Omicron: the different scenarios considered by the Institut Pasteur

The variant Omicron is not yet the majority in France. What face will theepidemic when will it be? Omicron appears much more contagious than Delta, but doubts persist about its severity. The first data from South Africa suggest a 70 to 80% decrease in the risk of hospitalization for Omicron; and the English data, a reduction of 50 to 70% of this same risk, in comparison with the variant Delta.

The Institut Pasteur has just published the results of several mathematical models that predict the number of potential hospitalizations based on assumptions about the severity and transmissibility of Omicron.

Thousands of daily hospitalizations in January?

Considering that Omicron is 80% less severe than Delta, hospitalizations could be controlled with intermediate restriction measures – lowering our contacts by about 20%. Indeed, assuming that Omicron is 67% more contagious than Delta, and 80% less severe, the Institut Pasteur model predicts 2,700 daily hospitalizations without any control measures; 1,400 if the population reduces these contacts by 20%. This peak would be expected for mid-January.

The model also shows that, although Omicron is less severe, nevertheless its high contagiousness is all the more of a threat. If we estimate that it is 84% ​​more transmissible than Delta, and 80% less severe, we could have 4,440 daily hospitalizations by early January if no restrictive measures are taken. Conversely, a 54% more transmissible Omicron variant caused 1,700 daily hospitalizations without restrictive measures.

For an Omicron variant 54% less severe than Delta, the epidemic would remain manageable if intermediate control measures are applied (20% less contact), with 2,500 hospitalizations per day. But this figure explodes if Omicron is 84% ​​more contagious: 5,000 daily hospitalizations at the highest of the peak with the same restrictions.

For simulations where Omicron is as severe as Alpha or Delta, hospitalizations then exceed all hospitalization peaks for 2020 if no strong restriction measures are applied.

Glimpse of a hypothetical future

These computer models depend on the initial assumptions which are not necessarily confirmed by real scientific data. The dynamics of the epidemic are difficult to predict and can change quickly, rendering these predictions obsolete. Scientists have also tested the effect of vaccination on peak hospitalizations.

If the vaccination accelerates, exceeding one million daily injections, the number of hospitalizations could decrease from 9 to 17%. If 90% of the unvaccinated decide to take the plunge, the peak of hospitalizations would decrease from 17 to 35%.

The record of 170,000 contaminations lasted only one day. Yesterday, 208,000 new cases of Covid-19 have been identified. The 5th wave is not ready to stop.