by Saurabh Mahajan
The past year has thrown into limelight a field of biology that is rarely on the public’s scientific and technological horizon. That field is evolution. Right in the early days of the pandemic, the question of “whether this virus will mutate to become more dangerous” had started making rounds. Unfortunately, we are now at that stage. But the story is much more complicated than this simple question. Thanks to the extraordinary efforts of researchers around the world, we can detect and study viral mutations within a matter of days. So what do we know on this front so far?
Detection and origin of SARS-CoV-2 variants
In January 2020, within days of detecting the first cases of an infectious respiratory disease, the RNA sequence of the causative virus was deciphered and made publicly available. Thereafter, sequencing the viral RNA became routine. Sequencing virus samples at regular intervals, comparing them to the sequences of previous samples, and using computational methods to infer their progressing evolution has allowed researchers to detect and track thousands (yes) of variants of the virus. This is not because SARS-CoV-2 is exceptional at mutating. Rather we know that mutations in SARS-CoV-2 happen relatively less frequently than other respiratory viruses such as Influenza. However, the virus in each new chain of infection keeps accumulating mutations independently. Thus, as the pandemic has expanded to millions, so have the number of virus variants to thousands.
Major concerns about variants
There are at least three major concerns regarding mutations in any virus: do the mutations make it more infectious; do they make it more severe or lethal; and do they cause it to escape and resist our natural or vaccine-induced immunity. The increase in infectivity implies that the virus will spread faster and will be harder to control. Increased severity and lethality means more deaths and a healthcare burden. And escape from the immune system implies that the virus could potentially cause reinfections and make current vaccines less effective. Compared to the virus that was first identified from Wuhan, we are now seeing multiple variants that are either more infectious, or more lethal, or which can escape immunity, and a combination of these characters.
Evolution of some major variants
Multiple variants of the virus called 501Y.V1 (B1.1.7), 501Y.V2 (B1.1.351), and 501Y.V3 (B1.1.248) that arose in the UK, South Africa, and Brazil respectively have caused concern. They all carry different combinations of mutations but also share one unique mutation in the spike protein- a replacement of amino acid N at position 501 by amino acid Y. Within three months, the 501Y.V1 variant has almost completely replaced other existing variants in England. From its rate of expansion, it was figured out that it was at least 50% more contagious, and multiple studies are showing that it is perhaps 30% more lethal. The 501Y.V2 and V3 variants have other shared mutations such as the E484K and are greater causes of worry. The 501Y.V2 variant that arose in South Africa is also similarly more contagious.
Additionally, preliminary reports had indicated that the plasma from several already infected or vaccinated patients (who must have multiple antibodies against the virus) could be less efficient at neutralizing this variant. Now, data from a small trial in South Africa is showing that the Oxford-AstraZeneca vaccine is not very effective at controlling 501Y.V2. This has led South Africa to pause the rollout of this vaccine! The 501Y.V3 variant may also be a greater cause of worry for the possibility of causing reinfections. It was found in a region of Brazil that experienced a large pandemic spread during the first wave and yet, is experiencing a strong second wave after many months. This could be due to greater chances of reinfection by this variant, but this still needs to be thoroughly studied.
Relevance for India
Fortunately, in India, we are on a downward trajectory in the number of cases, hospitalizations, and deaths. This is most likely because a large fraction of the population (>40%), at least in our major cities, has already been infected and is thus probably immune. Even if this is true, two things can pose a renewed threat. One is waning immunity. The second is the evolution of viral variants that can cause reinfections in already immune persons. Thankfully, we have heard no news concerning variants arising in India so far. However, variants arising in other places can quickly travel around, e.g. the B1.1.7 variant that arose in the UK traveled to many other countries and is on the rise.
We also need to be mindful that the slow pace of any exponential growth in early phases can deceive us for a long time. Thus, tracking emerging variants of the virus is paramount. Thankfully, the Indian government has already made progress in this direction by establishing a consortium to sequence 5% of all viral samples. Indian laboratories are also keeping a watch on the variants from India and possibilities of escape from the immune system.
Evolution in focus
While we fight this pandemic and emerge from it, it may be worth remembering that evolution is not an archaic field of biology. Even when we are not paying attention, all organisms including ourselves are evolving, albeit at different speeds. And some of the same fundamental processes that cause a virus to evolve, are also responsible for the evolution of the good, the bad, and the ugly on our planet. Apart from SARS-CoV-2 and bacteria resistant to antibiotics, evolution has also given us all our amazing biodiversity and many useful organisms such as crops and pets. If we want to cherish the biodiversity on our planet and keep our species safe and productive, it is imperative to appreciate and understand evolution more and support research in evolutionary biology.
DISCLAIMER: The views expressed are solely of the author and ETHealthworld.com does not necessarily subscribe to it. ETHealthworld.com shall not be responsible for any damage caused to any person/organisation directly or indirectly.
[The writer is Assistant Professor of Basic Sciences at Atria University, Bengaluru, and a researcher of microbial evolution.]