COVID cases have spiked in Victoria and Queensland amid a blow to hopes for one of the most promising vaccines undergoing trials.

Victoria remains the worst-hit state, with coronavirus cases jumping to 76 on Wednesday, while Queensland had eight new infections – its highest number in weeks.

NSW reported nine more infections on Wednesday, the same number it had on Tuesday.

It came as trials of the Oxford University and AstraZeneca coronavirus vaccine were halted after a participant experienced a serious adverse reaction.

Australia has ordered millions of doses of the AstraZeneca vaccine, which was expected to be rolled out in 2021, if trials proved successful.

The company said in a statement on Tuesday its “standard review process triggered a pause to vaccination to allow review of safety data”.

AstraZeneca didn’t reveal any information about the possible side effect except to call it “a potentially unexplained illness”.

National deputy chief medical officer Nick Coatsworth said the delay did not necessarily mean the vaccine deal was dead, but the adverse reaction needed to be investigated.

AstraZeneca said it was possible the problem in the trial was a coincidence, adding illnesses of all sorts can arise in studies of thousands of people.

“We are working to expedite the review of the single event to minimise any potential impact on the trial timeline,” the company said.

Scott Morrison toured AstraZeneca’s Sydney labs in August to promote the vaccine deal.

On Monday, Prime Minister Scott Morrison and Health Minister Greg Hunt said the federal government had struck a deal with manufacturer CSL to produce millions of doses of two promising COVID vaccine candidates – one was AstraZeneca’s, the other from the University of Queensland.

Elsewhere, Victoria’s virus toll rose by 11 on Wednesday. They were a woman in her 60s, two men and three women in their 80s and two men and three women in their 90s. Nine were linked to outbreaks in aged care.

The coronavirus has now claimed the lives of 694 Victorians, while the national toll is 781.

Wednesday’s 76 new infections was the highest for Victoria since Saturday. It reversed a welcome recent trend of lower numbers as Melbourne heads towards the daily average of 30-50 cases that has been set as a benchmark for its path out of COVID restrictions.

Premier Daniel Andrews said Melbourne’s rolling 14-day average had fallen to 74.5 despite, despite Wednesday’s jump.

Victoria’s chief health officer Brett Sutton has previously acknowledged that Wednesdays often bring a spike in infections.

Meanwhile, Queensland Premier Annastacia Palaszczuk said the surge in cases in the Sunshine State was concerning, but she urged residents not be alarmed.

“I want to assure Queenslanders that although that number is our highest daily tally for some time, each of those people diagnosed is related to existing cases,” she said.

“This is not a time for alarm, this is a time for thanks that our testing system is so professional.”

Five of the eight cases confirmed on Wednesday are people from a single family, linked to the Queensland Correctional Services Academy at Wacol. The others are linked to the Ipswich Hospital Cluster.

Of NSW’s new cases, seven are linked to known outbreaks. They include two linked to the CBD cluster and five more in the cluster at the Liverpool and Concord hospitals.

One is in hotel quarantine, while the remaining case is still being investigated.

Premier Gladys Berejiklian urged NSW residents to remain alert to the dangers of the coronavirus.

“I want to emphasise not only the importance for all of us to be on our guard when it comes to the virus but also to highlight, given some of the cases that we experienced this week, how absolutely contagious the virus is,” she said.