Estimating the burden of SARS-CoV-2 in France

Abstract

France has been heavily affected by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic and went into lockdown on 17 March 2020. Using models applied to hospital and death data, we estimate the impact of the lockdown and current population immunity. We find that 2.9% of infected individuals are hospitalized and 0.5% of those infected die (95% credible interval: 0.3 to 0.9%), ranging from 0.001% in those under 20 years of age to 8.3% in those 80 years of age or older. Across all ages, men are more likely to be hospitalized, enter intensive care, and die than women. The lockdown reduced the reproductive number from 2.90 to 0.67 (77% reduction). By 11 May 2020, when interventions are scheduled to be eased, we project that 3.5 million people (range: 2.1 million to 6.0 million), or 5.3% of the population (range: 3.3 to 9.3%), will have been infected. Population immunity appears to be insufficient to avoid a second wave if all control measures are released at the end of the lockdown.

Fig. 1. COVID-19 hospitalizations and deaths in France.

(A) Cumulative number of general ward and ICU hospitalizations, ICU admissions, and deaths from COVID-19 in France. The vertical green line indicates the time when the lockdown was put in place in France. (B) Geographical distribution of deaths in France. Number of (C) hospitalizations, (D) ICU admissions, and (E) deaths by age group and sex in France.

Fig. 2. Probabilities of hospitalization, ICU admission, and death.

(A) Probability of hospitalization among those infected as a function of age and sex. (B) Probability of ICU admission among those hospitalized as a function of age and sex. (C) Probability of death among those hospitalized as a function of age and sex. (D) Probability of death among those infected as a function of age and sex. For each panel, the horizontal black line and gray shaded region represent the overall mean across all ages. The boxplots represent the 2.5, 25, 50, 75, and 97.5 percentiles of the posterior distributions.

Fig. 3. Time course of the SARS-CoV-2 pandemic to 11 May 2020.

(A) Daily ICU admissions in metropolitan France. (B) Number of ICU beds occupied in metropolitan France. (C) Daily hospital admissions in metropolitan France. (D) Number of general ward beds (in thousands) occupied in metropolitan France. (E) Daily new infections in metropolitan France (logarithmic scale). (F) Predicted proportion of the population infected by 11 May 2020 for each of the 13 regions in metropolitan France. (G) Predicted proportion of the population infected in metropolitan France. The solid circles in (A) to (D) represent hospitalization data used for the calibration, and the open circles represent hospitalization data that were not used for calibration. The dark-blue shaded areas correspond to 50% credible intervals, and the light-blue shaded areas correspond to 95% credible intervals. The dashed lines in (E) and (G) represent the 95% uncertainty range stemming from the uncertainty in the probability of hospitalization after infection.

Fig. 4. Sensitivity analyses considering different modeling assumptions.

(A) Infection fatality rate (%). (B) Estimated reproduction numbers before (R₀) and during lockdown (R_lockdown$)$. (C) Predicted daily new infections on 11 May. (D) Predicted proportion of the population infected by 11 May. The different scenarios are as follows: “Children less inf,” individuals under 20 years of age are half as infectious as adults; “No Change CM,” the structure of the contact matrix (CM) is not modified by the lockdown; “CM SDE,” contact matrix after lockdown with very high social distancing of the elderly; “Constant AR,” attack rates are constant across age groups; “Higher IFR,” French people are 25% more likely to die than Diamond Princess passengers; “Higher AR DP,” 25% of the infections were undetected on the Diamond Princess cruise ship; “Delay Distrib,”single hospitalization to death delay distribution; “Higher delay to hosp,” 8 days on average between symptom onset and hospitalization for patients who will require ICU admission and 9 days on average between symptom onset and hospitalization for the patients who will not; “14 Deaths DP,” the final passenger of the Diamond Princess in ICU survives. For estimates of IFR and reproduction numbers before and during lockdown, we report 95% credible intervals. For estimates of daily new infections and proportion of the population infected by 11 May, we report the 95% uncertainty range stemming from the uncertainty in the probability of hospitalization given infection.