Explainer: What we know about the Delta variant so far


Greater Sydney is in lockdown for two weeks to halt the spread of the Delta COVID-19 variant as cases crop up in other Australian states.

What is the Delta variant?

The Delta variant of the SARS-CoV-2 virus, scientifically known as B.1.617.2, was first detected in India in October, 2020. It has since been recorded in more than 80 countries and is the dominant strain of the virus in India and Britain. Under the World Health Organisation's (WHO) variant characterisation system, Delta is one of the four variants that are classified as "variants of concern". The Delta variant is the COVID virus strain in NSW's recent Bondi cluster outbreak.

Why is everyone talking about it?

On June 26, Greater Sydney was put under stay-at-home orders due to the rising number of Delta variant cases linked to the Bondi cluster. Of the 149 locally acquired cases since June 16, 141 are linked to the Bondi cluster.

While NSW has previously experienced COVID-19 outbreaks, notably the Northern Beaches cluster in December 2020, the new outbreak of the Delta strain has a much greater rate of transmission.

The NSW Premier, Gladys Berejiklian describes this as "perhaps the scariest period that NSW is going through" since the pandemic began. Chief Health Officer, Dr Kerry Chant said the Delta variant has close to 100% chance of transmissions within households.

What is a 'variant of concern'?

WHO classifies strains of the COVID-19 virus as "variants of concern" when they match one or more of the following criteria at a level of global public health significance:

  • Increase in transmissibility or detrimental change in COVID-19 epidemiology;
  • Increase in virulence or change in clinical disease presentation;
  • Decrease in effectiveness of public health and social measures or available diagnostics, vaccines, therapeutics.
The potential increased transmissibility among children is a concern and will 'give us cause to strengthen our guidelines in relation to schools'.

How does it compare to other strains?

There are three COVID-19 variants present in Australia: Alpha, Delta and Kappa. Alpha and Delta are classified as variants of concern, Kappa is classified as a variant of interest.

The Kappa variant was first detected in India in October 2020 and was the strain at the centre of Victoria's recent outbreak. Alpha originated in the United Kingdom last year and has been reported as 50 per cent more contagious than the original virus. However, researchers in the UK have found that the Delta strain could be 60 per cent more contagious than the Alpha strain. The risk of hospitalisation with the Delta variant was double that of the Alpha variant, according to a study in the Lancet.

How did it enter NSW?

The first recorded case of the Delta variant in NSW was a limousine driver in his sixties from the Eastern Suburbs. He tested positive on June 16. While there is no conclusive evidence as to how the limo driver contracted the Delta variant, the most likely scenario is that he caught it while transporting an international airline crew.

What is 'fleeting contact'?

Can I get the Delta variant by walking past a stranger? WHO acknowledges all strains of the COVID-19 virus are airborne and can be transmitted through particles suspended in the air. The Delta variant is thought to have the highest level of variant transmission and can be contracted with "scarily fleeting" contact, according to the NSW Premier. CCTV footage from Myers Bondi Junction revealed only fleeting contact between a COVID-Delta-positive person and a man in his 50s who walked by him and later also tested positive.

How effective is the vaccine against Delta?

There is some evidence to suggest theDelta variant may be slightly more resistant to vaccinations than other variants, however, the vaccine is still one of the most effective ways of preventing its spread and of people who contract it getting seriously ill. At the recent West Hoxton birthday party superspreader event, 24 of 30 attendees caught the virus. The six who were not infected were fully vaccinated.

Can children catch the Delta variant?

With the original COVID-19 virus strain, children were seen to be at lower risk than adults of contracting and transmitting the virus, however at least six children have contracted the virus in this outbreak, four at South Coogee Public School, one at Rose Bay Secondary College and one at Emanuel School, all in Sydney's Eastern Suburbs. Experts are now questioning whether the highly transmissible Delta variant spreads differently. Dr Chant describes the potential increased transmissibility among children as "a concern" and will "give us cause to strengthen our guidelines in relation to schools."


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