The coronavirus disease (COVID-19) pandemic, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), continues to spread across the globe, with total reported infections now more than 173 million.
To curtail the spread of COVID-19 worldwide, one of the most critical questions is how long the immune response to COVID-19 will last and how potent it will be. The production of antibodies to SARS-CoV-2 contributes significantly to the immune response. Serologic tests to check circulating levels of antibodies are a readily available tool for tracking immune responses in laboratory settings.
Researchers at the National Institutes of Health (NIH), Clinical Center, Department of Transfusion Medicine, Bethesda showed that people who have recovered from COVID-19 might develop naturally acquired immunity that persists for up to 11 months after infection.
The study, published in the Journal of Infectious Diseases, determined how circulating antibody levels change after being infected with SARS-CoV-2.
SARS-CoV-2 infection initiates a humoral immune response that creates antibodies against specific viral antigens such as the nucleocapsid (N) protein and spike (S) protein. These include specific anti-S-protein antibodies that target the spike’s S1 protein subunit and the receptor-binding domain (RBD).
Since SARS-CoV-2 was discovered so recently, relatively few data are available on the long-term kinetics of antibodies. Observations of people who have recovered from a natural infection may provide information on how long antibodies persist after an immunizing exposure, and whether or not these antibodies act as protection against re-infection. In addition, the persistence of antibody responses may help predict the efficacy of COVID-19 vaccines.
In addition, it can also be used to determine the duration of time during which convalescence plasma can be used to treat patients suffering from infections. COVID-19 convalescence plasma (CCP) is an investigational therapy used to prevent disease progression in patients who are battling infection in the hospital. It works by inducing an immune response to boost the body’s protection against the virus.
Importantly, knowing the duration of immunity may provide an opportunity for convalescence plasma donors to return for multiple repeat donations as long as their bodies have anti-SARS-CoV-2 antibodies.
Persists for up to 11 months
In the current study, the researchers followed 228 convalescence plasma donors between April and February 2021. They were assessed for levels of neutralizing antibodies and the total and immunoglobulin G (IgG)-specific S protein antibodies using a lab-developed fluorescent reduction neutralization assay (FRNA) and the VITROS anti-SARS-CoV-2 Total.
The team analyzed the data to determine the link between antibody levels and clinical characteristics, presenting a comprehensive view of SARS-CoV-2 antibody changes over 11 months after being infected with SARS-CoV-2. The purpose of the study was to better understand COVID-19 responses in individuals who obtained the virus in the community.
Before August 2020, the U.S. Food and Drug Administration recommended titers of at least 1:160 for investigational convalescent plasma, but a titer of 1:80 was accepted if higher-titer units were not available.
The study findings revealed that 97 percent of COVID-19 convalescent donors had anti-SARS-CoV-2 antibodies at baseline testing.
In the follow-up visits, 91.4 percent of the 116 donors presenting for repeat timepoints had detectable neutralizing levels up to 11 months after the onset of symptoms. In comparison, 63 percent had detectable neutralizing titers. However, about 25 percent of the donors drop titers of neutralizing levels until these become undetectable over time.
Further, the study showed that most CCP plasma donors, regardless of COVID-19 disease severity, develop antibodies to SARS-CoV-2, and more than 70 percent have neutralizing antibodies.
“Our data suggest that immunological memory is acquired in most individuals infected with SARS-CoV-2 and is sustained in a majority of patients for up to 11 months after recovery,” the researchers concluded in the study.
This means that the body generates sustained immunological memory for most of the first year following SARS-CoV-2 infection, even in mild COVID-19 cases. However, some people may experience a decline in the immunological response against SARS-CoV-2 over the first months following symptom resolution, especially in those who had an asymptomatic or mild illness.
“Efforts are underway to identify the correlates of immunological protection through studying animal models, variable disease outcomes and preexisting immunity to other coronaviruses,” the researchers recommend.
To date, the number of COVID-19 cases continues to rise, with over 33.38 million infections in the United States alone. India and Brazil follow with 28.96 million and 16.94 million cases, respectively.