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Background: Vaccines against SARS-CoV-2 have provided an invaluable resource in the fight against this infection. Given the current vaccine shortage, vaccination programs must prioritize their distribution to the most appropriate segments of the population. Methods: We carried out a prospective cohort study with 63 health care workers (HCWs) from a public General Hospital. We compared antibody responses to two doses of BNT162b2 mRNA Covid-19 vaccine between HCWs with laboratory-confirmed SARS-CoV-2 infection before vaccination (experienced HCWs) and HCWs who were not previously infected (naive HCWs). Results: Seven days after the first vaccine dose HCWs with previous infection experienced a 126 fold increase in antibody levels (GMC 26955 AU; 95% CI 18785-35125). However, in the HCW naive group the response was much lower and only 5 of them showed positive antibody levels (>50 AU). The HCWs with previous infection did not significantly increased their antibody levels after the second dose while there was a significant increase in the naive HCW group (16 fold; GMC 20227 AU; 95% CI: 15179-25275). Approximately two months after completing vaccination, the level of antibodies was much lower in naive HCWs (GMC 6595 AU vs. 25003 AU; p<0.001) Conclusion: The study shows that 10 months after the disease has passed, the immune system is capable of producing a rapid and powerful secondary antibody response after one single dose of the vaccine. This response reflects the persistence of immunological memory and it is independent of whether or not anti-SARS-CoV-2 antibodies are detected in blood. Besides, we found that the second dose does not improve the antibody response in individuals with previous Covid-19 infection. Nonetheless, two months later, the persistence of antibody levels is still higher in the experienced HCWs. These data suggest that immune memory remains for a long time in recovered individuals, and therefore, vaccination in this group could be postponed until immunization of the rest of the population is complete.

Background: In patients (pts) with sick sinus syndrome (SSS), right ventricular apical (RVA) pacing increased the risk of developing atrial fibrillation (AF). However, the mechanism of proarrhythmic effect of RVA pacing remains unclear. Methods: We performed detailed echocardiograhic examination with Tissue Doppler Imaging in 60 pts with SSS (mean age 73A9 years, 42 F) who implanted with DDD pacemakers during atrial and ventricular pacing with atrioventricular interval programmed at 120-150 mesc (ApVp mode) and AAI mode with (ApVs mode) at 70 bpm. Echo measurements were taken after 15 mins of pacing in each mode. The myocardial atrial contraction velocity was measured at annulus of right free wall (Ra), septal (Sa) and lateral free wall (La) respectively. Results: As expected, the AV interval was significantly shorter (118A25 vs.163A45 ms, P=0.002), and QRS duration was longer (146A33 vs.97A26 ms, P,0.001) during ApVp mode as compared with ApVs mode. Although there was no significant difference in left ventricular ejection fraction, left atrial (LA) ejection fraction (50A14 vs.55A14%, P=0.005), LA active emptying fraction (32A17 vs.37A16%, P=0.018) and LA filling fraction (43A13 vs. 48A13%, P=0.007) were all significant improved by 18%, 54% and 18%, respectively during ApVs mode as compared with ApVp mode. Furthermore, atrial myocardial contraction velocities among Ra (14.0A3.8 vs.15.2A4.6cm/s, P=0.026), Sa (7.8A2.6 vs. 8.8A2.8cm/s, P=0.001), and La (8.9A3.2 vs.9.7A2.7cm/s, P=0.020) were also significantly increased during ApVs mode by 12%, 19% and 21%, respectively as compared with ApVp mode (Figure). Conclusions: In pts with SSS, avoidance of RVA pacing during ApVs mode improves LA haemodynamic and mechanical function, which might contribute to a lower risk of development of AF after pacemaker implantation. P773Qualitative and quantitative assessment of 3 novel post-processing methods for enhancing echocardiographic images. Echocardiography, while a prevalent tool for assessing cardiac morphology and function, suffers from a range of artefacts that reduce its diagnostic value. This work qualitatively and quantitatively evaluates 3 novel post-processing methods for enhancing echocardiographic images. Data enhancement is achieved by utilising multiple partially decorrelated instances of a cardiac cycle acquired through a single acoustic window. Such information has until now been largely disregarded during data post-processing. Moreover, unlike past approaches, data enhancement is achieved without filtering out information based on static or adaptive selection criteria. Qualitative assessment using 32 clinical datasets demonstrated (i) suppression of cavity noise, (ii) increase in tissue/cavity contrast, and (iii) visual enhancement of tissue structures previously masked-out by various artefacts (Figure 1). The effect of each post-processing method on the diagnostic value of cardiac ultrasound data was quantitatively assessed by examining the repeatability coefficient variations (via Bland-Altman plots) in clini...

