Coronavirus variants and mutations: the science explained
Scientist with a model of the virus
The discovery of two variants of the coronavirus triggered an alarm.
Scientists are trying to figure out whether these variants are more transmissible or could pose challenges for the Covid vaccine.
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All viruses naturally mutate, and Sars-CoV-2 is no exception, producing an estimated one or two changes per month.
Mutations are usually a random event that has little effect on the properties of a virus, says Dr. Lucy van Dorp, an expert on pathogen evolution at University College London.
"The vast majority of the mutations we see in the Sars-CoV-2 genome are present as passengers," she says.
"They don't change the behavior of the virus, they just get carried away."
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But every now and then a virus gets lucky by mutating in ways that are beneficial to its ability to survive and reproduce.
"Viruses that carry these mutations can then occur more frequently due to natural selection based on the right epidemiological settings," says Dr. van Dorp.
There is now a hectic urge to find out if this is the case with the variant (B.1.1.7 or VUI-202012/01) first discovered in the UK, which seems to be spreading unusually quickly.
A similar, but unrelated, variant has occurred in South Africa and a small number of cases have now been reported in the UK.
Britain has found two cases of variant in South Africa
Of particular concern is the fact that both have mutations in a gene that codes for the spike protein that the virus uses to attach to and enter human cells.
The UK variant has 14 mutations that cause a change in the protein building blocks (amino acids) and three deletions (missing parts of the genetic code).
According to the World Health Organization (WHO), some can affect the spread of the virus.
A mutation in the spike protein (known as N501Y) has been detected in several variants, including that from South Africa. Laboratory experiments suggest that this mutation may help the virus bind to human cells, according to the Centers for Disease Control and Prevention (CDC).
Another mutation in the spike protein (P681H) is of "biological importance" according to the WHO
A deletion (at position 69-70) has been linked in the past to outbreaks of mink farming and in immunocompromised patients who can incubate the virus for several months
The deletion may provide some clues as to the development of the variant, possibly in a patient with a weakened immune system who was unable to fight off the virus, allowing it to stay in the body for several months and accumulate mutations.
"Currently, it is believed that so many mutations have developed related to chronic infection," says Prof. David Robertson of the University of Glasgow, part of the Cog UK (Covid-19 Genomics UK Consortium), the new one has analyzed variant.
Mink outbreaks are an "overflow" of the human pandemic
A connection with mink is considered highly unlikely. "There is no evidence that mink or other animals are involved, but it makes sense not to rule this out," says Prof. Robertson.
What is the science behind mink and coronavirus?
Scientists are now rushing to find out more about the mutations in the British variant, which was also discovered in Australia, Denmark, Italy, Iceland and the Netherlands.
The variant found in South Africa, which has one of the same mutations, is also worrying. It shares the same mutation in the spike protein (N501Y) but occurred separately. Other mutations are being investigated.
There is strong suspicion that both variants are spreading faster than expected, but this is still unclear.
Hundreds of thousands of viral genomes have been analyzed worldwide
Sars-CoV-2 has been at the center of an unprecedented international scientific effort since early January, when researchers in China published the first genome sequence.
Scientists have now sequenced over 250,000 Sars-CoV-2 genomes that have been shared on open data platforms.
By removing a swab from an infected patient, the genetic code of the virus can be extracted and amplified before it is "read" with a sequencer.
The sequence of letters or nucleotides enables genomes and mutations to be compared.
"Thanks to these efforts and the UK testing laboratories, the UK variant was quickly identified as a potential cause for concern," says Dr. van Dorp.
Scientific information is now being exchanged at an amazing rate.
An important question is whether the mutations could have any impact on vaccine effectiveness, although many experts believe this is unlikely, at least in the short term.
"With the introduction of vaccines, this is becoming increasingly important so that plausible candidates can be identified, followed up and pursued at an early stage," says Dr. van Dorp.
"In the longer term, we may need to reassess the composition of the vaccine and its delivery strategy, so these efforts are critical. But it's too early to say for now."
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