New Guide: The American College of Physicians Discusses Antibody Response in COVID-19 Immunity

Due to the novelty of the coronavirus that causes COVID-19, there is not enough evidence to determine whether antibodies produced after exposure will protect against re-infection. That is why the American College of Physicians (ACP) published quick, evidence-based life points in the Annals of Internal Medicine, which discussed the role of antibodies, tests to diagnose, and tests to estimate the prevalence of COVID-19.

Exercise 1: Antibody tests for the COVID-19 diagnosis

The ACP does not recommend using SARS-CoV-2 antibody tests to diagnose COVID-19. This recommendation is based on the limited evidence suggesting that not all patients with COVID-19 develop antibodies at the onset of their infection because the presence and amount of antibodies vary between patients and can be determined by certain disease characteristics.

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The policy panel adds that doctors and patients should be aware that some SARS-CoV-2 antibody tests can give false positive results caused by cross-reactivity with antibodies from other coronaviruses.

Studies also suggest that the sensitivity, specificity, and accuracy of the antibody tests currently available vary widely, further complicating their use as reliable diagnostic tools. Variations in the sensitivity and specificity of these tests can lead to both false negative and false positive results, leading to inaccurate conclusions about infection and possible inadequate or inadequate treatment.

Exercise 2: Antibody tests to estimate the prevalence in the community

Studies suggest that patients develop immune responses after exposure to the new coronavirus. The evidence shows that the majority of patients infected with the SARS-CoV-2 virus have immunoglobulin (Ig) A and IgM antibodies. Almost all patients also show detectable IgG and neutralizing antibodies.

Over time, the prevalence and levels of these antibodies can vary depending on the patient’s characteristics, disease symptoms, and disease severity. On average, levels of each type of antibody peak between 20 and 31 days after the onset of symptoms or diagnosis of the polymerase chain reaction. Studies also show that IgM antibodies can persist for up to 115 days and neutralizing antibodies for up to 152 days. Therefore, the ACP notes that antibody testing could be possible options for estimating the prevalence of COVID-19 in the community.

Exercise point 3: The protective effect of SARS-CoV-2 antibodies against reinfection

There is little evidence that SARS-CoV-2 antibodies confer natural immunity. There is no evidence that SARS-CoV-2 antibodies can predict the presence, degree, or persistence of an conferred natural immunity, particularly with regard to protection against re-infection.

Given that most patients have detectable antibodies for at least 100 days after infection, it may be plausible that natural immunity can occur. However, the panel reiterates that there is no direct evidence to answer the question of whether these antibodies can protect against re-infection.

Some literature suggests that both asymptomatic and symptomatic patients may develop an antibody response that is indicative of natural immunity following COVID-19. However, variables such as the severity of the disease, patient factors, the type and amount of antibodies developed, and the longevity of these antibodies play an important role.

The guideline panel cites a small study in hospital patients with COVID-19 that reported a single possible case of reinfection during the convalescence period. No IgM or IgG antibodies were detected in this patient during the 4-week follow-up period.

Limitations of the practice points

According to the guideline authors, the exercise items presented address only the antibody-mediated natural immune response in COVID-19 and do not specifically address the involvement of other natural immune responses, including cell-mediated immunity or vaccine-acquired immunity.

Currently, the only evidence-based recommendation to increase immunity to the SARS-CoV-2 virus and prevent infection is to get an approved COVID-19 vaccine. Additional prevention strategies recommended in the guideline include social distancing, wearing a mask in public, quarantine, and regular hand washing.

“In view of the limited knowledge about the relationship between antibody levels and natural immunity,” the guideline authors wrote, “patients with SARS-CoV-2 infection and patients with a history of SARS-CoV-2 infection should follow the recommended procedures Adhere to infection prevention and control, slow down and reduce the transmission of SARS-CoV-2. “


Qaseem A, Yost J, Etxeandia-Ikobaltzeta I et al .; for the Scientific Medical Policy Committee of the American College of Physicians. Which antibody response and which role does the conferment of natural immunity play after a SARS-CoV-2 infection? Fast, lively practice points from the American College of Physicians (Version 1). Ann Intern Med. Published online March 16, 2021. doi: 10.7326 / M20-7569

This article originally appeared on Infectious Disease Advisor

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