SARS-CoV-2 antibody response in SARS survivors with and without the COVID-19 vaccine

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to spread worldwide. However, it remains unknown whether individuals with prior SARS-CoV-1 infection are protected from SARS-CoV-2 infection. This study assessed protective antibody levels in SARS survivors with and without the COVID-19 vaccine.

We recruited 17 SARS survivors infected with SARS-CoV-1 in 2003, including 8 not vaccinated with the COVID-19 vaccine and 9 vaccinated with two doses of inactivated whole-virion COVID-19 vaccine (Sinopharm). In addition, 105 healthy adult volunteers without SARS-CoV-1 and SARS-CoV-2 infections were used as controls. The relative concentrations of three protective antibodies including anti-SARS-CoV-2 spike IgG (nCoV S-IgG), anti-SARS-CoV-2 spike receptor-binding domain IgG (nCoV RBD-IgG), and anti-SARS-CoV-2 neutralizing antibodies (nCoV NAbs) were measured to evaluate humoral immunity.

We found that the positive rates of these antibodies in unvaccinated SARS survivors were 37.5%, 37.5%, and 62.5%, respectively. In contrast, the corresponding positive rates were all 0% in controls before vaccination. In controls, the levels of protective antibodies reached a peak ca. 28 days after the second dose of vaccine and then started to decline. Surprisingly, the levels of these antibodies were maintained at very high levels even 166 days after the second dose of vaccine in SARS survivors.

Our study suggests that there are protective antibodies cross-reacting with SARS-CoV-2 in recovered SARS patients and that SARS survivors can generate a much stronger antibody response induced by the COVID-19 vaccine than can controls. These initial findings show the feasibility of developing novel pan-sarbecovirus vaccines.