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The use of photothermal processes has been proven effective in the control of microbial infections. Simultaneously, the localized surface plasmon resonance phenomena in metallic nanoparticles have been explored as an alternative strategy to achieve highly efficient localized heating. In this work, we propose the use of selected nanoheaters to improve the efficiency of fungal photothermal inactivation of Candida albicans through size optimization of plasmonic gold nanorods. Here, the optical heating of polyethylene glycol coated gold nanorods of varying sizes is evaluated, both theoretically and experimentally. A size-dependent computational approach was applied to identify metallic nanorods with maximized thermal performance at 800 nm, followed by the experimental comparison of optimal and suboptimal nanoheaters. Comparison among samples show temperatures of up to 53.0 °C for 41×10 nm gold nanorods against 32.3 °C for 90×25 nm, a percentage increase of ∼63% in photothermal inactivation assessments. Our findings reveal that gold nanorods of 41×10 nm exhibit superior efficiency in near-infrared (800 nm) photothermal inactivation of fungi, owing to their higher light-thermal conversion efficiency. The identification of high performance metallic nanoheaters may lead to the reduction of the nanoparticle dose used in plasmonic-based procedures and decrease the laser exposure time needed to induce cell death. Moreover, our results provide insights to better exploit plasmonic nanoparticles on photothermal inactivation protocols., (Copyright © 2024. Published by Elsevier B.V.)

Objective: To develop and validate a predictive model utilizing machine-learning techniques for estimating the length of hospital stay among patients who underwent coronary artery bypass grafting., Methods: Three machine learning models (random forest, extreme gradient boosting and neural networks) and three traditional regression models (Poisson regression, linear regression, negative binomial regression) were trained in a dataset of 9,584 patients who underwent coronary artery bypass grafting between January 2017 and December 2021. The data were collected from hospital discharges from 133 centers in Brazil. Algorithms were ranked by calculating the root mean squared logarithmic error (RMSLE). The top performing algorithm was validated in a never-before-seen database of 2,627 patients. We also developed a model with the top ten variables to improve usability., Results: The random forest technique produced the model with the lowest error. The RMLSE was 0.412 (95%CI 0.405-0.419) on the training dataset and 0.454 (95%CI 0.441-0.468) on the validation dataset. Non-elective surgery, admission to a public hospital, heart failure, and age had the greatest impact on length of hospital stay., Conclusions: The predictive model can be used to generate length of hospital stay indices that could be used as markers of efficiency and identify patients with the potential for prolonged hospitalization, helping the institution in managing beds, scheduling surgeries, and allocating resources.

Objective: To investigate mirror activity in amyotrophic lateral sclerosis (ALS) patients, using a simple paradigm of signal quantification., Methods: Patients were asked to perform a brief isometric maximum contraction of the abductor digiti minimi (ADM) or tibialis anterior (TA) on one side, while relaxing the contralateral side of the body. Both sides were investigated. Signals were stored and analyzed offline, for quantification of electromyographic signal. Clinical signs of upper motor neuron (UMN) dysfunction, transcranial magnetic stimulation (TMS) for the upper (UL) and lower limbs (LL), the ADM ipsilateral cortical silent period (iSP) and the Edinburgh Cognitive and Behavioral ALS Screen (ECAS) cognitive scale were also investigated., Results: 42 ALS patients were included. In the 4 investigated muscles the amount of mirror activity was significantly higher than in the matched healthy group. The amount of mirror activity was similar between sides, but significantly higher in UL and LL with abnormal TMS results for ADM (p = 0.005) and TA (p = 0.002), as well as in UL with abnormal iSP values (p = 0.009). No association was found between mirror activity and clinical signs of UMN involvement., Conclusions: Mirror activity is a common phenomenon in ALS. Mirror activity intensity corresponds to the severity of UMN dysfunction, as measured by TMS, and probably derives from the abnormal transcallosal inhibition as mirrored by iSP abnormality., Significance: Mirror activity is increased in ALS and is associated with abnormal transcallosal inhibition and UMN dysfunction., (Copyright © 2023 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.)

