Neutralization against SARS-CoV-2 Delta/Omicron variants and B cell response after inactivated vaccination among COVID-19 convalescents

Emerging SARS-CoV-2 variants have made COVID-19 convalescents susceptible to re-infection and have raised concern about the efficacy of inactivated vaccination in neutralization against emerging variants and antigen-specific B cell response.To this end,a study on a long-term cohort of 208 participants who have recovered from COVID-19 was conducted,and the participants were followed up at 3.3(Visit 1),9.2(Visit 2),and 18.5(Visit 3)months after SARS-CoV-2 infection.They were classified into three groups(no-vaccination(n=54),one-dose(n=62),and two-dose(n=92)groups)on the basis of the administration of inactivated vaccination.The neutralizing antibody(NAb)titers against the wild-type virus continued to decrease in the no-vaccination group,but they rose significantly in the one-dose and two-dose groups,with the highest NAb titers being observed in the two-dose group at Visit 3.The NAb titers against the Delta variant for the no-vaccination,one-dose,and two-dose groups decreased by 3.3,1.9,and 2.3 folds relative to the wild-type virus,respectively,and those against the Omicron variant decreased by 7.0,4.0,and 3.8 folds,respectively.Similarly,the responses of SARS-CoV-2 RBD-specific B cells and memory B cells were boosted by the second vaccine dose.Results showed that the convalescents benefited from the administration of the inactivated vaccine(one or two doses),which enhanced neutralization against highly mutated SARS-CoV-2 variants and memory B cell responses.Two doses of inactivated vaccine among COVID-19 convalescents are therefore recommended for the prevention of the COVID-19 pandemic,and vaccination guidelines and policies need to be updated.

Dynamics of the SARS-CoV-2 antibody response up to 10 months after infection

COVID-19 caused by SARS-CoV-2 infection has caused substantial morbidity and mortality worldwide and paralyzed the international economy.Understanding the magnitude and duration of the antibody response to SARS-CoV-2 is important to achieve a balance between curbing the pandemic and minimizing adverse effects on society.1 Although the antibody response to SARS-CoV-2 within 9 months has been extensively studied,2,3,4,5,6 little is known about the magnitude and kinetics of antibody responses for over 9 months.Moreover,with limited observations over 9 months(n<100),2,7,8 several studies have produced inconsistent conclusions about antibody dynamics,suggesting different rates of antiviral antibody positivity at the last follow-up.2,7,8 These studies have been limited by a lack of measurement of neutralizing antibodies(NAbs),7 of inclusion of mild or asymptomatic cases,2,8 and of further exploration of potential predisposing factors for antibody dynamics.2,7 Considering the individual heterogeneity(such as disease severity)8 and time-dependent nature1 of the immune response,in-depth characterization of SARS-CoV-2 antibody kinetics across disease severity groups over a long period is urgently needed.Therefore,we repeatedly tested IgM,IgG,viral spike protein receptor-binding dom(anti-RBD)IgG,and NAb titers in COVID-19 patients during a follow-up period of up to 10 months and explored potential predisposing factors of antibody titers during follow-up.