Stable neutralizing antibody levels 6 months after mild and severe COVID-19 episodes

BACKGROUND: Understanding mid-term kinetics of immunity to SARS-CoV-2 is the cornerstone for public health control of the pandemic and vaccine development. However, current evidence is rather based on limited measurements, losing sight of the temporal pattern of these changes. METHODS: We conducted a longitudinal analysis on a prospective cohort of COVID-19 patients followed up for >6 months. Neutralizing activity was evaluated using HIV reporter pseudoviruses expressing SARS-CoV-2 S protein. IgG antibody titer was evaluated by ELISA against the S2 subunit, the receptor binding domain (RBD), and the nucleoprotein (NP). Statistical analyses were carried out using mixed-effects models. FINDINGS: We found that individuals with mild or asymptomatic infection experienced an insignificant decay in neutralizing activity, which persisted 6 months after symptom onset or diagnosis. Hospitalized individuals showed higher neutralizing titers, which decreased following a 2-phase pattern, with an initial rapid decline that significantly slowed after day 80. Despite this initial decay, neutralizing activity at 6 months remained higher among hospitalized individuals compared to mild symptomatic. The slow decline in neutralizing activity at mid-term contrasted with the steep slope of anti-RBD, S2, or NP antibody titers, all of them showing a constant decline over the follow-up period. CONCLUSIONS: Our results reinforce the hypothesis that the quality of the neutralizing immune response against SARS-CoV-2 evolves over the post-convalescent stage. FUNDING: This study was funded by 10.13039/501100016387Grifols, the Departament de Salut of the Generalitat de Catalunya (grant nos. SLD016 to J.B. and SLD015 to J.C.), the Spanish Health Institute Carlos III (grant nos. PI17/01518 and PI18/01332 to J.C.), CERCA Programme/Generalitat de Catalunya2017 SGR 252, and the crowdfunding initiatives #joemcorono, BonPreu/Esclat, and Correos. The funders had no role in the study design, the data collection and analysis, the decision to publish, or the preparation of the manuscript. E.P. was supported by a doctoral grant from the National Agency for Research and Development of Chile (ANID; 72180406). C.A.-N. was supported by a doctoral grant from Generalitat de Catalunya and Fons Social Europeu (FI). S.P.-Y. was supported by 10.13039/501100011850Fundación Canaria Doctor Manuel Morales and 10.13039/100015528Universidad de La Laguna.