Two members of a West Melbourne family who visited New South Wales last month before testing positive for Covid-19 have been found to have the Delta variant of Covid-19.
It’s the first time the variant – first identified in India – has been found in the community in Australia.
So how does the Delta variant differ from other strains of coronavirus?
The World Health Organization has begun using letters of the Greek alphabet in its designation of new Covid variants, and the Delta variant, also known as B.1617.2, is the name given to the variant first detected in India in October 2020.
The WHO says it has now been detected in 62 countries and is becoming the dominant variant in several countries including Nepal, Bangladesh, and Sri Lanka. In the United Kingdom it is estimated to be the variant in 75% of cases.
In Australia, all of the more than 60 cases in Melbourne’s outbreak have been linked to the other variant first detected in India – the Kappa variant – except for the two West Melbourne cases.
Victorian health authorities said the Delta variant was discovered after examining the genomic sequence of the virus detected in two cases in a family of four that travelled to NSW in late May. They visited Goulburn and Jervis Bay before becoming symptomatic and getting tested.
The variant was first detected in a child in grade five in a school in North Melbourne, and it is likely it was child-to-child transmission.
There are now seven cases across two families linked to this cluster, after two adults and a child tested were reported as positive cases on Friday. Another child is an indeterminate case.
About 70% of the 300 identified close contacts of the family who have been isolating have returned a negative test result.
The source of the original transmission remains unknown. Victoria’s chief health officer, Prof Brett Sutton, said health officials in Victoria are hunting down any leads, by looking at sequences of the virus detected in hotel quarantine, through airlines, and through maritime, diplomatic and other ways people have returned to Australia.
“We have to explore all avenues,” he said. “We have to be clear who the likely first case in this cluster is and then to go through a really forensic process of understanding everywhere they have been and obviously all of the testing of those people they may have been in contact with, including blood tests of people have recovered from illness”
Honorary senior research fellow at the George Institute for Global Health, Prof Alexandra Martiniuk, said variants were more likely to occur in countries with large numbers of cases. Martiniuk said Delta is one of four so-called variants of concern where the variation either increases transmissibility, increases virulence, has a more severe presentation in hospital or decreases the effectiveness of the public health response.
Kappa is a variant of interest, which is still more infectious than other strands but hasn’t been observed to have as high community transmission as Delta and other variants of concern.
“Delta is a more concerning variant than the Kappa variant,” she said. “Kappa is currently listed as a variant of interest – not as concerning as Delta at this point.”
Sutton said he was concerned about the very high level of transmissibility, plus the anecdotal reports that it was more transmissible between children than other variants.
It’s too early to say.
“The severity or duration of disease compared with ‘original’ SARS-COV2 for the Delta variant is currently not yet known, [there’s] not enough research yet,” Martiniuk said. “The other variants of concern have likely increased severity and death.”
In England where 38,805 cases were sequenced, they found the Delta variant was associated with a 2.61 times higher risk of hospitalisation within 14 days than the Alpha variant.
Vaccines seem to have an impact on transmission. In the UK, it was reported that 75% of the Delta cases were people who were unvaccinated, with just 3.7% of people who were fully vaccinated getting the Delta strain. A total of 5% of those hospitalised with the Delta variant were fully vaccinated.
Australia’s chief medical officer, Prof Paul Kelly said the efficacy of AstraZeneca against this particular variant was yet to be seen.
“There has been some work in the UK which suggest there may be a lower efficacy of AstraZeneca but it is not zero and that is preliminary laboratory work and we have to wait for the real world experience which only comes when we have large outbreaks and I’m sure we will not be having those in Australia.”
Sutton said the identification of the Delta variant in the community would not change plans immediately, as close contacts connected to the family were isolating and getting tested. But he said it was important to find the source, and whether there were more cases linked.
“We need to understand where it has come from. That means there are unidentified upstream cases, whether they are in Victoria or elsewhere is to be determined.”