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The good, bad and the ugly: Institut Pasteur’s scenarios for Omicron

The French research institute publishes a series of future possible outcomes based on the current data

There still remain many uncertainties regarding the transmissibility and virulence of Omicron Pic: Arif biswas / Shutterstock

The Institut Pasteur research institute has published a series of potential Covid case number and hospitalisation trajectories based on initial findings on the Omicron variant. 

The report, which was published yesterday (December 29), was shared with the government on Monday ahead of its announcement on new measures to tackle the recent surge in Covid cases. 

Read more: France announces 11 new anti-Covid measures

Read more: Covid France: over 208,000 new cases recorded in last 24 hours

There still remain many uncertainties regarding the transmissibility and virulence of Omicron, and so the extrapolated outcomes vary significantly, but the Institut maintains that the booster campaign plays an essential role in avoiding the reintroduction of harsher restrictions.

2,700 daily hospitalisations if nothing changes 

Clinical studies in Scotland and South Africa have suggested that Omicron is 67-84% more transmissible than the Delta variant.

However, it is also believed to be significantly less virulent. The Institut Pasteur estimates that it could be about as severe as previous Covid strains, making it at least 54% and potentially up to 77% less virulent than Delta. 

If this is the case and Omicron is, say, only 67% more transmissible than Delta, the peak in hospitalisations linked to the new variant could reach 2,700 per day if people in France do not adjust their behaviour. 

To put this into context, during the peak of the second wave in winter 2020 there were 2,900 hospital admissions per day. 

However, if people reduce their social contact by 10%, the peak would be limited to 1,900 admissions per day, and to 1,400 if they cut their contacts by 20%.

The number of people being hospitalised may also be curbed as a result of the new measures announced by the government on Monday, which include working from home and capacity limits on large events. 

Read more: Six questions on France’s new anti-Covid measures answered

Another factor which will serve to reduce hospitalisations according to the Institut Pasteur report would be the acceleration of the booster campaign. 

If 1.2 million doses are administered each day, compared to the average of 400,000 which are currently being given, the peak in hospitalisations could be cut by up to 17%. The government is aiming to increase the number of daily booster dose appointments to 1 million in January.

In addition, the Institut Pasteur reports that if 90% of unvaccinated adults chose to receive the vaccine at a rate of 100,000 per day, the peak in hospitalisations could be reduced by 17-35%.

Last week, around 22,000 first vaccine doses were administered each day.

Simon Cauchemez, who leads the Institut Pasteur’s modelling department, told France Inter that Omicron could even be 80% less virulent than Delta. 

However, “the people who are infected with Omicron are potentially more likely to have already been infected by another variant or to have been vaccinated, and so could be protected by these past infections,” he added. 

This means that “it is possible that studies are underestimating the reduction in severity.” 

A more worrying scenario

If Omicron is indeed much less severe than Delta but spreads 84% more quickly rather than 67%, hospital admissions could reach 4,400 per day. 

This would be significantly more than in the first wave, when daily hospitalisations peaked at 3,500, and would mean that people would have to reduce their contacts by 20% to get back to 2,700 admissions a day.

The worst case scenario 

The Institut Pasteur has also modelled the trajectory of the Omicron-related Covid wave based on a more pessimistic view of its virulence. 

It shows that if Omicron is not as mild as currently believed and only 33% less severe than Delta, France could reach 7,000-10,000 hospitalisations each day even with a 20% reduction in social contacts.

If this were to occur, the infection control measures already in place would not be sufficient, and a curfew or even a lockdown would be necessary. 

However, this is not the most likely scenario. 

The Institut has stated that it could be better to wait a few days before deciding whether to take stricter measures against the spread of Omicron, but that waiting too long could cause hospitals to be overwhelmed. 

The government will hold a Conseil de défense sanitaire meeting on January 5, during which they may discuss additional Covid restrictions. 

Related stories 

10% of people in France are Covid contact cases, says health minister

Covid: Face masks obligatory in streets of Paris from December 31

Covid boosters, vaccine passes: What changes in France on January 15?

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