The novel coronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and coronavirus disease 2019 (COVID-19) are new global problems. The understanding of the host immune response in COVID-19 and its implications in the development of therapeutic agents are new challenges. Here, we evaluated the development of immunoglobulin G (IgG) and neutralizing (Nt) antibodies in symptomatic hospitalized COVID-19 patients. We followed up 117 COVID-19 confirmed patients from a reference health center for COVID-19 during the epidemic in Santiago de Chile. One and two sequential blood samples from 117 to 68 cases were, respectively, obtained to evaluate the immune response. Immunofluorescence and neutralization assays in Vero E6 cells with a Chilean SARS-CoV-2 strain were performed. Out of the 68 patients, 44% were women and 56% men, and the most frequent comorbidities were hypertension (47.7%) and diabetes (27.4%). The most frequent symptoms or signs related to COVID-19 were dyspnea, cough, fever, myalgia, and headache. In all the study population, 76.1% and 60.7% of patients were positive for IgG and Nt antibodies in the first blood sample. All patients except one were positive for IgG and Nt antibodies in the second sample. IgG and Nt antibodies positivity increased significantly according to the disease evolution periods. Higher Nt antibody titers were observed in the first sample in patients under 60 years of age. Obese and diabetic patients had no increase in Nt antibodies, unlike normal weight and diabetes-free patients. Both hypertensive and normotensive patients showed a significant increase in Nt antibodies. These results show an early and robust immune response against SARS-CoV-2 infection during severe COVID-19.