COVID-19: Why it’s increasingly difficult to model evolution of epidemic

Persistent uncertainties around the virus, the difficulty of anticipating the behavior of the population and policy decisions complicate the forecasts.

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Last Results emerged on October 8th computers of models of models, who feed the public authorities on the future of the CVIV-19 epidemic. With a “cautious optimism”, they do not provide for significant recovery before the beginning of the year 2022. But everything depends on the climate, the vaccine coverage, the efficiency of the vaccines, the presence of variants, the relaxation of the French … A long list that testifies to the difficulty of seizing, for a year and a half, the epidemic jolts and that the warning summarizes which traditionally introduces these results: “These scenarios are made on the basis of incomplete database and hypotheses. Uncertain (…) The trajectories described depend on the assumptions made; if the hypotheses do not come true, the observed dynamics may be different from the projections. “

“We often tell us that our models predict everything and its opposite and that they are useless, recognizes the Vittoria Colizza modelizer of the National Institute of Health and Medical Research (INSERM), whose work illuminating the public decision since the beginning of the pandemic. But they help us understand what could happen according to different hypotheses. “With also the goal of” lying to these models, so that the worst never arrives, “says The researcher.

If the measures decided by the public authorities, in view of the projections, have avoided the worst scenarios, at several moments of the pandemic, the models appeared dismissed because of many uncertainties. Either on the properties of the virus and its variants, whose transmissibility is difficult to evaluate in real time. Either on the behaviors of the French themselves (respect of barrier gestures or loosening, ducts at risk or overchargement, etc.), delicate to model and anticipate, while they are central to estimate the speed of diffusion of the epidemic . Either, again, on the political decisions, which do not always fall at the time chosen by the models for their calculations.

January-February 2021: a turning difficult to captate

January 29 , The models of the Institut Pasteur and the Inserm publish a note to describe the possible scenarios in France at the exit of the winter, taking into account the presence of the last variant arrived, says Alpha. Growth in progress is expected to be prolonged and only a new confinement would be able to control the epidemic. But Patatras, a few days later, the epidemic is on the contrary by decreasing fast. “Our models were calibrated on hospitalizations, but the impact of the curfew was not yet visible,” says Vittoria Colizza.

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/Media reports.