Analysis of immunization time, amplitude, and adverse events of seven different vaccines against SARS-CoV-2 across four different countries. (preprint)

Background: Scarce information exists in relation to the comparison of seroconversion and adverse events following immunization (AEFI) with different SARS-CoV-2 vaccines. Our aim was to correlate the magnitude of the antibody response to vaccination with previous clinical conditions and AEFI. Methods: A multicentric comparative study where SARS-CoV-2 spike 1-2 IgG antibodies IgG titers were measured at baseline, 21-28 days after the first and second dose (when applicable) of the following vaccines: BNT162b2 mRNA, mRNA-1273, Gam-COVID-Vac, Coronavac, ChAdOx1-S, Ad5-nCoV and Ad26.COV2. Mixed model and Poisson generalized linear models were performed. Results: We recruited 1867 subjects [52 (SD 16.8) years old, 52% men]. All vaccines enhanced anti-S1 and anti-S2 IgG antibodies over time (p<0.01). The highest increase after the first and second dose was observed in mRNA-1273 (p<0.001). There was an effect of previous SARS-CoV-2 infection; and an interaction of age with SARS-CoV-2, Gam-COVID-Vac and ChAdOx1-S (p<0.01). There was a negative correlation of Severe or Systemic AEFI (AEs) of naive SARS-CoV-2 subjects with age and sex (p<0.001); a positive interaction between the delta of antibodies with Gam-COVID-Vac (p=0.002). Coronavac, Gam-COVID-Vac and ChAdOx1-S had less AEs compared to BNT162b (p<0.01). mRNA-1273 had a higher number of AEFIs. The delta of the antibodies showed an association with AEFIs in previously infected individuals (p<0.001). Conclusions: The magnitude of seroconversion is predicted by age, vaccine type and SARS-CoV-2 exposure. AEs are correlated with age, sex, and vaccine type. The delta of the antibody response is positively correlated with AEs in patients previously exposed to SARS-CoV-2.

The antibody response to SARS-CoV-2 increases over 5 months in patients with anosmia/dysgeusia (preprint)

The factors involved in the persistence of antibodies to SARS-CoV-2 are unknown. We evaluated the antibody response to SARS-CoV-2 in personnel from 10 healthcare facilities and its association with individuals' characteristics and COVID-19 symptoms in an observational study. We enrolled 4735 subjects (corresponding to 80% of all personnel) over a period of 5 months when the spreading of the virus was drastically reduced. For each participant, we determined the rate of antibody increase or decrease over time in relation to 93 features analyzed in univariate and multivariate analyses through a machine learning approach. In individuals positive for IgG (>= 12 AU/mL) at the beginning of the study, we found an increase [p= 0.0002] in antibody response in symptomatic subjects, particularly with anosmia/dysgeusia (OR 2.75, 95% CI 1.753 - 4.301), in a multivariate logistic regression analysis. This may be linked to the persistence of SARS-CoV-2 in the olfactory bulb.

A cautionary note on recall vaccination in ex-COVID-19 subjects (preprint)

Currently approved COVID-19 vaccines based on mRNA or adenovirus require a first jab followed by recall immunization. There is no indication as to whether individuals who have recovered from COVID-19 should be vaccinated, and if so, if they should receive one or two vaccine doses. Here, we tested the antibody response developed after the first dose of the mRNA based vaccine encoding the SARS-CoV-2 full-length spike protein (BNT162b2) in 124 healthcare professionals of which 57 had a previous history of COVID-19 (ExCOVID). Post-vaccine antibodies in ExCOVID individuals increase exponentially within 7-15 days after the first dose compared to naive subjects (p<0.0001). We developed a multivariate Linear Regression (LR) model with l2 regularization to predict the IgG response for SARS-COV-2 vaccine. We found that the antibody response of ExCOVID patients depends on the IgG pre-vaccine titer and on the symptoms that they developed during the disorder, with anosmia/dysgeusia and gastrointestinal disorders being the most significantly positively correlated in the LR. Thus, one vaccine dose is sufficient to induce a good antibody response in ExCOVID subjects. This poses caution for ExCOVID subjects to receive a second jab both because they may have a overreaction of the inflammatory response and also in light of the current vaccine shortage.