BackgroundAfter exposure to SARS-CoV-2 and/or vaccination there is an increase in serum antibody titers followed by a non-linear waning. Our aim was to find out if this waning of antibody titers would fit to a mathematical model.MethodsWe analyzed anti-RBD (receptor binding domain) IgG antibody titers and the breakthrough infections over a ten-month period following the second dose of the mRNA BNT162b2 (Pfizer-BioNtech.) vaccine, in a cohort of 54 health-care workers (HCWs) who were either never infected with SARS-CoV-2 (naïve, nHCW group, n=27) or previously infected with the virus (experienced, eHCW group, n=27). Two mathematical models, exponential and power law, were used to quantify antibody waning kinetics, and we compared the relative quality of the goodness of fit to the data between both models was compared using the Akaik Information Criterion.ResultsWe found that the waning slopes were significantly more pronounced for the naïve when compared to the experienced HCWs in exponential (p-value: 1.801E-9) and power law (p-value: 9.399E-13) models. The waning of anti-RBD IgG antibody levels fitted significantly to both exponential (average-R2: 0.957 for nHCW and 0.954 for eHCW) and power law (average-R2: 0.991 for nHCW and 0.988 for eHCW) models, with a better fit to the power law model. In the nHCW group, titers would descend below an arbitrary 1000-units threshold at a median of 210.6 days (IQ range: 74.2). For the eHCW group, the same risk threshold would be reached at 440.0 days (IQ range: 135.2) post-vaccination.ConclusionTwo parsimonious models can explain the anti-RBD IgG antibody titer waning after vaccination. Regardless of the model used, eHCWs have lower waning slopes and longer persistence of antibody titers than nHCWs. Consequently, personalized vaccination booster schedules should be implemented according to the individual persistence of antibody levels.

Objective. Serum antibody levels have been linked to immune protection in SARS-CoV-2 infection. After exposure to the virus and/or vaccination there is an increase in serum antibody titers followed by progressive non-linear waning of antibody levels. Our aim was to find out if this waning of antibody titers would adjust to a mathematical model. Methods. We studied serum anti-RBD (receptor binding domain) IgG antibody titers over a ten month period in a cohort of 54 health-care workers who were either never infected with SARS-CoV-2 (naive, nHCWs group, n = 27) or previously infected (experienced, eHCWs group, n = 27) with the virus after the second dose of the BNT162b2 mRNA vaccine. We have selected a risk threshold of 1000 UA/ml anti-RBD Ab titer for symptomatic infection based on the upper titer threshold for those volunteers who suffered infection prior to the omicron outbreak. Two mathematical models, exponential and potential, were used to quantify antibody waning kinetics and the relative quality of the goodness of fit to the data between both models was compared using the Akaike Information Criterion. Results. We found that the waning of anti-RBD IgG antibody levels adjusted significantly to both exponential and potential models in all participants from both the naive and experienced groups. Moreover, the waning slopes were significantly more pronounced for the naive when compared to the experienced health-care workers. In the nHCWs group, titers would descend below this 1000-units threshold at a median of 210.6 days (IQ range: 74,2). However, for the eHCWs group, the risk threshold would be reached at 440.0 days (IQ range: 135,2) post-vaccination. Conclusions. The goodness of the fit of the anti-RBD IgG antibody waning would allow us to predict when the antibody titers would fall below an established threshold in both naive and previously infected subjects.