Does the Corona variant Omikron lead to milder disease courses? This question cannot yet be answered with certainty. A statistician explains on Twitter why the impression could arise even without milder viral properties.
The Omikron variant of the coronavirus is currently spreading rapidly not only in South Africa, but also in other countries such as Great Britain and Denmark. that Omikron could also replace the currently prevailing delta variant in Germany at the beginning of next year and thus become the dominant variant. The mutant. It is therefore expected that the virus will lead to more infections in those who have been vaccinated and those who have recovered.
From South Africa, where Omikron first spread, there are indications of milder disease courses due to the virus. Experts,, had recently emphasized that it was too early to make such a statement. Biostatistician Natalie Dean summarized on Twitter why the impression of mild progression could quickly arise with a new variant – even if the disease characteristics were not changed by the virus. Dean is researching the “Rollins School of Public Health” on methods for clinical studies. Her focus is on emerging infectious diseases.
Mild gradients through Omikron could be a fallacy
Dean uses a sketch to illustrate two scenarios. In the first, the virus A circulates in the population. It only results in a few reinfections, i.e. re-infections. Part of the population is thus protected from being infected again – for example, because these people have already gone through an infection and have thus built up an immune protection against the virus. In the part of the population susceptible to the virus, however, some people become seriously ill, some moderately, and still others mildly or asymptomatically.
In the second scenario, virus B is circulating in the population. It differs from virus A in that it leads to significantly more re-infections – for example because, like Omikron, it escapes the antibody protection of vaccinated and convalescents better. Again, in the part of the population susceptible to the virus, some people become seriously ill, others moderately, mildly, or asymptomatically. Now, however, there are also more reinfections in the part of the population that was still protected from infection with virus A. With these breakthrough infections or re-infections, however, milder symptoms are to be expected per se.
In both scenarios, the same number of people will continue to be seriously ill with the virus. With virus B, however, the number of people who get mildly ill is increasing because more people who were still protected from infection with virus A are now becoming infected again.
The sketch serves as an explanation why a new variant could appear milder even without changing the underlying virulence, explains statistician Dean. “This can happen because when calculating the proportion of severe cases, the denominator now contains many reinfections that were previously averted.” This reduces the proportion of severe cases – not because there are less severe cases, but because there are more mild cases in the form of reinfections.
In the coming weeks it should become clear whether Omikron actually leads to milder diseases – or whether this impression is simply based on the ability of the virus to lead to more re-infections. The former would be desirable.
Source From: Stern
