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The source of concern
A virus continually undergoes mutations. The more the number of infected people increases, the more the risk increases that one of these mutations will make this virus more “effective”. Since the start of the pandemic, one of the main fears has therefore been to see a more contagious variant appear.
According to the first research, the variant first detected in the UK in November, and which had been circulating since at least September, appears from 50 to 74% more transmissible than other versions virus. Researchers attribute it to a mutation, similar to that spotted in the variants that appeared in South Africa and Brazil, and which allows the virus to bind better to our cells.
In a preliminary (and not yet peer-reviewed) analysis published on January 15, British researchers reportedly observed greater viral load in people infected with the variant, which would explain why they are more contagious.
However, there is no indication that people infected with these new variants are sicker than others or have different symptoms. And there is also no indication that the death rate is higher, which was immediately seen as reassuring news.
More cases: more deaths
But the news is not reassuring for all that. Because it’s a matter of statistics: a more contagious virus that spreads more in the community means that sooner or later there will be more hospitalizations. In other words, the more people are infected, the more people are hospitalized and the more likely there is to be death. And this, even if the virus is not more deadly.
“A virus which is 50% more contagious is even more worrying than a virus which is 50% more deadly”, summed up on Twitter the British epidemiologist Adam Kucharski.
The way to assess this is through the concept of the virus’ reproduction rate, or R. When R is 1, each infected person transmits the virus, on average, to another person. The number of cases thus remains the same, from week to week. The objective of the various measures (confinement, distancing, mask, etc.) is therefore to bring this figure below 1.
For example, in Quebec this fall, this rate fluctuated between 0.92 and 1.18. An increase in transmissibility of 50% could therefore mean an R of around 1.5. If it were to reach this threshold, it would be a rate comparable to that which had been reached at the end of March, when we were approaching the peak of the first wave.
The magazine Vox illustrated Adam Kucharski’s claim by a fictitious community where 10,000 people are infected. Suppose that each person infected an average of 1.1, before the arrival of the new variant. Considering that it can pass a few days between the moment when a person is infected and when it is contagious, a month later (in the 5th “generation”), 16,000 were infected. Assuming a death rate of 0.8%, as was the case in England at the end of the first wave, the death toll would be 128.
Now imagine two scenarios. In the first, the virus becomes 50% more deadly: there would be 192 dead rather than 128, after a month. In the second scenario, it “simply” becomes 50% more contagious, as seems to be the case with this new variant: the number of cases then reaches 122,000 after one month, which would represent 978 deaths.
A british study unpaired review, released Jan. 4, concluded that the variant in question was spreading with a rate of 1.45 – despite health restrictions – compared to the old version’s spread rate of 0.95. A week earlier, a preliminary analysis of Imperial College London was even more disturbing, citing different estimates that placed the reproduction rate between 1.4 and 1.8.
We can qualify this by recalling that deaths occur more in vulnerable populations, and that it is not inevitable that this variant penetrates environments where reside populations that are sicker or older.
But we can also add that if the contagion rate is higher, the percentage of the population that will have to be vaccinated to achieve collective immunity will also have to be higher.
Verdict
A more contagious virus inevitably leads to an increase in hospitalizations, and these carry an increased risk of an increase in deaths, at least as soon as the virus reaches the most vulnerable populations.
Infographic: Steve Proulx
Photo: Gerd Altmann / Pixabay
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