Since the COVID-19 pandemic began, the media has been quick to report on ‘worrying’ variants and speculate what they could mean for our road map out of lockdown and return to normality.
What they often fail to mention amongst the scaremongering is that viruses naturally mutate over time — and SARS-CoV-2, the virus that causes COVID-19, is no exception.
New variants often emerge and disappear. Other times, new variants emerge and persist. For this reason, scientists have been working behind the scenes since the early stages of the pandemic to monitor and study changes in the virus.
Through genetic analyses, scientists can learn more about how easily these variants spread, whether they could cause more severe illness and, crucially, whether current vaccines will protect people against them. For example, genetic sequencing first detected the emergence of the South East England variant, which has since become the dominant variant in the UK, and variants first seen in South Africa, Brazil and Japan.
Many more variants are likely to be identified in the coming months. So, let us take a closer look at how virus mutations work and practical advice for staying safe…
Mutations, variants and strains
Before looking at how viruses work, it is first worth considering the difference between mutations, variants and strains. Although the terms are often used interchangeably, they hold different meanings.
To spread, a virus needs to infect a host, replicate and produce copies of itself. However, when a virus replicates, it does not always manage to create an exact copy of itself.
Hosts can protect themselves from a virus by developing antibodies, which lock onto the outer surface proteins of a virus and prevent it from entering host cells. But if a virus appears different from other viruses that have infected the host, it has an advantage: the host has no pre-existing immunity.
As a result, the virus may start to change over time, adapting its genetic sequence. These changes are known as ‘mutations’, and viruses with new mutations are called ‘variants’. Variants can differ by one or multiple mutations. When a new variant has different functional properties to the original virus and becomes established in a population, it is sometimes referred to as a new ‘strain’ of the virus. It is worth noting that all strains are variants, but not all variants are strains.
DNA or RNA?
To understand how viruses mutate, it is also important to look at which type of virus it is. Viruses consist of hundreds or thousands of different atoms joined together, which make up the code of the virus’ DNA, or RNA (ribonucleic acid) in some viruses.
DNA is a more stable molecule than RNA, and DNA viruses have a ‘proofreading’ check as part of their reproductive process. If the virus makes a mistake in copying the DNA, the host cell can often correct the mistake. As such, DNA viruses do not change or mutate much.
RNA, on the other hand, is an unstable molecule. RNA viruses do not have this ‘proofreading’ functionality, which means mistakes frequently occur when copying RNA. Mutations are, therefore, common with RNA viruses.
In the context of the pandemic, this differentiation is significant. As with the human immunodeficiency virus (HIV, the virus that causes AIDS) and influenza viruses, coronaviruses’ genetic material is encoded in RNA. This is why we have seen — and continue to see — so many variants of coronavirus.
Most mutations are not a cause for concern. However, every so often, a virus mutates in a way that benefits it (for example, by allowing it to spread more quickly) and raises alarm bells.
For instance, VOC-20DEC-01 — the variant first identified in the UK — includes multiple mutations in the spike protein, including N501Y. (The spike protein is the outer part of the virus that first attaches to a human cell.) These changes have allowed the virus to become more infectious.
The variant first identified in South Africa (VOC-20DEC-02) shares the N501Y mutation to the spike protein but also has several other mutations, including E484K. Laboratory tests have shown that the E484K mutation may reduce antibody neutralisation.
As long as the coronavirus spreads through the population, mutations will continue to happen. In addition, there is new evidence that some immune responses driven by current vaccines could be less effective against some of the new strains. Given the recent rollout of vaccination programmes worldwide, this is — understandably — a concern for many.
However, the immune response involves many components, and a reduction in one does not mean the vaccines will not offer protection. It is also very unusual for any variant virus to render a vaccine completely ineffective.
It is also worth noting that the flu virus constantly mutates, too, which is why it is recommended to get a new flu vaccine every year. Scientists are continuing to research the effect of the coronavirus variants on vaccine efficacy. If required, this research will allow them to redesign and tweak future vaccines to be a better match against these variants — as is the case with seasonal flu vaccines.
Human behaviour and public health measures also play a part here. Even with the vaccine rollout, we must continue to be vigilant. The more people who are infected, the more chances there are for a concerning mutation to occur. As a result, it is crucial to limit the spread of the virus through social distancing, practising good hand hygiene and wearing an effective face mask solution.