배경 The rapidity of SARS-CoV-2-specific memory B or T cell response in vaccinated individuals is important for predicting the risk of breakthrough infection. We therefore compared the timing of adequate im- mune responses between the first and booster doses of COVID-19 vaccines in infection-naïve healthcare workers. 방법 We enrolled healthcare workers who received two doses of either the BNT162b2 vaccine or the ChAdOx1 vaccine, all of whom received the BNT162b2 vaccine as the booster dose. S1-IgG antibodies and IFN-γ producing T cell responses were measured before the first dose, 7, 14, and 21 days after the first dose, before the booster dose, and once between 2 to 7 days after the booster dose. Meaningful SARS-CoV-2 S1-specific IgG response was determined as ≥ 100 IU/mL that corresponds with 80% vaccine efficacy, and meaningful SARS-CoV-2-specific IFN-gamma T cell response was defined as increases in T cell response by ELISPOT assays by two-fold or more compared with pre-vaccination. 결과 After the first-dose vaccination, meaningful S1-IgG antibody responses did not appear within 7 days and were elicited within 14 days in the BNT162b2 group and within 21 days in the ChAdOx1 group. After the booster dose, meaningful S1-IgG antibody responses were elicited within 5 days in both groups. Meaningful SARS-CoV-2-specific T cell responses appeared at 7 days after the first dose and at 4 days after the booster dose. 결론 SARS-CoV-2-specific immune responses by memory B cells and T cells may be expected to appear around 4 to 5 days after the booster dose. [ABSTRACT FROM AUTHOR]