Delta symbols coming out of a red ball with spikes

The worst variant yet? Everything you need to know about Delta

The Delta variant of COVID-19 is now the dominant strain of the disease worldwide, and it has caused lockdowns in every mainland state and territory in Australia.

There’s still plenty to learn about Delta, but research is starting to trickle in, showing that in some ways it’s similar to the original (‘wild-type’) strain of SARS-CoV-2 that first emerged in 2019 – after all, it’s still SARS-CoV-2 – but in other ways it’s different. So, what do we know about the Delta variant?

How long have we known about Delta?

The Delta variant was first documented in India in October 2020. The World Health Organization didn’t list it as a ‘variant of interest’ (VOI) until 4 April 2021, and it wasn’t considered a ‘variant of concern’ (VOC) until 11 May 2021. (The definitions of VOIs and VOCs are detailed, but in short, a VOI is a widespread variant with genetic changes that may make it more virulent, and a VOC is a variant of interest that’s been shown to be more infectious or virulent.)

Prevalence of different COVID-19 strains over time, with the Delta variant shown in green. Source: nextstrain.org (CC BY 4.0)

So the vast majority of scientific research that focusses on Delta has only been going for a maximum four months. Consider what we knew, and didn’t know, about COVID-19 in May 2020, four months after it had been announced to the world.

Do vaccines work as effectively on Delta?

Preliminary data, such as this report on the Pfizer and AstraZeneca vaccines, shows that vaccines are still effective against the Delta variant. It’s difficult to compare efficacy between vaccines and variants, because every trial handles data and participants differently, but there is some evidence that the vaccines don’t work as well against Delta as they did against wild-type COVID, particularly if the person is only partially vaccinated.

As with wild-type COVID-19, vaccines are not 100% effective against Delta – there are confirmed reports of fully vaccinated people contracting and transmitting it. But vaccination still makes you much less likely to contract Delta, and even if you do, vaccines make you much less likely to experience symptoms.

Do masks work as effectively on Delta?

There isn’t yet much data on mask efficacy against Delta specifically – as with wild-type COVID, this is a difficult thing about which to gather data because there’s so much variation across regions, types of mask and mask use. But masks are likely to help slow the spread of Delta, and they certainly can’t hurt.

In the US, the  Centers for Disease Control and Prevention is recommending indoor mask usage among fully vaccinated people to reduce the spread of Delta. This represents a change in its policy – previously, fully vaccinated people weren’t thought to need masks.

Are children affected similarly by Delta?

There have been reports around the world of upticks in COVID outbreaks in schools, thanks to the Delta variant. But it should be noted that adult populations are increasingly becoming more vaccinated, while vaccines are still mostly not approved for children. Vaccine trials on children are starting to gather data – Moderna, which has recently been approved in Australia, has just ruled out Australian trials but is planning to test its vaccine in children as young as six months. The Pfizer vaccine has been approved for ages 12 and over in Australia.

Children and young people still mostly experience a very mild illness when they contract the Delta strain of COVID-19.

Are the symptoms the same as wild-type COVID-19?

There are some different symptoms associated with Delta. Headaches, persistent coughs, sore throats, runny noses, fevers and high temperatures are more common with Delta. Fever and loss of taste and smell were the most common symptoms associated with wild-type COVID.

As with wild-type COVID, symptoms can be very mild or very severe, so it’s important to get a test whenever you’re unsure.

There’s some evidence that Delta is more deadly, but more data is needed before we know for sure.

How infectious is it?

The Delta variant is more than twice as infectious as previous strains of SARS-CoV-2. There has been transmission of the virus during much shorter periods of contact than had been previously recorded.

It’s believed that the reason for Delta’s infectiousness is because it replicates more in the human body, creating a higher viral load.