The head of biosecurity at the Kirby Institute, Prof Raina MacIntyre, has warned a surge in Victorian Covid-19 cases is likely to come after the state reported the first cases of community transmission in more than two months.
Three women, two in their 40s and one in her 70s, have been diagnosed with the virus and live in Mitcham, Mentone and Hallam, suburbs in Melbourne’s east. A list of exposure sites was released late on Wednesday, and was expected to be updated throughout Thursday.
It comes as New South Wales now has 160 active cases of the virus and announced 18 new cases on Wednesday, with health authorities hoping Christmas and New Year celebrations will not lead to a surge in new infections.
MacIntyre said it was most likely the Victorian cases were a result of people from NSW people who came to Victoria for Christmas celebrations.
“The appearance of these cases five days after Christmas, on the same day that NSW cases surged upward, is no coincidence,” she told Guardian Australia.
“The virus behaves predictably. Although the incubation period is 14 days, 90% of people incubate in five-to-six days, so seeing a surge five days after Christmas indicates these infections are linked to gatherings on Christmas Day. We can expect to see more cases in the next few days, and unfortunately, people infected on Christmas Day will be at their most infectious today, New Year’s Eve.
“We can therefore expect a second surge in cases between January 5 and 14.”
Victoria’s commander of Covid-19 response, Jeroen Weimar, said the active cases were a concern but that everything was being done to ensure all relevant exposure sites and close contacts were identified.
“We have been in this position before and we are deploying our full outbreak approach around these cases,” he said. “Extensive contact tracing is under way and as a result there are currently more than 40 primary close contacts that are being supported to isolate immediately.”
Weimar said that contact tracing took place throughout Wednesday night.
“At this point, our priority is on making sure we’ve got the right supports in place for the close contacts and that people are getting themselves tested,” he said.
“Now more than ever people should not let down their guard. Maintain physical distancing, practice good hand hygiene. Stay at home if you’re unwell and most of all get tested if you have any symptoms at all.”
Asked how Victorian health authorities should respond to the new cases, MacIntyre said, “It’s a tough one, given what people have been through” with an extended lockdown that lasted into October.
“The way South Australia responded a few weeks ago is a possible model – a short, sharp lockdown,” she said. “Waiting for things to get worse could result in a much longer struggle to get things under control. Tonight is a real danger of creating super-spreading.”
But Prof Lyn Gilbert, an infectious disease physician and clinical microbiologist on the federal government’s infection control advisory group, said it was too early to contemplate a lockdown in Victoria.
“One case is almost certainly linked to the Avalon cluster,” she said. “The other two, as far as I know, are still under investigation.
“Speculation is always dangerous, but I doubt they represent either lingering virus in the community or quarantine breach – only a combination of painstaking contact tracing and genomic sequencing will probably prove an answer.
“Fortunately, with only a few cases, both are much easier to achieve than they were in July. Until more is known it’s too early to contemplate a lockdown.”
Deakin University’s chair of epidemiology, Prof Catherine Bennett, said the good news is that the Victorian cases seemed to be recent, with the exposure sites listed only dating back to 26 December. She said this suggests those infected were tested within a week of being potentially infectious, and very soon after symptoms appeared.
“This not only means these people might not have been circulating for long whilst infectious, it also reduces the number of contacts to follow up,” she said.
Bennett said the 40 close contacts reported should be manageable for contact tracers.
“If investigations can identify the source upstream and reassure us that there are no missed significant transmission chains, then it should be possible to close this virus incursion down with rapid deployment of our ramped-up public health response without resorting to widespread restrictions,” she said.
“That said, some extra diligence and usual precautions, especially tonight, would be wise as there may be NSW-linked cases in our community that we are not yet aware of.”
Meanwhile the Victorian Department of Health announced that anyone who has been in or visited the Blue Mountains or Wollongong regions from 27 December will have until 11.59pm on 31 December to enter Victoria.
“Anyone intending to return to Victoria from these areas between midnight tonight and 11.59pm on 31 December must apply for a new travel permit through Service Victoria, must get tested within 24 hours of returning to Victoria, and must self-quarantine at home for 14 days from when they last left the region,” the department said in a statement.
Nobody who has visited these areas will be able to enter Victoria after then.