Lower probability and shorter duration of infections after Covid-19 vaccine correlate with anti-SARS-CoV-2 circulating IgGs (preprint)

The correlation between immune responses and protection from SARS-CoV-2 infections and its duration remains unclear. We performed a sanitary surveillance at the European Institute of Oncology (IEO) in Milan over a 17 months period. Pre-vaccination, in 1,493 participants, we scored 266 infections (17.8%) and 8 possible reinfections (3%). Post-vaccination, we identified 30 infections in 2,029 vaccinated individuals (1.5%). We report that the probability of infection post-vaccination is i) significantly lower compared to natural infection, ii) associated with a significantly shorter median duration of infection than that of first infection and reinfection, iii) anticorrelated with circulating antibody levels.

Persistence of anti-SARS-CoV-2 antibodies in non-hospitalized COVID-19 convalescent health care workers (preprint)

BackgroundCoronavirus disease-19 (COVID-19) is a respiratory illness caused by the Severe Acute Respiratory Syndrome CoronaVirus 2 (SARS-CoV-2), a novel beta-coronavirus. Although antibody response to SARS-CoV-2 can be detected early during the infection, several outstanding questions remain to be addressed regarding magnitude and persistence of antibody titer against different viral proteins and their correlation with the strength of the immune response, as measured by serum levels of pro-inflammatory mediators. MethodsAn ELISA assay has been developed by expressing and purifying the recombinant SARS-CoV-2 Spike Receptor Binding Domain (RBD), Soluble Ectodomain (Spike), and full length nucleocapsid protein (N protein). Sera from healthcare workers affected by non-severe COVID-19 were longitudinally collected over four weeks, and compared to sera from patients hospitalized in Intensive Care Units (ICU) and SARS-CoV-2-negative subjects for the presence of IgM, IgG and IgA antibodies as well as soluble pro-inflammatory mediators in the sera. ResultsSpecificity and sensitivity of the ELISA assays were high for anti-RBD IgG and IgA (92-97%) and slightly lower for IgM and the Spike and N proteins (70-85%). The ELISA allowed quantification of IgM, IgG and IgA antibody responses against all the viral antigens tested and showed a correlation between magnitude of the antibody response and disease severity. Non-hospitalized subjects showed lower antibody titers and blood pro-inflammatory cytokine profiles as compared to patients in Intensive Care Units (ICU), irrespective of the antibodies tested. Noteworthy, in non-severe COVID-19 infections, antibody titers against RBD and Spike, but not against the N protein, as well as pro-inflammatory cytokines decreased within a month after viral clearance. ConclusionsRapid decline in antibody titers and in pro-inflammatory cytokines may be a common feature of non-severe SARS-CoV-2 infection, suggesting that antibody-mediated protection against re-infection with SARS-CoV-2 is of short duration. These results suggest caution in use serological testing to estimate the prevalence of SARS-CoV-2 infection in the general population.