Introduction: Influenza A (H3N2) virus is the major cause of morbidity/mortality due to seasonal influenza over 50 years. Data about the safety/immunogenicity of influenza A/Singapore (H3N2) vaccine are scarce in primary Sjögren syndrome (pSS)., Methods: Twenty-one consecutive pSS patients and 42 HC (healthy control individuals) were immunized with influenza A/Singapore/INFIMH-16-0019/2016 (H3N2)-like virus. Rates of SP (seroprotection) and SC (seroconversion), GMT (geometric mean titers), FI-GMT (factor increase in GMT), ESSDAI (EULAR Sjögren's Syndrome Disease Activity Index), and adverse events were appraised before and 4 weeks post-vaccination., Results: pSS and HC had similar mean age (51.2 ± 14.2 vs. 50.6 ± 12.1 years, p = 0.886). Pre-vaccination SP rates were high in pSS and HC (90.5% vs. 71.4%, p = 0.114), and GMT were higher in pSS [80.0 (52.4-160.0) vs. 40.0 (20.0-80.0), p = 0.001]. The percentage of influenza vaccination in the preceding two years was elevated and similar in pSS and HC (94.1% vs. 94.6%, p = 1.000). GMT values augmented in both groups four weeks after vaccination and persisted higher in the first group [160.0 (80.0-320.0) vs. 80.0 (40.0-80.0), p < 0.001] with equivalent FI-GMT [1.4 (1.0-2.8) vs. 1.4 (1.0-2.0), p = 0.410]. Both groups had low and similar SC rates (19.0% vs. 9.5%, p = 0.423). ESSDAI values persisted steadily during the study (p = 0.313). No serious adverse events have occurred., Conclusion: The novel demonstration that the influenza A/Singapore (H3N2) vaccine induces a different pattern of immunogenicity from other influenza A constituents in pSS, featured by a desirable high pre- and post-vaccination immunogenicity, is in line with reported differences in immune responses between strains in trivalent vaccines and may be related to pre-existing immunity., Clinicaltrials: gov: #NCT03540823. Key Points • This prospective study demonstrated a robust pre- and post-vaccination immunogenicity to influenza A/Singapore/INFIMH-16-0019/2016 (H3N2)-like virus in primary Sjögren's syndrome (pSS). • This high immunogenicity pattern may be related to pre-existing immunization, or else it is related to immunogenicity differences of each strain. • This vaccine had an adequate safety profile in pSS, with no impact on disease activity., (© 2023. The Author(s), under exclusive licence to International League of Associations for Rheumatology (ILAR).)

Mirror activity is an involuntary activation of a muscle when the respective contralateral muscle is contracting. This phenomenon has been described primarily in children and in disease states, and, more recently, also in healthy adults. Different ways of assessing mirror activity have been described. In this work we propose a simple protocol for quantifying the amount of mirror activity during a brief isolated full force isometric contraction of a given muscle. The signal was analyzed by a custom-built algorithm that detects the beginning and the end of muscle contraction. The amount of EMG signal on the mirror muscle in relation to the amount of EMG signal of the active muscle is then calculated. We studied 57 right-handed healthy subjects. Mirror activity was evaluated in the Abductor digiti minimi (ADM) and Tibialis anterior (TA) muscles during a 2-3 s full force isometric contraction. The intensity of mirror movement was represented as a percentage of the signal from maximal voluntary contraction. The performance of the algorithm for the detection of the beginning of muscle contraction was very good, when compared to 2 human operators. Intraclass correlation coefficient was excellent (0.998). The Bland-Altman plots showed similar performances of the algorithm and the human operators. We found a significant correlation of mirror activity with intensity and age. There was significantly more intense mirror activity in the left limbs (non-dominant) when compared to the right limbs. The upper limits of normality for mirror EMG signal was 27.4% for right ADM, 15.4% for left ADM, 10.4% for right TA and 2.1% for left TA. This simple protocol allows for an objective measurement of the amount of mirror activity. We propose this technique for investigation of neurological disorders., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Author(s). Published by Elsevier B.V. All rights reserved.)

