• Tu Hoang Kim Trinh, Tuan Diep Tran, Duy Le Pham, Vinh Nhu Nguyen, Quan Tran Thien Vu, Toan Duong Pham, Phong Hoai Nguyen, Minh Kieu Le, Diem Dinh Kieu Truong, Vu Anh Hoang, Nghia Huynh, Dat Quoc Ngo, and Lan Ngoc Vuong.
• University of Medicine and Pharmacy at Ho Chi Minh City, Ho Chi Minh, Vietnam.
• Yonsei Med. J. 2024 Sep 1; 65 (9): 501510501-510.

PurposeAlthough some immune protection from close contact with individuals who have coronavirus disease 2019 (COVID-19) has been documented, there is limited data on the seroprevalence of antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in individuals who were in lockdown with confirmed COVID-19 cases. This study investigated immunogenicity against SARS-CoV-2 in household members and people who lived near home-quarantined patients with COVID-19.Materials And MethodsThis cross-sectional study was conducted during the community-based care that took place during lockdowns in District 10, Ho Chi Minh City, Vietnam from July to September 2021. SARS-CoV-2 antibody levels were determined in index cases of COVID-19, household contacts, and a no-contact group from the same area.ResultsA total of 770 participants were included (355 index cases, 103 household contacts, and 312 no contacts). All index cases were unvaccinated, but >90% of individuals in the household and no-contact groups had received ≥1 vaccine dose. SARS-CoV-2 neutralizing antibodies (Nabs) were present in >77% of unvaccinated index cases versus 64%/65.4% in the household/no-contact groups (p=0.001). Antibody concentrations in unvaccinated index cases were significantly higher than those in household contacts and no contacts, with no difference between the latter groups. In all cases, antibody levels declined markedly ≥6 weeks after infection, and failed to persist beyond this time in the household and no-contact groups.ConclusionCommunity-based care may have helped to create community immunogenicity, but Nabs did not persist, highlighting a need for vaccination for all individuals before, or from 6 weeks after, infection with SARS-CoV-2.© Copyright: Yonsei University College of Medicine 2024.

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