Vaccination was critical in controlling the transmission of SARS-CoV-2 during the COVID-19 pandemic. Nevertheless, immune responses are also influenced by nutritional and endocrine factors, particularly vitamin D, whose deficiency has been linked to an increased risk and severity of respiratory infections. This study aimed to assess the impact of 25-hydroxyvitamin D (25(OH)D) levels on the humoral immune response to SARS-CoV-2, as measured by specific immunoglobulin G (IgG) antibody levels. Associations with other factors were also explored, including symptoms, pre-existing conditions, COVID-19 history, vaccination status, and medication use during the course of infection. A longitudinal study was conducted with 131 adult patients from Villa del Rosario (Argentina) who tested positive for SARS-CoV-2 between August and December 2021. Data on weight, age, height, gender, symptoms, pre-existing conditions, vitamin D sources, and COVID-19 history were collected upon diagnosis, as well as 30 and 180 days post-diagnosis. Eighty-five percent of the patients experienced mild COVID-19; 65% had low vitamin D levels, and individuals with pre-existing conditions had significantly lower 25(OH)D levels. The highest antibody levels were observed one month after diagnosis. Vaccinated patients exhibited higher specific antibody levels than unvaccinated ones. Those who used palliative medication for symptom control had lower levels of specific antibodies. Finally, antibody levels decreased significantly between day 30 and day 180 post-diagnosis in patients with vitamin D deficiency. These findings emphasize the importance of maintaining adequate vitamin D levels for sustained immune responses, and highlight the role of vaccination in enhancing immune protection against COVID-19.