A quantitative longitudinal study among COVID-19 patients based on the differences in the kinetics of humoral responses of neutralizing antibodies and its correlation with fatal COVID-19 was conducted by Yale-New Haven Hospital between March 18, 2020 and May 27, 2020. 185 participants were hospitalized patients, 44 were non-hospitalized,16 were vaccinated volunteers, and 105 were health care workers who served as uninfected controls for the study. COVID-19 disease severity was scored through review of electronic health records, and a total of 300 plasma samples were collected and ran through both ELISA and neutralizations assays in order to assess antibody profiles. The study found a correlation between anti-spike (s) immunoglobin G (IgG) levels, length of hospitalization, and increased disease severity. This correlation was time dependent, as deceased patients showed slower antibody dynamics compared to discharged patients, even though higher levels were reached later in the disease trajectory. Neutralizing antibody responses developed within 14 days of symptom onset correlated with recovery and improved disease trajectory and those induced later have shown to lose this protective effect. This data suggests that the loss of the protective role of antibodies in fatal COVID-19 is due to their late onset, and antibody-based therapies would be most beneficial within the first two weeks of disease.