positives, though the risk was seen as being extremely low at the start of the study, Dr. Murphy said. During the Phase-One trial, researchers were surprised by the prevalence of false positives, he said.

"It was likely to be a promising vaccine, it was likely to work," Dr. Murphy said. "But we knew that we didn't want to have any issues with confidence."

Write to Mike Cherney at mike.cherney@wsj.com

(END) Dow Jones Newswires

December 10, 2020 19:42 ET (00:42 GMT)

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