J Korean Med Sci.  2023 May;38(18):e139. 10.3346/jkms.2023.38.e139.

Eight-Month Follow-up After the Third Dose of BNT162b2 Vaccine in Healthcare Workers: The Question of a Fourth Dose

• Lim SH
• Choi SH
• Kim JY
• Kim B
• Kim HJ
• Kim SH
• Kim CK
• Park SK
• Yun J

• KMID: 2542031
• DOI: http://doi.org/10.3346/jkms.2023.38.e139

Abstract

Background
A 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.
Methods
Changes 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.
Results
A 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.
Conclusion
For 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.

Keyword

Omicron; Neutralizing Antibody; Hybrid Immunity; SARS-CoV-2

Figure

• 

  Fig. 1 sVNT inhibition (%) values against the omicron 1 month, 4 months, and 8 months after the third dose of BNT162b2 vaccine. Violin plots of uninfected group (A), group infected within 4 months (B), and group infected after 4 months (C). The P value at the bottom of each graph was found using the Kruskal–Wallis test.sVNT = surrogate virus neutralization test.Asterisks (*) indicate statistically significant differences between the compared groups (*P < 0.001, **P = 0.001).

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