SARS-CoV-2 is the virus responsible for COVID-19. When this virus enters the body, the immune system responds by producing specialized proteins called antibodies. These antibodies recognize and neutralize foreign invaders like viruses. This article explores SARS-CoV-2 antibodies, how they are detected, their role in immunity, and their application in medical treatments.
Understanding SARS-CoV-2 Antibodies
Antibodies are Y-shaped proteins produced by B cells, part of the adaptive immune system. Upon encountering SARS-CoV-2, B cells activate and differentiate into plasma cells, which produce antibodies. These antibodies bind to unique viral structures, such as the spike protein on SARS-CoV-2’s surface. This binding can block the virus from entering human cells (neutralization) or mark infected cells for destruction.
Different classes of antibodies appear at various stages of an immune response. Immunoglobulin M (IgM) antibodies are among the first, detectable within 1 to 2 weeks after symptom onset. Immunoglobulin A (IgA) antibodies also emerge early and can be found in mucous membranes. Immunoglobulin G (IgG) antibodies develop later, around 2 weeks after illness begins, but persist for longer periods, providing sustained protection.
Detecting SARS-CoV-2 Antibodies
SARS-CoV-2 antibodies are detected through blood tests, often referred to as serology tests. These tests analyze a blood sample to identify antibodies from a past SARS-CoV-2 infection or vaccination. The main purpose of these tests is to confirm a previous infection, assess the immune response after vaccination, or for broader public health surveillance to understand how widely the virus has spread within a population.
Antibody tests differ from diagnostic tests like PCR (polymerase chain reaction) or antigen tests. PCR tests detect the virus’s genetic material, while antigen tests identify specific viral proteins, indicating a current infection. Antibody tests, however, do not diagnose a current infection because it takes time for antibodies to develop after exposure. A positive antibody test indicates that an individual has been infected with SARS-CoV-2 in the past or has been vaccinated. A negative result suggests that the individual may not have had a past infection or sufficient time has not passed for antibodies to develop.
Antibodies and Immunity
The presence of SARS-CoV-2 antibodies is generally associated with some level of protection against future infection or severe disease, though the duration and extent of this protection can vary. Immunity from natural infection may last for over a year, with strong protection against severe outcomes. However, protection against reinfection with milder illness can wane over time, especially with new viral variants.
Vaccine-induced immunity also provides protection. Some studies suggest that mRNA vaccines can elicit higher antibody levels and more durable protection against breakthrough infections compared to natural infection. Vaccine-induced antibody levels can decline over time, leading to the need for booster shots to restore protective antibody levels. Hybrid immunity, from natural infection and vaccination, provides the most robust and long-lasting protection against SARS-CoV-2.
Monoclonal Antibodies in Treatment
Monoclonal antibodies are laboratory-produced antibodies that mimic the body’s natural immune response. For COVID-19, these therapies involve administering antibodies that specifically target the SARS-CoV-2 spike protein, preventing the virus from attaching to and entering human cells. This therapeutic intervention is used to prevent severe illness and hospitalization in high-risk individuals with mild to moderate COVID-19.
Eligibility for monoclonal antibody treatment includes individuals aged 12 years or older who have tested positive for SARS-CoV-2, are experiencing mild to moderate symptoms, and are at high risk of progressing to severe disease. This high-risk category includes individuals with underlying conditions such as older age (e.g., 65 years or older), obesity, diabetes, chronic kidney disease, or those who are immunocompromised. The treatment is administered early in the course of the illness, within 10 days of symptom onset, and is given intravenously. These therapies are not authorized for patients who are hospitalized due to COVID-19 or require oxygen therapy.