In search of protective antibody for coronavirus disease 2019: A retrospective study.

Introduction: The search for a protective antibody titer level to prevent coronavirus disease 2019 (COVID-19) infection, progression, and death is far from over. To date, no specific cut-off values have been established for these protective antibodies or neutralizing antibody (NAb) titers. NAb titers inhibit viral replication. Aim: To find out the prevailing NAb titre which might give protection from COVID-19 infection, or complication arising out of it. Material and methods: The data of COVID-19 patients with NAb titers who underwent reverse transcription polymerase chain reaction and presented with mild symptoms within 3 days after receiving the results were analyzed. The data were obtained from the clinic’s electronic database. Of the recruited patients, 63 were included in the final analysis. All statistical analyses were performed using SPSS v. 21. Results and discussion: A highly significant correlation (negative) existed between circulating NAb titer and duration of fever (P < 0.001); a positive significant correlation existed between the period from the 1st vaccine dose to the period of infection and the NAb titer level (P < 0.001). The NAb titer was significantly higher in the group that received both doses (P = 0.00016). Death and admission due to progression to moderate COVID-19 occurred in the group with a NAb titer of less than 10 U/L. Conclusions: The risk of complications and death due to COVID-19 may increase if the protective antibody level remains less than 10 U/L. The sample size used in this study was relatively small; therefore, this finding cannot be generalized. Hence, more robust studies should be performed to determine the appropriate protective NAb titer levels. [ABSTRACT FROM AUTHOR]