Objective: Coronavirus disease 19 (COVID-19) has an increased risk of coagulopathy with high frequency of antiphospholipid antibodies (aPL). Recent reports of thrombosis associated with adenovirus-based vaccines raised concern that SARS-CoV-2 immunization in primary antiphospholipid syndrome (PAPS) patients may trigger clotting complications. Our objectives were to assess immunogenicity, safety, and aPL production in PAPS patients, after vaccinating with Sinovac-CoronaVac, an inactivated virus vaccine against COVID-19., Methods: This prospective controlled phase-4 study of PAPS patients and a control group (CG) consisted of a two-dose Sinovac-CoronaVac (D0/D28) and blood collection before vaccination (D0), at D28 and 6 weeks after second dose (D69) for immunogenicity/aPL levels. Outcomes were seroconversion (SC) rates of anti-SARS-CoV-2 S1/S2 IgG and/or neutralizing antibodies (NAb) at D28/D69 in naïve participants. Safety and aPL production were also assessed., Results: We included 44 PAPS patients (31 naïve) and 132 CG (108 naïve) with comparable age ( p =0.982) and sex ( p >0.999). At D69, both groups had high and comparable SC (83.9% vs. 93.5%, p =0.092), as well as NAb positivity (77.4% vs. 78.7%, p =0.440), and NAb-activity (64.3% vs. 60.9%, p =0.689). Thrombotic events up to 6 months or other moderate/severe side effects were not observed. PAPS patients remained with stable aPL levels throughout the study at D0 vs. D28 vs. D69: anticardiolipin (aCL) IgG ( p =0.058) and IgM ( p =0.091); anti-beta-2 glycoprotein I (aβ2GPI) IgG ( p =0.513) and IgM ( p =0.468)., Conclusion: We provided novel evidence that Sinovac-CoronaVac has high immunogenicity and safety profile in PAPS. Furthermore, Sinovac-CoronaVac did not trigger thrombosis nor induced changes in aPL production.

Objective: To evaluate the effect on immunogenicity and safety of 2-week methotrexate (MTX) discontinuation after each dose of the Sinovac-CoronaVac vaccine versus MTX maintenance in patients with rheumatoid arthritis (RA)., Methods: This was a single-centre, prospective, randomised, investigator-blinded, intervention study (NCT04754698, CoronavRheum) including adult patients with RA (stable Clinical Disease Activity Index (CDAI) ≤10, prednisone ≤7.5 mg/day) randomised (1:1) to withdraw MTX (MTX-hold) for 2 weeks after each vaccine dose or maintain MTX (MTX-maintain), evaluated at day 0 (D0), D28 and D69. Coprimary outcomes were anti-SARS-CoV-2 S1/S2 IgG seroconversion (SC) and neutralising antibody (NAb) positivity at D69. Secondary outcomes were geometric mean titres (GMT) and flare rates. For immunogenicity analyses, we excluded patients with baseline positive IgG/NAb, and for safety reasons those who flared at D28 (CDAI >10) and did not withdraw MTX twice., Results: Randomisation included 138 patients with 9 exclusions (5 COVID-19, 4 protocol violations). Safety evaluation included 60 patients in the MTX-hold and 69 patients in the MTX-maintain group. Further exclusions included 27 patients (13 (21.7%) vs 14 (20.3%), p=0.848) with positive baseline IgG/NAb and 10 patients (21.3%) in MTX-hold with CDAI >10 at D28. At D69, the MTX-hold group (n=37) had a higher rate of SC than the MTX-maintain group (n=55) (29 (78.4%) vs 30 (54.5%), p=0.019), with parallel augmentation in GMT (34.2 (25.2-46.4) vs 16.8 (11.9-23.6), p=0.006). No differences were observed for NAb positivity (23 (62.2%) vs 27 (49.1%), p=0.217). At D28 flare, the rates were comparable in both groups (CDAI, p=0.122; Disease Activity Score in 28 joints with C reactive protein, p=0.576), whereas CDAI >10 was more frequent in MTX-hold at D69 (p=0.024)., Conclusion: We provided novel data that 2-week MTX withdrawal after each dose of the Sinovac-CoronaVac vaccine improves anti-SARS-CoV-2 IgG response. The increased flare rates after the second MTX withdrawal may be attributed to the short-term interval between vaccine doses. This strategy requires close surveillance and shared decision making due to the possibility of flares., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2022. No commercial re-use. See rights and permissions. Published by BMJ.)

