Abstract
We conducted a longitudinal study on the serological IgG type SARS-CoV-2 antibody levels in healthy individuals following COVID-19 vaccination. The study included a total of seven participants, comprising men and women aged 28 to 58 years, who received their first dose of the Moderna COVID-19 vaccine (mRNA-1273) in July 2021. The second vaccination was administered one month later and the third eight months later. Post-vaccination antibody levels were measured weekly until the peak was reached, and then at four-week intervals up to 24 weeks post-vaccination. Furthermore, additional assessments were conducted for one participant who received a fourth dose and two participants who became infected with the Omicron variant. The peaks in antibody levels after the second and third doses were observed at one to two weeks and two to three weeks post-vaccination, respectively. While the antibody levels in each individual declined at a steady rate with a certain half-life, the rate of decline was slower after the third dose. In the case of individuals who were infected or received a fourth dose, the half-life further increased. This suggests that changes in immune dynamics occur due to frequent immunization, regardless of vaccination or viral infection. Additionally, graphing the antibody levels using logarithmic transformation allowed for prediction of the antibody level trends. Although multiple measurements are required, they are important for confirming vaccine efficacy and determining the timing of additional vaccinations, especially when abnormalities in antibody acquisition are suspected due to factors such as age, underlying conditions, and individual constitution.
