Understanding the Delta variant – Expert Reaction

Health officials are assuming the Sydney man who visited Wellington over the weekend has the Delta variant of the COVID-19 virus.

Australian authorities expect his case to be genomically linked to the current Sydney outbreak, where the Delta variant (B.1.617.2) is spreading. Results from genomic sequencing are expected today.

The SMC asked experts to comment on what we know so far about this variant.

Dr Jemma Geoghegan, Senior Lecturer, University of Otago, comments:

“The Delta variant is a variant of concern because data from the UK suggests that it could be up to 60 per cent more transmissible than the already highly transmissible Alpha variant. Because of the very good genomic sequencing effort by the COVID-19 Genomics UK Consortium, they have very good data on these emerging variants. Their data also suggest that people infected with the Delta variant have an increased risk of hospitalisation, and that two doses of either the AstraZeneca or Pfizer vaccine is far better than just a single dose at reducing the risk of developing symptoms.

“It might be the case that someone infected with the Delta variant doesn’t transmit to anyone, as we have shown previously that only around 20 per cent of people infected in New Zealand during the first wave actually went on to infect someone else.”

No conflicts of interest

Dr Michael Maze, Senior Lecturer, Department of Medicine, University of Otago, Christchurch, comments:

“The SARS-CoV-2 Delta variant has taken off worldwide because it is more transmissible than previous strains of the virus. In terms of the illness it causes, it causes a wide range of possible symptoms. Data from the UK suggests that many people there get what looks like a cold – with headache, runny nose and a sore throat very common. Some of the symptoms that got a lot of airtime last year – such as loss of smell – seem less common.

“The bottom line is that it is very hard to reliably tell whether ‘cold’ type symptoms are due to COVID-19 and people who get a fever, runny nose, cough, sore throat or headache should get tested for COVID-19.

“Like previous variants most people with the Delta variant will not get severely unwell. We don’t yet know if this variant causes more or less severe disease than previous variants. Early reports suggested that it was more severe with people infected with the Delta variant up to twice as likely to be admitted to hospital. Conversely, in the UK there has been a suggestion that it might be less severe – but this is probably due to the fact that the disease is spreading among younger people.

“Older people who have received two doses of vaccine seem to be well protected – and it is these people who would have been at the highest risk of life-threatening illness. It is likely that the overall range of severity will be fairly similar to previous variants, with many people having mild symptoms and a minority will end up with a life-threatening illness. Again, vaccination is the best defence we have, and it serves as a reminder of the need for all of us to get vaccinated when possible.”

No conflict of interest

Professor Michael Plank, Te Pūnaha Matatini and University of Canterbury, comments:

“The Delta variant is around twice as infectious as the strain we dealt with last year. We know this from UK data showing that people with Delta consistently pass the virus on to a higher proportion of their contacts than people with the Alpha variant do. We have also seen cases in Sydney where the virus has spread after very fleeting contact, showing it is possible to catch it simply from sharing the same airspace as an infected person.

“That makes this variant extremely dangerous because of the way cases can grow exponentially. For example, after just three chains of transmission, there would be eight times as many cases on average. So, where the original variant might have caused 10 cases, the Delta variant could cause 80 cases in the same time, which would quickly make it impossible to control without a lockdown.

“The Delta variant also appears to carry approximately double the risk of hospitalisation as the Alpha variant. There is insufficient data at present to compare the fatality rate of Delta with other variants.

“The good news is that vaccines still work for the Delta variant. Data from the UK show that the Pfizer vaccine being used in New Zealand is highly effective against symptomatic disease, hospitalisation and death caused by Delta after two doses. However, the effectiveness after only one dose is much lower, so it will be really important to make sure everyone gets that second dose when their turn comes.

“The measures that we know work in controlling COVID-19 in general (e.g., testing, contact tracing, masks, reduction in indoor gatherings and crowds) also work for Delta. But because it’s more transmissible, we may need more of these, or we may need to use them for a longer time than previously. Right now, vaccination coverage is too low to make much of difference in controlling any outbreak. So, we need to take the threat of this variant very seriously, and take the measures needed to stamp it out as quickly as possible.”

Conflict of interest statement: “I am partly funded by MBIE for research on mathematical modelling of COVID-19.”

Lesley Gray, Senior Lecturer, Department of Primary Health Care & General Practice, University of Otago, comments:

“Readers may recall when we first learnt of the so-called ‘Kent’ variant (Alpha) originating in England.  This was seen as a much more transmissible variant than the original virus.  In comparison, the Delta variant (believed to have originated in India) is more than 60 per cent more transmissible than that Kent variant indoors. So, it is a very fast transmitter, and this is cause for concern.”

Conflict of interest statement: “Lesley Gray is a named researcher on several Health Research Council grants relating to COVID-19.”

Associate Professor Arindam Basu, Associate Professor of Epidemiology and Health Sciences, University of Canterbury, comments:

“According to GISAID, the Delta variant is rapidly becoming the dominant variant internationally and pretty much has spread across the world. It first started its life in India as a mutant back in April-May and according to Public Health England, the attack rate is about 50-67 per cent higher than the older variants (the “Alpha” variant), so that should tell us a story that it spreads fast. The scary part is that it has a tendency to spare no specific age groups.

“A new emergent variant is called Delta plus, and it has started spreading as well.”

No conflict of interest