Fig. 1

Recruitment of participants, testing, and follow-up. This study included a prospective cohort of residents of long-term care facilities (LTCFs), outpatients, and healthcare workers. During the study period (March 5, 2021, to July 6, 2022), the participants provided peripheral blood samples for serological assays at five time points before and during the 48 weeks after receiving the first vaccine dose: during the baseline period (before the first vaccine dose) and at 8 weeks (period 1), 12 weeks (period 2), 24 weeks (period 3), and 48 weeks (period 4) after the first dose. From the baseline to period 1, one participant refused to complete the two vaccination doses and was excluded from the final analysis. The remaining participants completed two vaccination doses with BNT162b2 (Pfizer-BioNTech) COVID-19 vaccine in the primary vaccine series (two intramuscular doses of 30 mcg each were given three weeks apart) from baseline to period 1. From periods 3 to 4, two participants failed to receive booster vaccination and were excluded from the final analysis in period 4. The remaining participants received booster vaccination from periods 3 to 4. Therefore, the assessment at 48 weeks after the first dose constituted an assessment approximately 3 months after the booster vaccination, wherein all healthcare workers, 14 out of 26 outpatients, and 15 out of 50 LTCF residents received the BNT162b2 (Pfizer-BioNTech) COVID-19 vaccine and 12 out of 26 outpatients and 35 out of 50 LTCF residents received the mRNA-1273 (Moderna) COVID-19 vaccine. Vaccine types for booster vaccination for healthcare workers and LTCF residents were specified by local governments