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Unvaccinated Convalescent Person with Previous Covid-19 Infection had Low Immunity Response: An Important Clinical Information

Le Ngoc Hung, Nguyen Huu Tung, Cao Hung Phu, Nguyen Van Bac, Nguyen Manh Hoa

When the worldwide population enters the period of vaccination against SARS-CoV-2 infection, the more information on immune response, the better for the prevention strategy against COVID-19. We reported herein the results of SARS-CoV-2 antibodies in a cross-sectional study 75 Vietnamese participants divided into 3 groups: Auninfected person with 2 doses vaccination (“Vac” group; n=32); B: convalescent person who received first dose vaccine then having COVID-19 infection (“Vac-F0” group; n=12); and C: unvaccinated convalescent person with previous COVID-19 infection (“F0” group; n=31). The “F0” group had 26% (8/31) with antibodies higher than 250 U/mL, significantly lower than those from “Vac” group (84.4%, 27/32) and “Vac-F0” group (83.3%, 10/12), p=0.000. There were 3 cases in “F0” group with “no immune response” (<0.4 U/mL, 9.7%). No difference in antibodies between “Vac” and “Vac-F0” group. Among “F0” group, “non-severe infection” person had immune response lower than that from whom with severe infection (p=0.04). Unvaccinated convalescent person with previous infection had low immunity against SARS-CoV-2 virus. The antibody measurement is essential to identify this at-risk population and an additional dose of vaccine is needed for them.