Background: People living with HIV might have a poor or delayed response to vaccines, mainly when CD4 cell counts are low, and data concerning COVID-19 vaccines in this population are scarce. This prospective cohort study assessed the safety and immunogenicity of the inactivated SARS-CoV-2 vaccine CoronaVac in people with HIV compared with people with no known immunosuppression., Methods: In this prospective cohort study, adults (aged ≥18 years) living with HIV who were regularly followed up at the University of Sao Paulo HIV/AIDS outpatient clinic in Sao Paulo, Brazil, were included in the study. Eligibility for people with HIV was independent of antiretroviral use, HIV viral load, or CD4 cell count. Adults with no known immunosuppression with CoronaVac vaccination history were included as a control group. CoronaVac was given intramuscularly in a two-dose regimen, 28 days apart. Blood was collected before vaccine administration and 6 weeks after the second dose (day 69). Immunogenicity was assessed at baseline (day 0), before second vaccine (day 28), and 6 weeks after second vaccine dose (day 69) through SARS-CoV-2 IgG titre and seroconversion, neutralising antibody (NAb) positivity and percentage activity, and factor increase in IgG geometric mean titres (FI-GMT). We investigated whether HIV status and CD4 count (<500 or ≥500 cells per μL) were associated with CoronaVac immunogenicity by use of multivariable models adjusted for age and sex., Findings: Between Feb 9, 2021, and March 4, 2021, 776 participants were recruited. Of 511 participants included, 215 (42%) were people with HIV and 296 (58%) were people with no known immunosuppression. At 6 weeks after the second vaccine dose (day 69), 185 (91%) of 204 participants with HIV and 265 (97%) of 274 participants with no known immunosuppression had seroconversion (p=0·0055). 143 (71%) of 202 participants with HIV were NAb positive compared with 229 (84%) of 274 participants with no known immunosuppression (p=0·0008). Median IgG titres were 48·7 AU/mL (IQR 26·6-88·2) in people with HIV compared with 75·2 AU/mL (50·3-112·0) in people with no known immunosuppression (p<0·0001); and median NAb activity was 46·2% (26·9-69·7) compared with 60·8% (39·8-79·9; p<0·0001). In people with HIV who had CD4 counts less than 500 cells per μL seroconversion rates, NAb positivity, and NAb activity were lower than in those with CD4 counts of at least 500 cells per μL. In multivariable models for seroconversion, NAb positivity, IgG concentration, and NAb activity after a complete two-dose regimen, adjusted for age and sex, people with HIV who had CD4 counts of at least 500 cells per μL and people with no known immunosuppression had higher immunogenicity than did people with HIV with CD4 counts less than 500 cells per μL. No serious adverse reactions were reported during the study., Interpretation: Immunogenicity following CoronaVac in people with HIV seems strong but reduced compared with people with no known immunosuppression. Our findings highlight the need for strategies to improve vaccine immunogenicity in people with HIV., Funding: Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), and B3-Bolsa de Valores do Brasil., Competing Interests: Declaration of interests EGK is the Principal Investigator for the CoronaVac phase 3 clinical trial at the University of Sao Paulo. VIA-S is the Principal Investigator for the Janssen COVID-19 vaccine phase 3 clinical trial at University of Sao Paulo. All other authors declare no competing interests., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Objectives: To evaluate the distinct impact of disease modifying antirheumatic drugs (DMARD) combination and monotherapy in immune response to an inactivated SARS-CoV-2 vaccine in patients with rheumatoid arthritis (RA)., Methods: This phase 4 prospective study analysed seroconversion (SC) of anti-SARS-CoV-2 immunoglobulin G (IgG) and neutralising antibodies (NAb) induced by the inactivated vaccine (CoronaVac) in patients with RA in comparison to controls (CG). Disease activity and treatment were also assessed. Only