A team of scientists from the United States has recently investigated the robustness and durability of anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies in coronavirus disease 2019 (COVID-19) patients. Their findings reveal that COVID-19 patients exhibit a strong anti-SARS-CoV-2 antibody response for up to 1 year and that the robustness of antibody response depends on the patient’s age and disease severity. The study is currently available on the medRxiv* preprint server.

Background

With more than one year into the COVID-19 pandemic, it is now known that the robustness and durability of anti-SARS-CoV-2 antibody response in COVID-19 patients is a major predictor of reinfection and vaccine response. In this context, studies have shown that even a single vaccine dose is capable of inducing a strong antibody response in individuals with prior SARS-CoV-2 infection.

Similarly, there is evidence showing that the robustness of antibody response positively correlates with the severity of COVID-19. However, cases of reinfection in COVID-19 recovered patients have also been documented in the literature.

Moreover, a limited number of studies have suggested that cross-reactive immunity from seasonal human coronaviruses can provide some degree of protection against SARS-CoV-2 infection. Therefore, an in-depth understanding of the dynamics of anti-SARS-CoV-2 antibody response is particularly necessary to determine the risk of reinfection and vaccine efficacy.

In the current study, the scientists have evaluated the magnitude and durability of IgG-specific anti-SARS-CoV-2 binding and neutralizing antibodies in mild, moderate, or severe COVID-19 patients. They have also investigated whether age, disease severity, and prior immunity against seasonal coronaviruses can influence SARS-CoV-2 specific humoral immunity.

Study design

The study was conducted on laboratory-confirmed COVID-19 patients who received medical treatment at seven military hospitals in the United States. The serum samples were collected from the patients at the time of enrollment and up to one year post-enrollment.

A total of 505 patients (both hospitalized and non-hospitalized) were enrolled for the study and evaluated for anti-SARS-CoV-2 antibody response. The patients were divided into three age groups: 18 – 44 years; 45 – 64 years; and more than 65 years. The patients who had been hospitalized were considered having moderate to severe COVID-19.  

The serum levels of IgG-specific anti-spike binding antibodies were estimated in 250 of 505 enrolled patients. The magnitude and durability of neutralizing antibodies were evaluated in 72 patients within 6 months after the symptom onset. The serum samples collected from 11 patients at 12-month post symptom onset were also evaluated for neutralizing antibodies.

Antibody response and disease severity

The study findings revealed that 100% of hospitalized patients were present with anti-SARS-CoV-2 antibody response even after one year of symptom onset. Among non-hospitalized patients, about 95% and 80% remained seropositive 6 months and 12 months after the symptom onset, respectively. The half-life of binding antibodies in both hospitalized and non-hospitalized patients was found to be more than 1000 days after the symptom onset. During the early infection phase, hospitalized patients exhibited significantly higher antibody levels than non-hospitalized patients. However, after 12 months of infection, this difference in antibody response was abolished.

Two different neutralization assays were carried by the scientists to determine the duration and efficacy of anti-SARS-CoV-2 neutralizing antibodies. In one experiment, the half-life of neutralizing antibodies in hospitalized and non-hospitalized patients was found to be 88 days and 77 days, respectively.

Whereas, in the other experiment, the half-life was estimated to be 106 days and 29 days in hospitalized and non-hospitalized patients, respectively. Similar to the binding antibody response, hospitalized patients exhibited higher neutralizing antibody titers than non-hospitalized patients during the early infection phase. Taken together, these findings reveal a positive correlation between disease severity and antibody response.  

Antibody response and patient age

During the early infection phase, a positive correlation between the binding antibody level and age was observed in non-hospitalized patients. The highest antibody response was observed in non-hospitalized patients aged more than 65 years. Importantly, no difference in antibody response was observed after 12 months of the symptom onset.

The half-life of binding antibodies in non-hospitalized patients aged 18 – 44 years, 45 – 64 years, and more than 65 years were estimated to be 1000 days, 230 days, and 143 days, respectively. However, a half-life of 1000 days was detected in hospitalized patients across all age groups.

Regarding neutralizing antibodies, the magnitude of response was found to increase with age in non-hospitalized patients during the early infection phase. Similarly, higher levels of neutralizing antibodies were observed in non-hospitalized patients aged 45 years and above.

Overall, these findings indicate that the age-dependent increase in early antibody response is confounded by age-related disease severity.

Cross-reactive immune response

During the early infection phase, higher levels of cross-reactive antibodies against seasonal beta coronaviruses were detected in mild to severe COVID-19 patients. However, cross-reactive immune responses to seasonal coronaviruses did not show any correlation with COVID-19 severity and anti-SARS-CoV-2 neutralizing antibody response.

Study significance

The study findings reveal that the antibody-mediated immunity developed in response to natural SARS-CoV-2 infection can persist for up to one year post-infection. However, the robustness and durability of antibody response is relatively lower among younger individuals with mild COVID-19 that does not require hospitalization.

*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

Dr. Sanchari Sinha Dutta

Dr. Sanchari Sinha Dutta is a science communicator who believes in spreading the power of science in every corner of the world. She has a Bachelor of Science (B.Sc.) degree and a Master's of Science (M.Sc.) in biology and human physiology. Following her Master's degree, Sanchari went on to study a Ph.D. in human physiology. She has authored more than 10 original research articles, all of which have been published in world renowned international journals.