Abstract
Background
We evaluated and compared humoral immune responses after inactivated COVID-19 vaccination among naïve individuals, asymptomatically infected individuals, and recovered patients with varying severity.
Methods
In this multicenter, prospective cohort study, blood samples from 666 participants were collected before and after two doses of inactivated COVID-19 vaccination.
Results
Among 392 SARS-CoV-2-naïve individuals, the seroconversion rate increased significantly from 51.8% (median anti-spike protein pan-immunoglobulins [S-Igs] titer:0.8 U/mL) after the first dose to 96% (median S-Igs titer:79.5 U/mL) after the second dose. 32% of naïve individuals had detectable neutralizing antibodies (NAbs) against the original strain, but all of them lost neutralizing activity against the Omicron variant. In 274 individuals with natural infection, humoral immunity was significantly improved after a single vaccine dose, with median S-Igs titers of 757.8U/mL, 1247.0U/mL, 1280.0U/mL, and 2367.0U/mL for asymptomatic infections, mild cases, moderate cases, and severe/critical cases, respectively. NAb titers also improved significantly. However, the second dose did not substantially increase antibody levels.
Conclusions
Although a booster dose is needed for those without infection, our findings indicate that recovered patients should receive only a single dose of the vaccine, regardless of the clinical severity, until there is sufficient evidence to confirm the benefits of a second dose.
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