What We Now Know About the SARS-CoV-2 Delta Variant That’s Wreaking Havoc Globally

“It is almost impossible to predict which variant will win the race and when we will have reached the point of most transferable,” said Dr. DiGiallonardo.

The Delta variant is likely to become the most dominant species worldwide. What does that mean for current and future variants?

Natural selection has shaped the evolution of all living things on our planet, including viruses. While mutations do occur in viruses, some mutations have little impact, while others outnumber and persist other variants, such as the SARS-CoV-2 variant, Delta – classified as a variant of concern (VOC) by the World Health Organization (WHO).

Last week, Dr. Poonam Khetrapal Singh, WHO’s Regional Director, Southeast Asia, said: “The Delta variant has spread to more than a hundred countries and is likely to become the most dominant COVID-19 strain worldwide soon. Of the worrying variants, Delta is spreading the fastest.”

Researchers have indicated that the Delta variant is the most transmissible variant to date – a whopping 60 percent more contagious than the Alpha variant. However, there is limited research on whether the Delta variant causes more serious illness than other variants.

The WHO characterization of variants was established at the end of 2020 as a result of variants with an increased risk to public health. These definitions help prioritize global monitoring, research and ultimately inform the ongoing response to the COVID-19 pandemic.

The R0 (reproduction number) of SARS-CoV-2 variants and other diseases. The higher the R0 number, the more contagious the disease is. Credit: Imperial College London, Lancet, Australian Government.

What is a care variant?

Currently, the Delta variant joins three other variants in this category: Alpha, which was first detected in the UK in September 2020; Beta, the earliest documented sample recorded in South Africa in May 2020; and Gamma, whose samples were first documented in Brazil in November 2020.

To be classified as a VOC, a variant must meet the definition of an interesting variant (VOI).

This includes a variant:

with genetic changes predicted or known to affect viral characteristics, such as transmissibility, disease severity, immune system escape, diagnostic or therapeutic escape; AND found to cause significant community transmission or multiple COVID-19 clusters, in multiple countries with increasing relative prevalence in addition to increasing number of cases over time, or other clear epidemiological effects indicating an emerging risk to global public health .

Currently designated variants include Eta, Iota, Kappa and Lambda.

To be “promoted” to a VOC, the variant must be associated with one or more of the following changes with some degree of global public health significance:

Increase in transmissibility or adverse change in COVID-19 epidemiology; OR Increase in virulence or change in clinical disease presentation; OR Reducing the effectiveness of public health and social measures or available diagnostics, vaccines, therapies.

Will Delta outperform the other variants of care?

As the Delta variant continues to spread globally, where does it leave other variants of concern, such as Alpha, Beta, and Gamma? Will Delta eventually outdo the others?

dr. Francesca Di Giallonardo, a virologist at UNSW Sydney’s Kirby Institute, suggests that may be the case.

“Most likely yes, as this is a common process in natural selection and immune escape. However, the timeline and characteristics of variant replacement may vary between different geographic regions, particularly in those isolated by border closures.

“Predicting the infectivity of new variants is not trivial. In general, viruses increase their portability. This means that the variant with the most ‘successful transmission’ outperforms the other variants. However, it is almost impossible to predict which variant will win the race and when we will have reached the point of most transferable,” said Dr. DiGiallonardo.

According to Dr. Di Giellonardo, increased viral fitness is characterized by natural selection events. This means that if variant B has replaced variant A, it must by definition be fitter, because BA has competed. Most likely, variant B is antigenically different, meaning it has escaped immune pressure.

“Such variants will continue to appear as immune selection is increased as more people are vaccinated or infected,” said Dr. DiGiallonardo.

Do fitter varieties cause serious illness?

If one variant outperforms other variants, does that suggest it could cause more serious disease in humans, or isn’t it? dr. Di Giellonardo said this assumption was not necessarily correct.

“New variants are so fitter that their replication and transmission capacity is better compared to the previous variants. There are numerous emerging variants that are region specific and do not seem to cause more serious disease.

“However, constant monitoring of such variants is crucial for identifying those that do indeed cause more severe disease. For example, the WHO and CDC (Centres for Disease Control and Prevention) classify new emerging variants with a potential for increased severity as worrisome and interesting variants.”

What is our best line of defense?

“Vaccinate, vaccinate and vaccinate,” said Dr. DiGiallonardo. “We have an abundance of global data on the efficacy of the various vaccines. We know how effective they are in preventing serious diseases and reducing transmission.”

Virologist, Dr. Chantelle Ahlenstiel of the Kirby Institute said that in terms of the mRNA vaccines like Pfizer and Moderna, the sequences in current vaccines — which tell the body how to make a specific type of virus spike protein — can easily be changed to corresponds to the newly emerging spike protein of the virus variant and can therefore also offer protection against it. In addition, mRNA vaccines have the potential to be manufactured quickly and inexpensively.

Surveillance is also critical to understand which variants are circulating, as early identification will allow rapid evaluation of vaccine efficacy.

“Surveillance means collecting data on the number of infections present for different virus variants, their geographic distribution and the associated disease severity. Such data is essential to better understand how variants spread across states, countries and globally. We have more data for Covid-19 than for any other viral disease, thanks to systems that were already in place, such as nexstrain.org, GISAID (Global Initiative on Sharing Avian Influenza Data),” said Dr. DiGiallonardo.

“Surveillance requires a tremendous amount of work and the global effort has been great.”