Despite milder Omicron cases: Why experts do not give the all-clear

MMild processes – and yet not a harmless cold virus, hope and yet not clear the warning: The Omikron variant now confronts the experts with delicate communication tasks. A good half a dozen new studies with clinical data have become public over the past few days – many of which have not yet been conclusively assessed – all of which point in one direction: Omikron can make you just as sick as Delta, but it does so less often. In addition, fewer infected people fall ill with Covid-19 after being infected with Omikron, but less so severely that they have to be treated clinically. There are therefore good reasons for the scientists to assume that the risk of a severe and fatal course – at least this applies to vaccinated persons – is lower than, for example, with the delta variant, which is currently still dominant in Germany. Nevertheless, almost no expert gave the all-clear.

New model calculation

Joachim Müller-Jung

Editor in the features section, responsible for the “Nature and Science” section.

Why this is so can be seen in one new model calculation from the Institute for Health Metrics and Evaluation (IHME) show in Seattle. Chris Murray’s team has incorporated the omicron findings and propagation waves since the variant appeared at the end of November in its updated projections of the Covid 19 pandemic. The decisive underlying assumption: Thanks to its combination of more than fifty mutations, Omikron is much more contagious than Delta, and especially more infectious for incomplete, unboosted people due to the immune escape of the virus – however, the variant is also less dangerous with regard to the Covid- 19 disease. The consequence: In the next two to three weeks, at least as many infections are to be expected worldwide as estimated in the entire pandemic: a good three billion infections, in January at the height of around 35 million daily.

Since 90 percent of the cases go undetected due to the milder course, i.e. remain without symptoms (compared to 40 percent with the previous variants), the mammoth portion of the omicron wave will go unnoticed, the population will be infested below the threshold of perception. “Fortunately,” said Murray, this huge surge will not be reflected one-to-one in health care. The number of hospital admissions and deaths in the (better vaccinated) northern hemisphere will remain below the waves of infections of the first winter pandemic, thanks to the progress made in vaccination and the infections that have been overcome. But hospital admissions as well as the number of deaths would rise again in the coming months due to the massive number of infections expected. In some countries even massive, because a large part of the population there is still immunologically “naive”, in other words: has not yet come into contact with a vaccine or the virus itself.

3000 hospitalizations daily in England in January

The studies from South Africa show this: there, due to the earlier wave of infections, it is assumed that there is a high level of immunity against the beta variant. Together with the number of people vaccinated, epidemiologists assume that an estimated 90 percent of people in South Africa have at least partial immunity to Omikron. The “older” antibodies and T cells, which still circulate in the blood of many, do not protect perfectly against omicrons and certainly not against infection of the respiratory tract, but they are so good that the majority of those infected do not have to fear becoming ill . The South African group around Cherry Cohen vom National Institute for Communicable Diseases, of the National Health Laboratory Service in Gauteng has compared the comparison of the disease rates at the end of the delta wave with the Covid-19 cases in the first weeks of the Omikron wave in a – so far not scientifically examined – preprint: Conclusion: With 70 to 80 percent the risk is reduced to become so ill that a hospital admission is necessary. However, since the immunity status of those hospitalized was not precisely recorded in the study, it remains unclear what exactly caused the protection against the disease. The researchers suggest that the high level of pre-immunity is likely to play a decisive role. The result is difficult to transfer due to demographic peculiarities: the population in South Africa is younger overall and therefore better immunologically immune than those in Europe, for example.

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