Antibodies against Covid-19 remained in Covid-19 patients for at least one year, even in those with mild symptoms, a medical report said.

The research team of the Seoul National University Hospital and Pusan National University Hospital released the analysis on antibodies of 52 Covid-19 patients with mild symptoms in the Journal of Korean Medical Science.

The researchers evaluated the antibody response by collecting serum samples of the 52 patients one year after isolation at the community treatment center run by the SNUH from March 5 to April 9.

The research team measured antibodies using four authorized antibody detection kits – Roche Diagnostics’ anti-N pan-Ig ECLIA (electrochemiluminescence immunoassay), InBios’ anti-S IgG ELISA, Euroimmun’s anti-S1 IgG ELISA, and GenScript’s sVNT(surrogate virus neutralization test).

The results showed that the patients with mildly symptomatic Covid-19 infection still had the antibody response one year after the infection.

Anti-N pan-Ig, anti-S IgG, and anti-S1 IgG were detected in 43 patients (82.7 percent), 44 (84.6 percent), and 30 (57.7 percent), respectively. In 49 patients (94.2 percent), the antibody could be detected by either anti-N pan-Ig or anti-S IgG assay. In the sVNT test, 30 (57.7 percent) had positive neutralizing activity.

A U.K. study on healthcare workers showed that Covid-19 anti-N antibodies decreased faster, but anti-S IgG antibodies were detected stably, the report said.

“The present study demonstrated that despite the possible waning of anti-N antibodies, the anti-N pan-Ig assay could be useful to estimate immunity or seroprevalence up to one year after infection,” the research team said.

“Despite waning immunity, SARS-CoV-2 antibodies can be detected up to one year after infection, even in mild COVID-19 patients,” the researchers concluded.