contaminations, hospitalizations, mortality… What we learn from data from countries already affected by Omicron

“A tidal wave”, “a tsunami”... Several European countries are facing a wave of Covid-19 contamination unprecedented in its scale since the start of the epidemic, carried by the Omicron variant. In France, more than 208,000 people have tested positive in 24 hours, announced the Minister of Health, Olivier Véran, Wednesday, December 29.

In South Africa, where it was identified in November, the trend is declining. In this country, particularly damaged by previous waves, the records of the number of deaths show a much lower human toll than those observed in the past.

In England (United Kingdom) and Denmark, where the Omicron variant has been rife for several weeks, observers are scrutinizing the admissions of Covid-19 patients in hospitals. The number of new patients is increasing in both countries but at much lower levels than those seen in previous waves. Franceinfo takes stock of the epidemic indicators of these three countries, which have already been confronted for several weeks with this new variant of Sars-Cov-2.

A massive but fast wave?

Much more contagious than previous mutations of the SARS-CoV-2, the Omicron variant causes waves of record contamination. But these viral outbreaks could be as rapid as they are massive. At least that’s what the South African example lets hope for. In this country, whose scientists were the first to identify the new variant at the end of November, the wave of contamination caused by Omicron seems to have already passed.

Starting in mid-November, the increase in cases peaked a month later, on December 18, with an average rate of more than 23,000 positive tests per day. But the curve turned as quickly as it skyrocketed. The number of new contaminations has been dropping steadily for two weeks. On December 29, this indicator had fallen to nearly 11,000 positive tests per day on average, a drop of nearly 34% in one week.

This sudden and continuous fall had not been preceded by further restrictive measures, as had been the case in previous waves. Despite calls for re-containment for the holiday season, the South African government has refused to toughen it all up. The authorities contented themselves with maintaining a curfew between midnight and 4 a.m. In addition, the southern hemisphere has entered its summer season since December 21. This period is less conducive to the circulation of the virus, which spreads especially in enclosed and unventilated places.

A less murderous variant?

Is Omicron as dangerous as the other Sars-Cov-2 variants? Three first studies, published on December 22, are intended to be rather reassuring. This work, which has not been peer reviewed, was carried out by three different teams, one in Scotland, the other in London and the third in South Africa. All report a lower severity of Omicron compared to its predecessor, the Delta variant. The London researchers conclude that the risk of hospitalization is reduced by 25%, the Scottish scientists estimate this decrease at 68% and the South African team at 80%.

The mortality figures in South Africa also seem to point in the direction of a less dangerousness of the Omicron variant. As the graph below shows, the death curve of people with Covid-19 in South Africa has only increased slightly in recent weeks. And its proportions are much lower than those observed during the previous wave caused by the Delta variant.

These data should nevertheless be interpreted with caution, given the specific characteristics of the country. The relative youth of the South African population makes it necessary not to extrapolate these data and not to transpose them to the rest of the world. Thus, 50% of the population of South Africa is under the age of 26, while this median value is more around 40 years in the countries of Western Europe. In addition, the South African population could benefit from a stronger natural immunity acquired following the previous waves, which were particularly virulent in this country.

Hospitalizations on the rise …

The very high rates of transmission observed with the new variant nevertheless raise fears of increased pressure in hospitals. On Wednesday, the World Health Organization (WHO) warned of a risk “collapse” hospital systems. The day before, epidemiologist Dominique Costagliola, interviewed by Le Monde (subscribers article), was worried about “signals” from London, where hospitalizations have been on the rise for a few days.

In fact, data from England and Denmark show increases in hospital admissions of patients with Covid-19. In England, more than 1,200 new patients are hospitalized every day, an increase of almost 50% over one week.

In Denmark, more than 120 new patients on average arrive in hospitals every day. This indicator is also up, by nearly 40% over one week.

Faced with this phenomenon, the WHO is sounding the alarm. “A rapid rise in Omicron, like the one we are seeing in several countries, even if combined with a slightly less severe illness, will still lead to a large number of hospitalizations, especially among the unvaccinated.”, thus recalled, Tuesday, Catherine Smallwood, one of the principal persons in charge of the emergency situations of the WHO Europe.

… but below the curves of a year ago

For now, the influx of Covid-19 patients in English and Danish hospitals remains much lower than those observed during the epidemic peaks of winter 2020-2021. As shown in the graph below, in England the hospitalization curve has not yet reached the levels observed a year ago. This while the number of contaminations is however twice as high this winter.

The same phenomenon is observed in Denmark. While the number of new positive tests is currently more than three times the peak of December 2020, new hospital admissions remain at levels below those seen a year ago.

It remains for the experts to determine several points: is this apparently less seriousness related to the characteristics specific to Omicron, or is it due to the fact that it strikes countries with the high vaccination coverage or the population already partially immunized. following previous waves?

In France, the Institut Pasteur published on Wednesday the latest projections calculated by its modellers. These mathematicians have established several scenarios according to the level of contagiousness and severity attributed to Omicron as well as according to the behavior of the French. Assuming a variant 70% more contagious than Delta and an 80% lower risk of hospitalization, the researchers estimated a peak at 2,700 daily hospitalizations if the population does not reduce its contacts. But peak drops to 1,900 and 1,400 daily hospitalizations, an influx considered more manageable, if the French reduce their contacts by 10% and 20% respectively.


* Methodological note: in order to compare the current wave of Covid-19 with previous waves in each country studied, the values ​​of the various indicators (contaminations, deaths, hospitalizations) are expressed as percentages compared to benchmark values ​​expressed in base 100. This method makes it possible to compare easily several sizes between different periods. Thus, for a base 100 on day D, a contamination index evaluated at 110 on day D + 1 means that between day D and day D + 1, the contaminations are greater by 10%.


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