January 23, 2022

What impact of the Omicron variant on the hospital? The Institut Pasteur readjusts its projections

The researchers revised some of their projections published on December 27, now having “more perspective” on the Omicron variant.

How far will the Omicron wave go? Two weeks after the publication of the first projections on the impact of the variant on hospitalizations in France, the Institut Pasteur posted online this Wednesday an “additional analysis”, dated January 7, which presents updated scenarios, with “more hindsight”.

In it, the researchers repeatedly insist that “the scenarios are made on the basis of incomplete data and uncertain assumptions”, and recall that “the spread of the SARS-CoV-2 virus is difficult to anticipate” .

“Even if the uncertainties are reduced compared to our analyzes of December 27, they remain important as evidenced by the variations observed between the different scenarios presented”, they still write.

In their previous report, the Institut Pasteur considered four scenarios concerning the severity of an infection with Omicron. By virtue of the latest data available on this subject, the researchers now favor two hypotheses: a risk of hospitalization identical to that of the historic virus (-53% compared to Delta), or “twice lower than that of the historic virus ( -77% compared to Delta) “.

A scenario with 2,500 to 3,600 daily hospitalizations

From these conclusions three new scenarios emerge. The former is considered “most likely” by the authors of the report. It postulates a “severity twice as low as that of the historical virus and a high transmissibility” of the Omicron variant.

With this scenario n ° 1, “the peak of hospitalizations could reach 5,200 daily hospitalizations” if the rate of transmission of the virus remains unchanged from the beginning of January. If the French reduce their contacts by 10%, this peak would rise to 3600. If they reduce them by 20%, it would drop to 2500. There are currently a little less than 2200 daily hospitalizations, according to the latest report from the health authorities, dated Tuesday evening.

According to the same breakdown 0% -10% -20%, “we would need respectively 32,000, 23,000 (-27%) and 17,000 (-46%) conventional hospital beds and 6000, 4700 (-23%) and 3900 (- 36%) critical care beds at the peak of the epidemic “. Regarding these last two indicators, the reality has already exceeded the most optimistic projections of the Institut Pasteur, because according to the latest assessment, more than 23,000 people were hospitalized for cases of Covid-19 this Tuesday evening, including 3,969 in intensive care.

Projections of daily Covid-19 hospital admissions (top row), the number of beds in conventional hospitalizations (middle row) and in critical care (bottom row). The red line represents the unchanged transmission rates (0%), the green when they decrease by 10% and the blue 20%.
Projections of daily Covid-19 hospital admissions (top row), the number of beds in conventional hospitalizations (middle row) and in critical care (bottom row). The red line represents the unchanged transmission rates (0%), the green when they decrease by 10% and the blue 20%. © Institut Pasteur

More pessimistic projections

Scenario 3, more pessimistic, postulates a high transmissibility of the Omicron variant but a severity identical to that of the historical virus. In this case, “if the transmission rates are reduced by 0%, 10% and 20% in early January, the peak in hospital admissions would be 8,600, 6,700 (-22%) and 5,100 (-41%), respectively “- figures much higher than the above scenario. And at the peak, it would take “9000, 7400 (-18%) and 6100 (-32%) critical care beds”.

The researchers also investigated, for each of the scenarios, the possibility of “lower vaccine efficacy for Omicron, based on the latest UK data”. The efficacy of the vaccine against infection with Omicron would be no more than 60% within six months of the injection of a booster dose, compared to the 85% previously envisaged.

In this case, the saturation of hospitals would be greater, including with scenario 1: “If the transmission rates are reduced by 0%, 10% and 20% at the beginning of January, the peak of hospital admissions would be of 7200, 5200 (-28%) and 3500 (-52%), respectively “it is underlined. And “at the peak, it would take 43,000, 32,000 (-26%) and 22,000 (-49%) conventional hospital beds and 7,800, 6,000 (-23%) and 4,400 (-44%) critical care beds”.

Regardless, “in all scenarios, peak hospital admissions are expected in the second half of January,” the researchers write, “with maximum impact on bed occupancy in late January-current February” . The peak of infections is expected in mid-January according to these projections.

Salome Vincendon

Salome Vincendon BFMTV reporter