- A study has found that the coronavirus strains aren't very diverse
- This means that one vaccine would be able to offer universal protection against SARS-CoV-2
- The D614G strain appears to be the most dominant in 84 countries.
As the world rushes to produce a vaccine to fight off the coronavirus, questions have been raised over whether one vaccine would be able to counter all the different strains of the virus.
After all, what would be the point of a vaccine if it only offered protection against certain strains?
A mammoth study published in PNAS sought to answer this question by ascertaining how many different strains of the virus might be currently circulating in the world.
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Samples from 84 countries
The researchers analysed 18 514 SARS-CoV-2 sequences sampled from infected individuals in 84 countries since December 2019, and compared them to 30 strains sampled at the start of the outbreak in Wuhan and the strains being used to develop vaccines in various trials.
They found that the virus genomes weren't incredibly diverse, with only 5% of sequences showing 11 types of mutations and two mutations dominating the coronavirus population.
Wuhan-Hu-1 was the first strain to be derived at the start of the pandemic and is likely to form the basis for most of the vaccines being trialled. Newer strains don't differ too much from this original one and are only one mutation away from the current most dominant strain, D614G.
"Because SARS-CoV-2 is being transmitted more rapidly than it evolves, the viral population is becoming more homogeneous, with a median of seven nucleotide substitutions between genomes," write the researchers.
Neutral vs. adaptive evolution
A virus becomes fitter with every mutation, and while there might be more mutations to come, their frequency will decrease over time.
The reason for this is that SARS-CoV-2 is following a neutral evolution path as opposed to an adaptive evolution path.
The former means that the variation between strains are more random, while the latter is more Darwinian in nature. The best and strongest genes are passed on while the weaker ones are left behind.
Any sequence can be used
Before travel restrictions kicked in during March this year, many variants made their way through China, Europe and the US. However, at the genome level, these variants don't differ that much at all.
"A randomly selected SARS-CoV-2 sequence could be used as a vaccine candidate, given the similarity of any sequence to the computationally derived optimum vaccine candidate.
"Vaccines developed using any of these sequences should, theoretically, be effective against all circulating viruses. Vaccine developers could consider designing a vaccine insert with the D614G mutation in S, as this mutation has become dominant worldwide.
This is not to say that there won't ever be drastic mutations, just that they will be rare. It's important to note that the virus is still relatively "young" in humans – and it is unknown how it will mutate in years to come.
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