About two months after Omicron’s discovery, we have enough data to argue that it is a less lethal variant of Delta. The very first data on hospitalizations in South Africa were confirmed both by English data and by in vitro evidence collected in the laboratory.
Despite the numerous mutations and the ability to evade (at least partially) the immune response in vaccinated and cured subjects, the Omicron variant appears to cause about a third of hospitalizations caused by Delta.
This difference can be partially explained by the presence of vaccines. In fact, in England most of the population is vaccinated and / or cured and, although the Omicron variant avoids neutralizing antibodies, we know that vaccines remain effective even after months in avoiding the contraction of severe disease, hospitalization and death.
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Biologically less severe
The numerous mutations that characterize Omicron have made it extremely more contagious, so much so that, according to some estimates, the Omicron variant would be the most contagious virus that has ever existed on earth. At the same time, this wide range of mutations helped to modify the biology of this variant, making it less aggressive.
One of the most impressive and dangerous features of the previous variants was the ability to form pulmonary syncytia: syncytia are formed when two or more cells merge into a single cell. The formation of syncytia in the lung damages the function of the respiratory system and is thought to be induced by Sars-CoV2 to ‘escape’ the immune system.
In the Omicron variant, on the other hand, far fewer pulmonary syncytia are observed, which suggests two things: firstly Omicron develops less deeply (in fact it does not always reach the lungs) and, secondly, it is less efficient in creating these deleterious syncytia.
Why will Omicron never get a cold despite being less severe?
Recently we have often heard the expression “the virus is getting cold”: why is this expression incorrect and dangerous?
With the generic term of cold we describe a series of symptoms that typically occur in the winter season: cough, sneezing, runny nose, headache etc.
These symptoms are triggered by a series of viruses including coronaviruses (same family as Sars-CoV2), although the main culprit is the rhinovirus.
Let’s take a look at the cold caused by the rhinovirus and see if we can compare it to Sars-Cov2. Rhinovirus causes a disease that is fatal in less than 0.04% of cases, while Sars-CoV2 has a CFR (Case Fatality Rate) that is around 1%. Even with highly effective vaccines, the two values would not be comparable.
As for infectivity, the cold has an R0 of about 1.88, which means that a chilled subject will infect about 2 people while in the case of Sars-CoV2 the R0 varies from 2.5 to 18 in the case of the Omicron variant.
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But in addition to these enormous differences in terms of contagiousness and mortality we must consider the pathogenesis. By pathogenesis we mean the mechanism through which the virus generates the pathology: in the case of colds, for example, the above symptoms are given by the response of our immune system and not directly by the virus: the rhinovirus itself is not in fact capable of damaging the organs or structures of our body but simply activates our immune system which reacts and triggers defense mechanisms that manifest themselves in the annoying sneezing and coughing that we know well.
In the case of Sars-CoV2, however, the effects on our body depend both on symptoms triggered by our natural immune response but, unlike the rhinovirus, also on a series of mechanisms that the virus puts in place, damaging our body (such as the formation of syncytia described above). Furthermore, as we know, Sars-Cov2 triggers an absolutely variable symptomatology and an intensity that can be as mild as a simple cold but also very severe.
While mild symptoms may include cough, fever, fatigue, loss of taste and smell, dyspnoea, aphasia, multi-organ failure, pneumonia and death can be seen in severe cases of the same disease.
Furthermore, colds almost exclusively affect the nose, pharynx and larynx while we know that Sars-Cov2 can potentially damage any organ.
The Omicron variant is less lethal but the danger remains
Therefore, if it is true that, as we have seen, the Omicron variant is objectively less lethal than the Delta variant, it is equally true that it has a series of characteristics that make it more dangerous and difficult to manage than a common cold. From a purely epidemiological point of view, we must not forget that a less lethal but more contagious variant can cause more deaths than a more lethal but less contagious variant.
TAKE HOME MESSAGES:
1) The Omicron variant is less lethal than the Delta variant: the risk of hospitalization is one third compared to Delta;
2) The lesser severity is given by the biological characteristics of the variant and by the presence of vaccines;
3) Considering the Omicron variant a common cold is a mistake and constitutes an underestimation of the risk for individuals and for the population;
4) Current triple dose vaccines have been shown to be effective in countering the Omicron variant as well.
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