Antibody response to SARS-CoV-2 vaccination is extremely vivacious in subjects with previous SARS-CoV-2 infection

Abstract

Background: The SARS-CoV-2 pandemic calls for rapid actions, now principally oriented to a world-wide vaccination campaign. In this study we verified if, in individuals with a previous SARS-CoV-2 infection, a single dose of mRNA vaccine would be immunologically equivalent to a full vaccine schedule in naïve individuals. Methods: Health care workers (184) with a previous SARS-CoV-2 infection were sampled soon before the second dose of vaccine and between 7 and 10 days after the second dose, the last sampling time was applied to SARS-CoV-2 naïve individuals, too. Antibodies against SARS-CoV-2 were measured using Elecsys Anti-SARS-CoV-2 S immunoassay. The study was powered for non-inferiority. We used non parametric tests and Pearson correlation test to perform inferential analysis. Results: After a single vaccine injection, the median titer of specific antibodies in individuals with previous COVID-19 was 30,527 U/ml (IQR 19,992-39,288) and in subjects with previous SARS-CoV-2 asymptomatic infection was 19,367.5 U/ml (IQR 14,688-31,353) (P=0.032). Both results were far above the median titer in naïve individuals after a full vaccination schedule: 1,974.5 U/ml (IQR 895-3,455) (P<0.0001). Adverse events after vaccine injection were more frequent after the second dose of vaccine (mean 0.95, 95%CI from 0.75 to 1.14 versus mean 1.91, 95%CI from 1.63 to 2.19)(P<0.0001) and in exposed compared to naïve (mean 1.63; 95%CI from 1.28 to 1.98 versus mean 2.35; 95%CI from 1.87 to 2.82)(P=0.015). Conclusion: In SARS-CoV-2 naturally infected individuals a single mRNA vaccine dose seems sufficient to reach immunity. Modifying current dosing schedules would speed-up vaccination campaigns.