participants with baseline negative IgG/NAb were included., Results: Patients with RA (N=260) and CG (N=104) had comparable median ages (59 years (50-65 years) vs 58 years (49.8-64 years), p=0.483). Patients with RA had moderate but lower SC (61.8% vs 94.2%, p<0.001) and NAb positivity (45% vs 78.6%, p<0.001) in comparison to CG after full vaccination. Baseline disease activity did not influence immunogenicity (p>0.05). After multivariate analyses, factors independently related to reduced SC were: older age (OR=0.79 (0.70-0.89) for each 5-year interval, p<0.001), methotrexate (OR=0.54 (0.29-0.98), p=0.044), abatacept (OR=0.37 (0.19-0.73), p=0.004) and number of DMARD (OR=0.55 (0.33-0.90), p=0.018). Regarding NAb, age (OR=0.87 (0.78-0.96) for each 5-year interval, p=0.007) and prednisone >7.5 mg/day (OR=0.38 (0.19-0.74), p=0.004) were negatively related to the presence of NAb. Further comparison of SC/NAb positivity among RA treatment subgroups and CG revealed that methotrexate/tofacitinib/abatacept/tocilizumab use, in monotherapy or in combination, resulted in lower responses (p<0.05), while tumour necrosis factor inhibitor and other conventional synthetic DMARD interfered solely when combined with other therapies., Conclusions: Patients with RA under DMARD have a moderate immunogenicity to CoronaVac. We identified that nearly all DMARD combinations have a deleterious effect in immunogenicity, whereas a more restricted number of drugs (methotrexate/tofacitinib/abatacept/tocilizumab) also hampered this response as monotherapy. These findings reinforce the need of a broader approach, not limited to specific drugs, to improve vaccine response for this population., Trial Registration Details: NCT04754698., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2022. No commercial re-use. See rights and permissions. Published by BMJ.)

Objective: To date, the only study that has assessed the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2 mRNA) vaccine in systemic lupus erythematosus (SLE) observed a moderate response, but the sample size precluded an accurate analysis of the effect of individual drugs. Therefore, we evaluated the immunogenicity of an inactivated SARS-CoV-2 vaccine (Sinovac-CoronaVac) and the influence of different medications in SLE. Safety was also assessed., Methods: We conducted a prospective controlled study of 232 SARS-CoV-2-naive SLE patients and 58 SARS-CoV-2-naive controls who were vaccinated with 2 doses of Sinovac-CoronaVac with a 28-day interval (day 0/day 28 [D0/D28]). Immunogenicity analysis at D0/D28 and D69 included anti-SARS-CoV-2 S1/S2 IgG seroconversion (SC) and neutralizing antibodies (NAb) positivity. The influence of individual drugs on immune response and safety was assessed., Results: Patients and controls were well balanced for age (P = 0.771). At D69, SLE patients showed a moderate SC (70.2% versus 98.1%; P < 0.001) and moderate frequency of NAb positivity (61.5% versus 84.6%; P = 0.002), although both frequencies were lower than in controls. Factors associated with lower SC in univariate analysis at D69 were prednisone use (odds ratio [OR] 0.215 [95% confidence interval (95% CI) 0.108-0.427], P < 0.001) and mycophenolate mofetil (MMF) use (OR 0.201 [95% CI 0.107-0.378], P < 0.001), whereas hydroxychloroquine (HCQ) use led to a 2.5 increase in SC (P = 0.011). SLE patients who were receiving HCQ monotherapy had similar SC to controls at D69 (100% versus 98.1%; P = 1.000). In multivariate analysis, prednisone and MMF use were independently associated with lower SC (P < 0.001) and NAb positivity (P < 0.001). Safety analysis revealed no moderate/severe adverse events., Conclusion: Sinovac-CoronaVac has a moderate immunogenicity in SARS-CoV-2-naive SLE patients with an excellent safety profile. We further demonstrate that HCQ may improve SC, whereas prednisone and MMF had a major deleterious effect in vaccine response, reinforcing the need to investigate the role of temporary MMF withdrawal or a vaccine-booster dose (ClinicalTrials.gov identifier: NCT04754698)., (© 2021 American College of Rheumatology.)

