• Sung Hee Lim, Seong Hyeok Choi, Ji Youn Kim, Bora Kim, Han Jo Kim, Se Hyung Kim, Chan Kyu Kim, Seong Kyu Park, and Jina Yun.
• Division of Hematology-Oncology, Department of Medicine, Soonchunhyang University, Bucheon Hospital, Bucheon, Korea.
• J. Korean Med. Sci. 2023 May 8; 38 (18): e139e139.

BackgroundA fourth dose of vaccination is known to help reduce the severity and mortality rate of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. The South Korean vaccination guidelines for the fourth dose do not include healthcare workers (HCWs) as priority candidates. We investigated the necessity of the fourth dose in South Korean HCWs based on an 8-month follow-up period after the third vaccination.MethodsChanges in the surrogate virus neutralization test (sVNT) inhibition (%) score were measured at one month, four months and eight months after the third vaccination. The sVNT values were analyzed between infected and uninfected groups, and their trajectories were compared.ResultsA total of 43 HCWs were enrolled in this study. In total, 28 cases (65.1%) were confirmed to be infected with SARS-CoV-2 (presumed omicron variant), and all had mild symptoms. Meanwhile, 22 cases (78.6%) were infected within four months of the third dose (median, 97.5 days). Eight months after the third dose, the SARS-CoV-2 (presumed omicron variant)-infected group showed significantly higher sVNT inhibition than that in the uninfected group (91.3% vs. 30.7%; P < 0.001). The antibody response due to hybrid immunity, provided by a combination of infection and vaccination, was maintained at sufficient levels for more than four months.ConclusionFor HCWs who had coronavirus disease 2019 infection after completing a third vaccination, a sufficient antibody response was maintained until eight months after the third dose. The recommendation of the fourth dose may not be prioritized in subjects with hybrid immunity.© 2023 The Korean Academy of Medical Sciences.

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