Friday , May 7 2021

70% of SARS-CoV-2 infected in Wuhan still have IgG antibodies

Coronavirus disease (COVID-19) first appeared in late December 2019 in Wuhan, China. Although more than a year has passed since severe acute coronavirus 2 syndrome (SARS-CoV-2) was reported, it is still unclear how long the antibodies last in those who have recovered.

Researchers from Sinopharm Wuhan Biotherapies Co., Ltd. derived from plasma, Ltd. and the Wuhan Institute of Biological Products Co., Ltd. Ltd., showed a positive rate of immunoglobulin G (IgG) antibodies against the domain that binds the protein class (RBD-IgG) receptor to SARS -CoV-2 in convalescent plasma donors COVID-19 exceeded 70 percent for 12 months after infection.

The team also noticed in the study that appeared on the print server in advance bioRkiv*, that the kinetics of RBD-IgG showed a declining trend, with the titer starting to stabilize after nine months and falling by 68.1 percent compared to the first month.

Study background

It has long been a question of how long people who have recovered from COVID-19 have been protected from re-infection. Several SARS-CoV-2 vaccines have been approved worldwide, but it remains unclear how long these vaccines protect against infection.

The persistence of the immune response, especially the humoral immune response, induced by SARS-CoV-2 infection, is essential for understanding the pathogenesis of COVID-19 and predicting the longevity of its vaccine protection.

In infected patients with severe acute respiratory syndrome (SARS), which caused the outbreak in 2002, specific antibodies against the virus can last for an average of two years, with a positive rate and titer of severe acute respiratory syndrome coronavirus 1 (SARS -Cov-1). -specific neutralizing antibodies are significantly reduced in the third year.

Hence, patients with SARS may become susceptible to the same virus three years after recovery from infection. This emphasizes the importance of assessing the persistence of the humoral immune response to the current spreading virus, SARS-CoV-2.


To reach the duration of the humoral immune response in convalescent patients with COVID-19, the researchers conducted a 12-month longitudinal study by collecting 1,782 plasma samples from 869 convalescent plasma donors in Wuhan, China. The team also tested specific antibody responses.

They found that the positive rate of IgG antibodies against the spike protein receptor binding domain to SARS-CoV-2 in COVID-19 convalescent plasma donors exceeded 70 percent for 12 months after infection. This means that the RBD-IgG response in more than 70 percent of convalescent patients with COVID-19 could take about a year, showing that vaccination can help limit the spread of the virus.

The RBD-IgG titer decreased by 69.86 percent in the first year compared to the titer from the first month. The percentage of plasma donors whose RBD-IgG titers remained above the moderate titer at later stages after diagnosis was 27.2 percent.

RBD-IgG titers against SARS-CoV-2 over time.  (A) Percentage changes in positive RBD-IgG.  (B) Changes in RBD-IgG titer distribution.  Titers less than 80 were considered negative.

RBD-IgG titers against SARS-CoV-2 over time. (A) Percentage changes in positive RBD-IgG. (B) Changes in RBD-IgG titer distribution. Titers less than 80 were considered negative.

The team also noted that although the RBD-IgG titer slowly decreased over time during the first year, RBD-IgG became stable at nine months.

Moreover, the researchers assessed the stability of RBD-IgG with different titers based on the titer value early after diagnosis. Even if a faster attenuation of RBD-IgG was observed in plasma donors with elevated titers, after some time, RBD-IgG in plasma donors with high titers remained higher than those with lower titers.

Sequentially, the team found that RBD-IgG titers increased significantly in 11.67 percent of low-titre patients and 1.87 percent of the moderate-titer population during 10 and 11 months. This could be attributed to delayed seroconversion in a small number of plasma donors.

RBD-IgG titers of male plasma donors are higher than those of female plasma donors in the early stages of infection. In the meantime, the elderly may develop an antibody response to SARS-CoV-2, because age is positively associated with RBD-IgG titers.

“Furthermore, we confirmed a positive association between RBD-IgG and neutralizing antibody titers,” the team notes in the study.

“Overall, this study provides strong long-term support for the duration of antibody neutralization protection in plasma donors COVID-19, indicates the potential to prevent re-infection with SARS-CoV-2 and illustrates the role of antibody neutralization in clinical trials and vaccine evaluation,” the team added.

*Important Notice

bioRkiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be considered definitive, lead to clinical practice / health behavior, or be treated as established information.

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