A new set‐up of vanishing antibodies: A biennial follow‐up of five different clients' humoral responses against SARS‐CoV‐2 after systemic vaccination in an oncology hospital in Poland

INTRODUCTION The common severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus has infected approximately 600 million people across 228 countries worldwide, leaving behind natural immunity. 1 Acute COVID-19 infection can cause a cytokine storm that leads to acute respiratory failure (ARDS) and death, 2 while severe inflammatory disease can result in chronic polymyositis syndrome in children (PIMS). 3 Almost half (44.8%) of symptomatic infections in children and adults manifest as varied symptoms related to chronic infection, in the form of long-COVID/post-COVID clinical syndrome, cognitive and physical deficits, pulmonary fibrosis, myocarditis, or neurological deficits. 4,5 The findings so far show that to acquire antiviral immunity to SARS-CoV-2, one does not need to come into contact with the virus and become infected. 6 Being around immunized people can provide a cellular and humoral response. 6 IgM and IgG antibody levels (SARS-CoV-2-specific) may indicate early- or late-phase infection. 7 Administration of antibody response acquisition during the early phase has only demonstrated therapeutic implications for symptomatic COVID-19 cases, 8 and vaccination of people with a history of SARS-CoV-2 without knowledge of their humoral response is considered safe. 9 In our hospital, most medical staff and patients underwent vaccinations without knowing that they had acquired a humoral response beforehand. 10 The decline in humoral immunity over time following coronavirus infection, including SARS-CoV-2, is typical in mild cases. 11–16 Then, do all infections require antibody monitoring? According to our earlier observations in this population, the cut-off value for SARS-CoV-2 IgG should be >0.2 AU/mL for a positive test result.