Researchers carried out a study on convalescent plasma collected from recovered Covid-19 patients to understand life of IgG antibodies against coronavirus infection.
For the study, the researchers collected samples up to 34 weeks after recovery. They found IgG antibodies gradually declined with a median half-life of about two months.
Almost all Covid-19 patients develop IgG, IgM, and IgA antibodies to the virus spike protein and nucleocapsid protein. Antibody levels vary depending on disease severity and duration, the study noted.
Previous studies have reported the antibodies can be identified up to eight months after recovery. Other studies have reported antibodies can be detected within a week to three weeks after symptoms are seen. However, there is little information on how the antibody levels change over a longer time.
Some longer-term studies have reported a small decline in IgG antibody levels over eight months, while others have seen a rapid decline in IgM and IgA levels after a month of symptom onset.
Change in antibodies with time
In a new study, researchers studied antibody trends over 34 weeks from plasma collected from 151 adults who had recovered from the disease.
The authors measured the total antibody levels, IgM, and IgA antibodies to the spike protein receptor-binding domain (RBD) and IgG antibodies to the RBD and nucleocapsid protein.
They found that all the samples collected before five weeks of symptom onset had IgG antibodies to the RBD and decreased only a little with time. IgA and IgM antibodies were seen only in about 70 to 75 per cent of the samples and gradually decreased over time.
Antibody levels varied more than 100-fold among the plasma donors, with greater levels seen in hospitalized patients and males compared to females. Up to 22 weeks, the IgG levels decreased steadily and they had a median half-life of 62 and 50 days for anti-RBD anti-nucleocapsid protein, respectively.
The study further found higher IgG levels in patients who were seriously ill compared to those who had only mild symptoms. Thus, severely ill patients are more suited for donating convalescent plasma.
Antibodies are produced over a long time by long-lived plasma cells and memory B cells, which can last the entire lifetime.
The researchers noted that with continued study, it can be determined if antibodies to SARS-CoV-2 are long-lived, similar to those of SARS-CoV, which can be detected even after three years.
Their findings were published in the medRxiv* preprint server.