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

COVID Variant Illustration

“It’s almost impossible to predict which variant will win the race and when we have reached the point of most transmissible,” said Dr. Di Giallonardo.

The Delta variant is likely to become the most dominant strain globally. 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 emerge in viruses, some mutations have little impact while others outcompete other variants and persist, such as the SARS-CoV-2 variant, Delta – classified a variant of concern (VOC) by the World Health Organisation (WHO).

Last week, Dr. Poonam Khetrapal Singh, the regional director of the WHO, South-East Asia said, “The Delta variant has spread to over a hundred countries and is likely to soon become the most dominant COVID-19 strain globally. Among the variants of concern, Delta spreads most rapidly.”

Researchers have indicated the Delta variant is the most transmissible variant yet — as much as 60 percent more contagious than the Alpha variant. However, there is limited research in terms of whether or not the Delta variant causes more severe illness than other variants.

The characterization of variants by the WHO came about in late 2020 as a result of variants that posed an increased risk to public health. These definitions assist in prioritizing global monitoring, research, and ultimately informing the ongoing response to the COVID-19 pandemic.

Infectious Disease Reproduction Numbers

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 variant of concern?

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, which had samples first documented in Brazil in November 2020.

To be designated a VOC, a variant must meet the definition of a variant of interest (VOI).

This includes a variant:

  • with genetic changes that are predicted or known to affect virus characteristics such as transmissibility, disease severity, immune escape, diagnostic or therapeutic escape; AND 
  • identified to cause significant community transmission or multiple COVID-19 clusters, in multiple countries with increasing relative prevalence alongside increasing number of cases over time, or other apparent epidemiological impacts to suggest an emerging risk to global public health.  

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

To be ‘promoted’ to a VOC, the variant needs to have shown to be associated with one or more of the following changes at a degree of global public health significance: 

  • Increase in transmissibility or detrimental change in COVID-19 epidemiology; OR
  • Increase in virulence or change in clinical disease presentation; OR
  • Decrease in effectiveness of public health and social measures or available diagnostics, vaccines, therapeutics.  

Will Delta outcompete the other variants of concern?

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

Dr. Francesca Di Giallonardo, a virologist at The Kirby Institute at UNSW Sydney suggests this could potentially be the case.

“Most probably 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.  

“Prediction of infectivity of new variants is not trivial. In general, viruses increase their transmissibility. That means that the most ‘successful in transmission’ variant outcompetes other variants. However, it’s almost impossible to predict which variant will win the race and when we have reached the point of most transmissible,” said Dr. Di Giallonardo.

According to Dr. Di Giallonardo, increased viral fitness is characterized by natural selection events. This means if variant B has replaced variant A, it must be fitter by definition, as B has outcompeted A. Most likely, variant B is antigenically distinct, which means it has escaped immune pressure.

“Such variants will keep emerging as immune selection is increased due to more people being vaccinated or infected,” said Dr. Di Giallonardo.

Are fitter variants likely to cause severe disease?

If a variant outcompetes other variants, does that suggest it can cause more severe disease in humans or is that not the case? Dr. Di Giallonardo said this assumption was not necessarily correct.  

“New variants are fitter such that their replication and transmission capacity is better compared to the previous variants. There are numerous emerging variants that are region-specific and are seemingly not causing more severe disease.

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

What is our best line of defense? 

“Vaccinate, vaccinate, and vaccinate,” said Dr. Di Giallonardo. “We have a plethora of global data on the efficacy of the different vaccines. We know how effective they are in preventing severe disease and reducing transmission.”

Virologist, Dr. Chantelle Ahlenstiel at the Kirby Institute said in terms of the mRNA vaccines such as Pfizer and Moderna, the sequences in the current vaccines – that tell the body how to make a specific type of virus spike protein – can be easily changed to match the newly emerging virus variant spike protein and could therefore provide protection against those too. Additionally, mRNA vaccines have the potential to be manufactured rapidly and inexpensively.

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

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

“Surveillance requires a tremendous amount of work and the global efforts have been great.”

