Manuela Callari
The new highly infectious variant of SARS-CoV-2 first identified in the United Kingdom last December has landed in Australia. After a Brisbane quarantine hotel cleaner tested positive for COVID-19 on Wednesday, genomic sequencing confirmed that she was carrying the more contagious variant known as 501Y.V1.
How this new variant affects people who are infected is still unclear.
“It does not appear to increase disease severity or mortality,” says S S Vasan, CSIRO’s COVID-19 project leader. But a recent study, currently under review, suggests that it may be 56% more transmissible than previous variants.
That SARS-CoV-2 mutates into potentially more dangerous strains isn’t a surprise. All viruses mutate, and this coronavirus is no exception. “It’s very natural and very expected,” confirms Vasan.
Unlike other pathogens such as parasites, bacteria and fungi, viruses cannot reproduce on their own. To replicate, they must deliver their genetic code into the cells of the host they infect. Being such freeloaders means they will not be picky about their hosts and work with whatever cellular machinery they find. That often leads to many genetic mistakes.
“Thousands of mutations have been reported, and most of those mutations are harmless,” says Vasan.
But now and then, by sheer chance, a mutation can confer a slight advantage to the virus, such as in the 501Y variants detected in the UK (501Y.V1), and in South Africa (501Y.V2) last month.
These two strains carry a common mutation in position 501 of their genetic code. This mutation causes an alteration of the spike – the protein on the virus surface that vaccines target – enhancing receptor binding affinity and making the virus more transmissible.
That’s not surprising, says Vasan. Because only around 10% of the world’s population has been exposed to SARS-CoV-2 so far, the virus has plenty of hosts available. “It’s a natural selection process,” he says: the variants that are better at jumping from one person to another have an advantage in spreading their genetic code.
The emergence of new, more transmissible strains of SARS-CoV-2 has aroused widespread concern about whether the current vaccines being rolled out worldwide will remain effective.
A few months after SARS-CoV-2 was identified in China last January, a new variant called D614G, rapidly became the dominant lineage in Europe, the United States, Canada, South America and Australia. But animal studies and computer modelling show that the immune system can still neutralise the D614G strain, which means the current vaccines can protect against it.
This may also be the case for the 501Y.V2 strains.
“Based on what we know, it is not likely that these mutations are going to pose any problem to the efficacy of the vaccine,” says Vasan. But he warns that we can expect more mutations to appear as the population get vaccinated against the virus.
The more people are protected against SARS-CoV-2, the fewer people are available to host the virus to replicate. In a natural selection process, the virus could mutate to cause less severe but more protracted disease. That allows the virus to linger within one host until it finds the next available host to infect.
Vasan reassures that this is no reason for alarm. But he says it is crucial to monitor how the virus changes to ensure new mutations don’t impact vaccines’ efficacy.
On Thursday, the Federal Government announced that Australia’s Therapeutic Goods Administration is expected to approve the Pfizer/BioNTech vaccine by the end of January and vaccinations will begin in February instead of March as planned.
“We can speed up logistics in parallel so rollout can follow approval as soon as practicable,” suggests Vasan. In the meantime, “wearing masks, following social distancing and hand hygiene remains the best defence against new variants,” he says.
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