What does presence of the Delta variant mean for Australia?

‘It is more infectious than the Alpha variant [formerly B.1.1.7], which is already 50–100% more infectious than the strain that caused Victoria’s second wave last year.
 
‘If we do not identify every contact and new case, it would be a more difficult outbreak to control.’
 
That is infectious diseases expert Professor Raina MacIntyre speaking to newsGP about the detection of the Delta variant of COVID-19 in Victoria.
 
Formerly known as B.1.617.2, it has become the dominant strain in both India and the UK, leading the World Health Organization to classify it as a ‘variant of concern’.
 
Its discovery in Victoria was announced on Friday, after genomic testing found members of a Victorian family had tested positive to the variant after travelling to regional New South Wales.
 
NSW’s Ministry of Health has confirmed the infections are not genomically linked to known cases in NSW.
 
Authorities have so far not been able to link the cases in the Victorian family to other Delta cases previously identified.
 
Victoria’s Chief Health Officer Professor Brett Sutton said it remains possible that the family became infected while travelling interstate, but the dominant theory is that the variant was transmitted between two Grade 5 students at school.
 
‘We suspect so, but we need to look further. But that’s the likely transmission at the moment,’ Professor Sutton said.
 
‘We know this family travelled to Jervis Bay [NSW] and we are examining who is the likely index case in this family, and therefore trying to trace back where this variant has been picked up.
 
‘We’re working with our New South Wales, ACT and Commonwealth counterparts in that regard.
 
‘We will look at all other sequences, re-sequenced to the fullest extent possible across Australia to see if there are any potential linkages to known cases and that includes those who have come through formal quarantine but also anyone else, maritime, airline, diplomatic.’
 
So far, the Kappa variant, formerly known as B.1.617.1, has been at the centre of Victoria’s current outbreak.
 
Stuart Turville, an Associate Professor in the Immunovirology and Pathogenesis Program at the Kirby Institute, describes the Delta variant as ‘a genetic cousin to Kappa’ – the key difference being that the Delta variant has a fitness gain that enables the virus to better bind cells.
 
‘Where Kappa had a change called 484q, this has 478k. If we remember back to our second wave, we had a similar virus called variant 20F. It also had a similar change called 477n,’ he said.
 
‘Changes in these regions [477 and 478] are observed to increase affinity to the primary receptor ACE2. In the lab under controlled conditions, we do see Delta to be approximately 1.4 times fitter than Kappa.
 
‘Whilst this is a laboratory observation, the displacement of Kappa by Delta in India does support it to be a fitter variant in populations where vaccine immunity is low.’
 
Data from Public Health England released this week shows the Delta variant carries 2.61 times the risk of hospitalisation within 14 days compared with the Alpha variant.
 
The Delta variant also appears to be more transmissible among children, with 140 outbreaks in schools and educational settings in the UK.
 
‘It does appear to be the most significant [variant] in terms of transmissibility,’ Professor Sutton said.  
 
‘There isn’t much information about severity of illness with this variant, although there are some anecdotal reports of greater severity of illness in children, as well as potential increased transmissibility in children. So we’ve got concerns for that reason.’
 
While effectiveness of AstraZeneca and Pfizer vaccines does appear to diminish against the variant, experts say recent UK data is reassuring, showing that both offer relatively good protection after two doses.
 
‘The effectiveness of one dose of Pfizer or AstraZeneca is only 33% against B.1617.2 [Delta]; but this rises to 88% after two doses for Pfizer and 59.8% after two doses of AstraZeneca,’ Professor MacIntyre said.
 
‘This means it does have some resistance to vaccines, although not as much as the South African variant [Beta].
 
‘There is also the possibility of evasion from vaccines for the B.1617.1 [Kappa].’
 
Professor MacIntyre says the confirmed presence of Delta in the Australian community adds further urgency to the vaccine rollout, which she believes also needs to include children, but Pfizer’s 21-day waiting period between doses (compared to AstraZeneca’s 12 weeks) makes it a preferred vaccine option.
 
‘Very few Australians are vaccinated, and even fewer fully vaccinated,’ she said.
 
‘These are reasons why people should get vaccinated as soon as possible, and why a three-month gap to wait for your second dose may end up being costly during an epidemic.
 
‘And we also need to start formulating a vaccine strategy for children.’
 
Dr Turville agrees.
 
‘Vaccination is our key defence and until we have higher rates, we need to treat this variant and all variants like we have done in 2020,’ he said.
 
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