The objective of this study is to estimate the hospitalization rates among individuals infected with SARS-CoV-2 during the first wave of the COVID-19 epidemic in France, and then to estimate the detection capacity of the COVID-19 RT-PCR testing system since its rollout in late May 2020. During the first wave of the COVID-19 epidemic, serological data from the EpiCoV cohort were used to estimate the number of people infected in France. Over the same period, SI-VIC data indicated the number of hospitalizations due to SARS-CoV-2 infection. Cross-referencing these two data sources allows for an estimate of the hospitalization rate among people infected with SARS-CoV-2 during the first wave. This rate is estimated at 2.7% among infected individuals aged 15 and older residing in mainland France, excluding those residing in nursing homes [1] and prisons. It increases exponentially with age, rising from 0.3% among those aged 15–29, to 2.2% among those aged 50–59, and reaching 22.6% among those aged 70 or older. This latter rate appears very high, and the estimate may lack precision given the small number of people who tested positive in the EpiCoV survey within this age group. Regardless of age group, the hospitalization rate is consistently higher among men, with a particularly marked difference among the oldest age groups. It also varies by geographic region, reaching 3.4% in the North [2] compared to 1.7% in the South, which may be partly due to the fact that infected individuals in the North are generally older and may have more comorbidities. The hospitalization rate for nursing home residents affected by COVID-19 during the first wave was 12.3%, which is lower than that of people aged 70 or older living at home. However, the estimation method differs, and the most severe cases in nursing homes do not always result in hospitalization. Starting in late May 2020, SI-DEP data indicate the number of people who tested positive via RT-PCR in France, providing an initial—albeit underestimated—estimate of the number of infected individuals. Consequently, the hospitalization rates calculated by cross-referencing SI-VIC and SI-DEP data between late May and late August are higher than those estimated during the first wave using SI-VIC and EpiCoV, and this holds true for all age groups. The testing system has gradually ramped up, though it has not yet achieved comprehensive detection of infected individuals. Thus, over the period from late August to late November, the calculated hospitalization rates are approaching—while remaining higher than—those observed during the first wave. Assuming that the hospitalization rates by age group estimated from the EpiCoV survey remain unchanged (i.e., there has been no change in the severity of the epidemic or in hospitalization patterns), it is possible to estimate the number of people aged 15 or older, excluding nursing home residents, infected in mainland France through the end of November 2020, based on the number of people hospitalized during that same period. The detection capacity of the testing system can then be estimated by comparing the number of infections estimated in this way to the number of people who tested positive by RT-PCR. We observe that this capacity has increased: rising from 12% in June to 31% in July–August, 45% in September/early October, and 59% from mid-October to late November. Detection capacity varies little with age, except among those aged 70 or older, where it could have reached over 75% during the most recent period. Testing capacity may be overestimated if the applied hospitalization rates are also overestimated. It is possible that hospitalization rates among infected individuals varied during the epidemic, due to different infection dynamics between the two waves, or due to changes in home care that reduced the need for hospitalization.