What We Know About COVID-19 Antibodies



As the COVID-19 pandemic continues, there has been a rising focus on antibodies against SARS-CoV-2, the virus that causes COVID-19. Antibodies are proteins that identify and bind to foreign antigens in the blood and trigger an immune response; they neutralize pathogenic viruses and bacteria. During the earlier stages of the pandemic, there was much speculation that SARS-CoV-2 antibodies in recovered patients could offer protection against a secondary infection. This notion of an “immunity passport” suggested that recovered individuals could potentially return to work and resume their daily activities without risk (1). Several research studies have been done in the recent months analyzing SARS-CoV-2 antibody formation and decline, and the neutralizing capabilities of plasma – researchers are trying to determine 

  1. whether antibodies are formed in recovered patients 
  2. how effectively they eliminate the antigen, or the virus.  

We took a look at recent published research findings to help clarify what is currently known about antibodies against the COVID-19. 

Antibodies Found in Recovered Patients

Preliminary studies revealed that almost all individuals develop IgG and IgM antibodies upon infection. IgG and IgM are antibodies produced by the immune system in response to an infection and usually indicate immunity. In a study done in China, all 285 COVID-19 patients developed antiviral immunoglobulin-G (IgG) antibodies within 19 days of onset of symptoms (2). Since all patients had IgG antibodies in their blood, scientists agree that testing for antibodies can be an effective way to diagnose COVID-19. Another study also looked at the neutralizing potential of blood from recovered patients to test if it is effective in fighting the virus. The blood of these patients actually did not have high neutralizing capabilities perhaps due to low concentration of antibodies. However, other rare antibodies that prevent the virus from entering human cells were found in every individual. Thus, perhaps a vaccine that could elicit these rare antibodies could be successful (3). The findings of this study could indicate why plasma therapy from recovered patients has been a somewhat successful treatment option.

Antibodies May Not Indicate Long-Term Immunity

More recent research findings call for caution against the idea that recovered patients may be protected from reinfection. There is a significant reduction in IgG and neutralizing antibody levels in both symptomatic and asymptomatic patients during the early convalescent phase, 8 weeks after discharge from the hospital (4). These findings suggest that if patients have immunity against SARS-CoV-2, it may be short-lived. A recent study in the New England Journal of Medicine showed that patients who recovered from a mild COVID-19 infection showed rapid decay of IgG levels over a 90 day period after onset of symptoms (5). Therefore, it is likely that recovered patients may not have long-term immunity.

While a lot is still unknown about immunity to SARS-CoV-2 and the mechanisms of IgG and neutralizing antibodies, we now know that recovered individuals should not assume protection against reinfection. Although the U.S Food and Drug Administration (FDA) has not approved any particular treatment for COVID-19, physicians have been using plasma from recovered patients as a way to potentially curb the symptoms of COVID-19. Results from preliminary studies show that convalescent plasma therapy (CPT) might show potential for improved clinical symptoms and reduced mortality (6). However, more comprehensive studies are needed to determine the efficacy of CPT and its mechanisms.