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One of the new worrisome viral genetic variants is the « UK variant » (lineage B.1.1.7.). Around the world, this variant has triggered a wide range of attention from public health officials, scientists and governments. This is particularly true in Quebec where the UK variant is the most common variant.
Within this context, is the UK variant complicating our efforts to end this pandemic?
To answer this question, we have to consider what we know about the variant so far.
Viruses evolve all the time
Although a new form of the virus may seem scary and abnormal, this is nothing unusual. For instance, flu shots are annually updated to deal with its new strains. Changing is what viruses do.
The Severe acute respiratory syndrome coronavirus 2 (SARS-Cov-2), in cause for COVID-19, is no exception. It tricks infected cells of human (and some animals) into producing more copies of itself. To replicate the virus, an infected cell has to recopy without errors the RNA sequence of the virus. This sequence of about 30,000 letters long encodes instructions to make the virus.
An infected cell can produce up to 1,000 new virus particles. This is around 30 million of opportunities to make mistakes, and this is only for one cell (one individual is composed of billions of cells).
Those mistakes are called mutations. Most of the time, mutation will occur without altering the virus or by disabling its ability to replicate. On some occasions, the genetic sequence of the virus will change much that we will call it a variant.
Fortunately, SARS-Cov-2 mutates at least twice as slowly as the influenza virus. First, it has a proofreading mechanism that can correct errors in the replication of his genetic sequence. Second, SARS-Cov-2 rearranges less efficiently than other RNA viruses.
Briefly, the influenza virus has 8 segments of RNA that can reorganize themselves - a process called reassortment - by swapping their segments for those of another influenza virus inside an infected cell. This process can cause rapid changes in the function of the virus.
On the contrary, SARS-Cov-2 does not have a physical segmentation of its RNA, rendering it incapable of reassortment. It can experience some shift in function through a process called recombination, when the enzyme recopying its genetic sequence blend parts together. In viruses, this process is generally less efficient than genetic reassortment for evolving.
So far, the virus generally accumulates one or two mutations per month that do not change its properties.
However, the more people the virus infects, the more likely it is to accumulate mutations and change. The heavy circulation of SARS-Cov-2 in the world has given to the virus considerable opportunities to evolve, which has led to the emergence of variants, including the UK variant.
The UK variant is distinctive as it acquired 23 mutations in his genetic code, marking a distinct shift from the original virus.
The spike proteins are intriguing
Spike proteins are like hooks on the surface of the virus. It allows the virus to bind and latch onto a cell. Consequently, too many changes in the spike protein would jeopardize the survival of the virus by preventing it to infect the cells that are key to its life cycle.
The UK variant found a combination of mutations favorable to its survival. In particular, it has several mutations in the spike protein, making it more efficient at binding to cells (more transmissible) and at bypassing the immune system.
It is not the only one. Since the start of the pandemic, many more transmissible variants have been detected, including several with similar mutations. For instance, three variants present in Quebec (British, South African and Brazilian) have the N501Y mutation where a letter has been modified in the RNA sequence corresponding to the spike protein.
The appearance of similar mutations at different times and places supports a convergent evolution of the virus. For example, dolphins and sharks both acquired a dorsal fin while having evolved independently.
Similarly, SARS-Cov-2 may seek to adapt its genetic sequence in order to maximize its survival, but its options would be limited. It's a bit like a game of tetris where the goal is to assembly blocks together, but the pieces are not always optimal. There are only a few winning combinations which all have similar characteristics.
The fact that scientists are observing the same mutations occur in different variants would support that the virus is running out of options to reinvent itself without compromising its fitness.
For several experts, this phenomenon is encouraging.
In Canada, the four authorized COVID-19 vaccines are based on the spike protein to generate immunity. Too much variation would make vaccines ineffective, but this is unlikely to happen.
As seen with the UK variant, the virus may have limited ways to increase its chances of survival. In addition, vaccines produce a large array of antibodies against different parts of the spike protein. Therefore, it would be very unlikely that the spike protein would change enough for the vaccines to be completely ineffective.
To date, there is convincing evidence that all four vaccines protect against hospitalizations and death from infection of the UK variant. In Scotland, where the UK variant accounts for the majority of new infections, AstraZeneca and Pfizer/BioNTech vaccines have reduced the number of hospitalizations after a single dose by 74% to 90%. These results have been corroborated elsewhere in the world.
However, nature is unpredictable. The virus will keep searching ways to nail infection among human as long as the virus circulate.
This is why in Quebec, as elsewhere in the world, the UK variant only reinforces the importance to contain new infections.
The UK variant quickly settled and spread in Quebec
The variant was first detected in the United Kingdom last September. Across the ocean, the first case in Quebec was confirmed in late December. By the end of March, it was dominant in the province, meaning the majority of new infections were attributable to the UK variant.
The rise of the UK variant came at a time when health measures were relaxed by the Quebec government. Within this context, the increase in infections and hospitalizations, especially among young adults, may reflect a higher transmissibility of the UK variant and its rapid spread in the community.
The predominance of the UK variant is of concern, as its greater ability to transmit and infect also means more opportunities to mutate. However, one has to remember that transmission mainly depends on how individuals protect themselves through social distancing and wearing a mask.
So far, wearing mask and physical distancing have been shown to be very effective in reducing person-to-person transmission. Moreover, until a massive rollout of vaccination around world, several effective public health measures can be prioritized to reduce the impact of COVID-19.
To conclude, the path to defeat the pandemic remains the same despite the UK variant.