SARS-CoV-2 immunity can sustain for at least eight months, study finds

By Angela Betsaida B. Laguipo, BSNNov 26 2020

How long does immunity to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) last after initial infection? This is one of the important and difficult questions scientists are grappling with today. Fully understanding this central issue has an enormous bearing on the future of public health, the course of the pandemic as well as the efficacy and longevity of future vaccines.

Lasting immunity to SARS-CoV-2, the agent that causes the coronavirus disease 2019 (COVID-19),  is questioned because serum antibodies decline during convalescence. However, functional immunity is mediated by long-lived memory T and B cells.

A new study by researchers at Monash University, Australia, has revealed that people who have been infected with COVID-19 showed sustained protection against reinfection for at least eight months.

Study: Rapid and lasting generation of B-cell memory to SARS-CoV-2 spike and nucleocapsid proteins in COVID-19 disease and convalescence. Image Credit: Yurchanka Siarhei / Shutterstock

This news article was a review of a preliminary scientific report that had not undergone peer-review at the time of publication. Since its initial publication, the scientific report has now been peer reviewed and accepted for publication in a Scientific Journal. Links to the preliminary and peer-reviewed reports are available in the Sources section at the bottom of this article. View Sources

The study, which was published on the open-source medRxiv* preprint server, shows robust evidence for the likelihood that vaccines will work for long periods.

Although some of the antibodies seem to wane with time, the body retained the ability to remember the virus and generate the response needed to prevent serious illness. Experts believe that this type of immunological memory could last for years.

The study

There has been a steep rise in the number of COVID-19 cases, with many countries experiencing second waves of infections as many businesses and schools have reopened amid the easement of lockdown restrictions worldwide.

To date, over 60.49 million people have been infected, and more than 1.42 million have died.

Some studies have shown that after being infected with COVID-19, there is a decline in antibody response within three months.

In the current study, the researchers aimed to determine the longevity of SARS-CoV-2-specific memory B cells in COVID-19 patients.

To arrive at the study’s findings, the researchers characterized the SARS-CoV-2-specific memory B cell compartment using unique sets of the receptor-binding domain (RBD) and nucleoprotein (NCP) antigens.

The team recruited 25 COVID-19 patients and collected 36 blood samples from day four after infection up to day 242.  They measured the systemic memory B cell response to SARS-CoV-2 infection.

The team emphasized that from vaccination studies in mice and humans, local systemic memory B cells are phenotypically different. It was also shown that influenza-specific memory B cells persist in the lungs of mice and play an essential role in protection from reinfection.

“As knowledge of SARS-CoV-2 and human lung immunology evolve, we will gain insight into what is required for a protective response to this respiratory virus. However, we propose that the establishment of systemic immunity will prevent severe systemic COVID-19, and reinfection may be limited to a mild or asymptomatic upper respiratory tract infection,” the researchers explained in the study.

Memory B cells

Circulating RBD- and NCP-specific memory B cells were detected early after infection and persisted over 242 days after the symptoms appeared.

Further, it appeared that early after being exposed, the Ag-specific cells expressed immunoglobulin M (IgM) over time, followed by the predominance of immunoglobulin G (IgG) antibodies.

The antibodies against the virus started to drop after 20 days post-infection. However, all patients continued to retain memory B cells that recognize one of two components of SARS-CoV-2, the spike and nucleocapsid proteins. These virus-specific memory B cells were detected up to eight months after infection.

Studying the SARS-CoV-2-specific memory B cells could potentially be used as a backup marker of humoral immunity in vaccination studies. At present, COVID-19 vaccine trials explore SARS-CoV-2 specific and neutralizing antibodies as markers of vaccine efficacy.

The results of the current study gives a glimpse of hope that candidate vaccines may provide long-lasting protection against SARS-CoV-2. As antibody levels drop when the immune response contracts, IgG memory B cells remain present, showing that SARS-CoV-2 infection triggers long-term humoral immunity.

The authors said that the study results give hope to the efficacy of vaccines against the virus.

“These results are important because they show, definitively, that patients infected with the COVID-19 virus do retain immunity against the virus and the disease,” Menno van Zelm, associate professor at Monash University, said.

“This has been a black cloud hanging over the potential protection that could be provided by any COVID-19 vaccine and gives real hope that, once a vaccine or vaccines are developed, they will provide long-term protection,” he added.

This news article was a review of a preliminary scientific report that had not undergone peer-review at the time of publication. Since its initial publication, the scientific report has now been peer reviewed and accepted for publication in a Scientific Journal. Links to the preliminary and peer-reviewed reports are available in the Sources section at the bottom of this article. View Sources