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70% of SARS-CoV-2 Infected in Wuhan Still have IgG Antibodies

A study published on a pre-print server conducted by researchers at Sinopharm Wuhan Plasma-derived Biotherapies Co., Ltd and Wuhan Institute of Biological Products Co. Ltd, showed a positive rate of IgG antibody against the receptor-binding domain of the spike protein (RBD-IgG) to SARS-CoV-2 in COVID-19 convalescent plasma donors exceeded 70 percent for 12 months after infection.

To arrive at this finding, the researchers performed a 12-month longitudinal study by collecting 1,782 plasma samples from 869 convalescent plasma donors in Wuhan City, China. The team also tested specific antibody responses.

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

The RBD-IgG titer dropped by 69.86 percent in the first year compared with the first month’s titer. The proportion of the plasma donors whose RBD-IgG titers remained above the moderate titer at the later stages after being diagnosed was 27.2 percent.

The team also noted that though the RBD-IgG titer slowly decreased over time within the first year, the RBD-IgG became stable at nine months. Moreover, the researchers evaluated the RBD-IgG stability with various titers based on the titer value early after diagnosis. Even if more rapid attenuation of RBD-IgG was observed in the plasma donors with elevated titers, after some time, the RBD-IgG in plasma donors with high titers remained higher than those with lower titers. Consecutively, the team revealed that the RBD-IgG titers markedly increased in 11.67 percent of low-titer patients and 1.87 percent of the moderate-titer population at 10 and 11 months.

This could be attributed to the delayed seroconversion in a small number of plasma donors. The RBD-IgG titers of male plasma donors are higher than those of female plasma donors at the early phase of infection. Meanwhile, the elderly might develop antibody response against SARS-CoV-2, as age is positively correlated with the RBD-IgG titers.

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