Study finds low SARS-CoV-2 antibody responses in asymptomatic and mild COVID-19 cases

The coronavirus disease 2019 (COVID-19) pandemic continues to spread across the globe. Caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, the disease exhibits an array of clinical outcomes (from asymptomatic to critical).

The majority of cases are asymptomatic or minimally symptomatic, wherein there are no symptoms or only a few manageable ones. These patients recover with management in their homes.

To date, little is known about the frequency of specific symptoms in the general population and how these symptoms predict the magnitude of antibody response to the SARS-CoV-2 infection.

Study: Symptoms of COVID-19 infection and magnitude of antibody response in a large community-based study. Image Credit: NIAID / Flickr

In a new study, published on the medRxiv* preprint server, researchers at Northwestern University in the U.S. noted high rates of asymptomatic and mild infection in a large community-based cohort and low levels of anti-SARS-CoV-2 immunoglobulin G antibody (IgG) in the general population of previously exposed people.

SARS-CoV-2 infection and symptoms

A characteristic of SARS-CoV-2 is that a high proportion of infections are mild or asymptomatic. Asymptomatic infections are those with no symptom after being infected with SARS-CoV-2, while mild cases are those with symptoms that are manageable at home.

For people who have previously been infected with SARS-CoV-2, serological testing can be performed to detect the presence of antibodies. Further, the magnitude of antibody response is linked to the efficacy of neutralization activity in virus challenge tests.

Assays for antibodies against SARS-CoV-2 can be used to detect a previous infection, even if there were no symptoms or a clinical diagnosis. These tests can provide an insight into protection against future re-infection.

To date, little is known about the actual magnitude of the coronavirus pandemic across the globe. There is limited data on the frequency of COVID-19 symptoms in the general population and how symptoms of the infection related to the magnitude of antibody response.

Patterns of symptoms in COVID-19 patients

In the study, the researchers analyzed patterns of symptoms and their relationship with the magnitude of antibody response using a highly sensitive and quantitative assay for IgG antibodies against the SARS-CoV-2 receptor-binding domain (RBD), the structure that binds with the host cell’s angiotensin-converting enzyme 2 (ACE2) receptor.

A community-based approach helps estimate the prevalence of specific symptoms and how they affect the development of immunity in the majority of infected people who recover without the need for hospitalization.

The study involved 3,365 adults who were participating in a community-based seroprevalence study in Chicago, United States. Home-collected dried blood spot samples were collected between June 24 and November 1, 2020.

The study used data from Screening for Coronavirus Antibodies in Neighborhoods (SCAN), wherein residents were recruited from 10 zip codes. These participants were recruited through various platforms – social medial, emails, newspaper advertisements, flyers, and press coverage in local media. After the participants completed the survey form, a kit for collecting a finger stick dried blood spot (DBS) sample was mailed to them.

The participants were asked to report whether they experienced symptoms of COVID-19 after March 1, 2020, including fever or chills, cough, difficulty breathing, sore throat, headache, body pain or muscle pain, runny nose, fatigue, diarrhea, nausea, vomiting, loss of smell or taste, and red or itchy eyes. Comorbidities were also noted, including diabetes mellitus, hypertension, obesity, cardiovascular disease, smoking, and chronic obstructive pulmonary disease (COPD).

The study findings showed that 17.8 percent of the sample was seropositive for SARS-CoV-2, which means these individuals were previously infected with the virus. Also, some symptoms, including loss of smell or taste, shortness of breath, fever, muscle pain, fatigue, cough, diarrhea, and headache were linked to stronger anti-RBD IgG responses among seropositive people.

About 39.2 percent of the infections were asymptomatic and 66.7 percent had two or fewer symptoms.

Overall, the study suggests that there is a low level of immunity in the general population of previously exposed individuals. Most of these cases experienced no or minimal symptoms and were managed at home.

Given the potential complications of low levels of antibodies among those with a mild previous infection for managing the pandemic, further study should explore the observed link between symptomatic infection, disease severity, and antibody titers in recovered individuals.

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Written by

Angela Betsaida B. Laguipo

Angela is a nurse by profession and a writer by heart. She graduated with honors (Cum Laude) for her Bachelor of Nursing degree at the University of Baguio, Philippines. She is currently completing her Master's Degree where she specialized in Maternal and Child Nursing and worked as a clinical instructor and educator in the School of Nursing at the University of Baguio.