Relationship between Antibody Levels and SARS-Cov-2 Reinfection

In this period when mutant strains are increasing all over the world, studies on how much humoral immunity will protect against the Severe Acute Respiratory Syndrome 2 (SARS-CoV-2) are quite limited. The aim of our study is to investigate the positivity and antibody levels of the COVID-19 reverse transcription polymerase chain reaction (RT-PCR) test, the frequency of SARS-CoV-2 re-infection, and the protective antibody level against re-infection.

Patients who were positive for COVID-19 IgG antibody between 1 July and 31 August were included in our study. The COVID-19 RT-PCR test positivity, age, gender and comorbidities of these patients were recorded before this date. The COVID-19 RT-PCR test positivity of these patients was followed from the National COVID-19 Database between September 1, 2020 and February 28, 2021.

1665 patients (female: male 683: 982, mean age 40.6±13.4 years). Among all patients, 14 patients had reinfection and the frequency of reinfection was 0.8%. It was observed that the frequency of reinfection was more frequent in patients with PCR negative (p<0.001). The IgG cut-off value causing reinfection was found to be 11.9 (AUC: 0.844, 79.2% sensitivity, 78.6% specificity) (p<0.001).

Humoral antibodies against SARS-CoV-2 were protective against COVID-19 reinfection, 0.8% of the patients had reinfection and the resultant reinfection was mostly seen in PCR negative patients who were asymptomatic.