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

  1. Carolyn L Zaremba | August 4, 2021 at 2:26 pm | Reply

    Relying purely on vaccination, particularly in an environment where the vast majority of people are not vaccinated, is not enough. Isolation and social distancing must continue, along with mask-wearing, to assure that transmission is slowed. This has been proven to work, even before the vacciness were developed. As long as the virus continues to thrive in many third-world countries and in certain areas of the developed world, it will continue to mutate. The goal should be to prevent the longevity of the virus to eliminate its potential for further mutation. Vaccinate by all means, but as long as vaccine formulations are considered “intellectual property” by pharmaceutical companies, and as long as many countries do not have the health infrastructure to efficiently distribute and administer inoculation, these other non-pharmaceutical measure must continue and be enforced across the board.

  2. Has anyone, anywhere investigated a possible causal link between the Vaccination Program and the proliferation of COVID variants and, particularly, the current CoV Delta variant? The RO graphic contains a “suggestion” of said, inasmuch as it also indicates a significant upsurge in the number of cases, and the increasing severity and “apparent” increase in transmissibilty with each successive variant. This ancillary “phenomenon” seems coincident with firstly: the development and deployment of the first rRna vaccine and, secondly: the increase in the percentage of vaccinated individuals and populations. Also of concern is the growing number of vaccinated individuals who are experiencing CoV (re)infection and the attendant symtomology. There is a transmission VECTOR in there, SOMEWHERE, despite much touted (and “inconvenient”) prophylactic measures. To wit: if the vaccinated are not “safe” and the unvaccinated are not “safe”, what is “fueling” the variant chain AND the upsurge in infections. It begs yhe question: could the CURE be as bad (if not worse) than the CAUSE? 🤔

    I’m just sayin’.

    • This is the “gambler’s” fallacy applied to disease. If something is having babies every day, then there’s going to be a lot more mutations than humans or even rabbits, especially if it gets into a massive population like India where almost nobody is vaccinated.

    • Frosted Flake. | August 7, 2021 at 3:41 am | Reply

      “Has anyone, anywhere investigated a possible causal link between the Vaccination Program and the proliferation of COVID variants and, particularly, the current CoV Delta variant?”

      I doubt it. No one would thin to. It works the other way. The virus mutates frequntly and so will eventually find a way around the vaccine by brute force and massive ignorance. But this capability will be developed because the unvaccinated provide their bodies for the virus run wild. And one fine bright day we will be back at square one. Because republicans.

  3. @Alex: Just because you use phrases like “to wit” doesn’t mean you have any. The vaccinated ARE far, far safer than the unvaccinated – they sometimes get it, but they don’t die and they don’t get long covid. It’s a pity that someone such as you who clearly writes so well is providing anything but clarity to others. Perhaps you should just stop sayin,

  4. Howard Jeffrey Bender, Ph.D. | August 5, 2021 at 12:00 pm | Reply

    All the variants have different spike proteins, with Delta having one that is more efficient at getting around the vaccines. But the real problem is in the virus and why two of the most dangerous, MERS and Covid-19, are so infectious. My independent research has found multiple one-in-a-million nucleotide sequence matches between all the coronaviruses and the human genome. Those sequences are the same as some of the DHU loops of human tRNA. Using those loops and their anticodon matches, viruses may be able to fool the nucleus membrane in cells to allow the virus to enter and associate with the human DNA, creating more opportunities for further infection. Our immune system may be compromised and may no longer be able to stop the virus and other diseases from attacking organs throughout the body. Vaccines that attack the virus protein shells while ignoring their contents are doomed to failure from the Darwin effect, but recognizing these DHU loops suggests a possible approach to successful coronavirus vaccines. For MERS, eliminating the nucleotide sequence CAGTGGTAG from the virus may make it less infectious and stimulate the body to create antibodies to attack the entire virus. And eliminating the nucleotide sequence TAGTGGTGAG from Covid-19 may do the same thing. Only the infection process is considered in my work, not the innate virulence of the virus. For more info, check out this YouTube, Coronavirus – Using Your DNA Against You. https://www.youtube.com/watch?v=pd4OD4GpsJI

  5. Why the derisive shaming of Alex for asking a question? This kind of response (of the following two commenters) is destructive of human discourse, and really, of science. Much thanks to the longer, matter-of-fact, objective perspective of someone doing current research. Thanks, too, to someone brave enough to ask a question no one is – clearly – “supposed” to ask.

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