Since the outbreak of SARS-CoV-2, the body of scientific literature on COVID-19 has rapidly expanded . Current research often focuses on COVID-19 antibodies, which provide valuable information on the continuing spread of the virus, previous infection patterns, and the immune response .
Widespread availability of commercial assays that detect SARS-CoV-2 antibodies has enabled researchers to examine acquired immunity to COVID-19 at the population level . The four major types of antibody tests are rapid diagnostic tests (RDT), enzyme-linked immunosorbent assays (ELISA), neutralization assays, and chemiluminescent immunoassays . Currently, there is no standard antibody test for detecting SARS-CoV-2 antibodies . Antibody tests for SARS-CoV-2 sense the presence of IgA, IgM, or IgG antibodies produced by B cells . IgM antibodies are produced soon after infection, while IgG antibodies are produced later to maintain the immune response to a specific pathogen . IgA is found on mucous membranes and assists the innate immune response . New clinical reports indicate that antibodies against SARS-CoV-2 form between 6 and 10 days after infection, with peak IgM antibody levels at 12 days . These IgM antibodies persist for up to 35 days . In contrast, IgG antibodies peak at 17 days and persist for up to 49 days .
Higher antibody titers have been discovered in men than women, despite women generally having more B cells and producing more antibodies than men . Observed during the acute stage of SARS-CoV-2 infection, higher antibody titers in men correlate with men showing more severe symptoms and experiencing a higher fatality rate . Conversely, women have shown increased resistance against SARS-CoV-2 . This may be due to the enhanced nature of innate antiviral responses, such as those mediated by toll-like receptors, in women .
The relationship between the presence of SARS-CoV-2 antibodies and the risk of subsequent COVID-19 reinfection remains unclear . Data from a recent study completed at the Oxford University Hospitals in the United Kingdom suggests that the presence of SARS-CoV-2 IgG antibodies is associated with a substantially reduced risk of reinfection for 6 months . The researchers performed a prospective longitudinal cohort study of 12,541 health care workers to assess the relative incidence of positive COVID-19 tests in those who were seropositive for SARS-CoV-2 antibodies and in those who were seronegative . Of the 11,364 health care workers who followed up after an initial negative antibody result, 223 received a positive COVID-19 test . Of the 1,265 health care workers who followed up after an initial positive antibody result, only 2 received a positive COVID-19 test . It may be possible that SARS-CoV-2 protective immunity lasts longer than 6 months . In November 2020, there had been more than 30 million confirmed infections, but few documented cases of reinfection with SARS-CoV-2 throughout the world .
An analysis of 20,000 patients with COVID-19 in the United States concluded that convalescent plasma therapy with neutralizing antibodies is safe and may reduce mortality in critically ill patients . Neutralizing antibodies can be passively transferred into patients before or after viral infection to prevent or treat disease . Therapeutic neutralizing antibodies with high specificity and strong affinity to target proteins have been used to treat several viral infections, including Ebola virus and influenza virus . The neutralizing antibodies against SARS-CoV-2 that have been investigated so far all target spike proteins on the surface of the coronavirus . Plasma containing neutralizing antibodies from convalescent individuals infected with SARS-CoV-2 currently is being administered to severely ill patients . Current research finds that transfusion of such plasma to critically ill patients has resulted in reduced or undetectable viral loads and relieved acute respiratory distress syndrome .
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