Background: We aimed to examine the immunogenicity pattern induced by the inactivated SARS-CoV-2 vaccine CoronaVac (Sinovac Life Sciences, Beijing, China) in SARS-CoV-2 seropositive patients with autoimmune rheumatic diseases compared with seropositive controls, seronegative patients with autoimmune rheumatic diseases, and seronegative controls., Methods: CoronavRheum is an ongoing, prospective, controlled, phase 4 study, in which patients aged 18 years or older with autoimmune rheumatic diseases, and healthy controls were recruited from a single site (Rheumatology Division of Hospital das Clínicas, Faculdade de Medicina da Universidade de São Paulo) in São Paulo, Brazil Participants were vaccinated with two doses of CoronaVac (intramuscular injection, 3 μg in 0·5 mL of β-propiolactone inactivated SARS-CoV-2) on day 0 and on day 28. Blood samples were taken pre-vaccination on day 0, day 28, and also on day 69. For this subgroup analysis, participants were defined as being SARS-CoV-2 seropositive or seronegative prevaccination via anti-SARS-CoV-2 spike (S)1 or S2 IgG (cutoff of 15·0 arbitrary units [AU] per mL) or neutralising antibody titres (cutoff of ≥30%) and were matched for age and sex, via convenience sampling, in a 1:3:1:1 ratio (seropositive patients to seronegative patients to seropositive controls to seronegative controls). The primary outcomes were rates of anti-SARS-CoV-2 S1 and S2 IgG seropositivity and SARS-CoV-2 neutralising antibody positivity at day 28 and day 69 and immunogenicity dynamics assessed by geometric mean titres (GMTs) of IgG and median neutralising activity in seropositive patients with autoimmune rheumatic diseases compared with seronegative patients and seropositive and seronegative controls. We assessed safety in all participants randomly selected for this subgroup analysis. This study is registered with ClinicalTrials.gov, NCT04754698, and is ongoing for long-term immunogenicity evaluation., Findings: Between Feb 4 and Feb 8, 2021, 1418 patients and 542 controls were recruited, of whom 1685 received two vaccinations (1193 patients and 492 controls). After random sampling, our immunogenicity analysis population comprised 942 participants, of whom 157 were SARS-CoV-2 seropositive patients with autoimmune rheumatic diseases, 157 were seropositive controls, 471 were seronegative patients, and 157 were seronegative controls; the median age was 48 years (IQR 38-56) and 594 (63%) were female and 348 (37%) were male. For seropositive patients and controls, an increase in anti-SARS-CoV-2 S1 and S2 IgG titres (seropositive patients GMT 52·3 [95% CI 42·9-63·9] at day 0 vs 128·9 [105·6-157·4] at day 28; seropositive controls 53·3 [45·4-62·5] at day 0 vs 202·0 [174·8-233·4] at day 28) and neutralising antibody activity (seropositive patients 59% [IQR 39-83] at day 0 vs 82% [54-96] at day 28; seropositive controls 58% [41-79] at day 0 vs 92% [79-96] at day 28), was observed from day 0 to day 28, without further increases from day 28 to day 69 (at day 69 seropositive patients' GMT was 137·1 [116·2-161·9] and neutralising antibody activity was 79% [57-94]); and seropositive controls' GMT was 188·6 [167·4-212·6] and neutralising antibody activity was 92% [75-96]). By contrast, for seronegative patients and controls, the second dose was required for maximum response at day 69, which was lower in seronegative patients than in seronegative controls. GMTs in seronegative patients were 2·3 (95% CI 2·2-2·3) at day 0, 5·7 (5·1-6·4) at day 28, and 29·6 (26·4-33·3) at day 69, and in seronegative controls were 2·3 (2·1-2·5) at day 0, 10·6 (8·7-13·1) at day 28, and 71·7 (63·5-81·0) at day 69; neutralising antibody activity in seronegative patients was 15% (IQR 15-15) on day 0, 15% (15-15) at day 28, and 39% (15-65) at day 69, and in seronegative controls was 15% (15-15) at day 0, 24% (15-37) at day 28, and 61% (37-79) at day 69. Neither seronegative patients nor seronegative controls reached the GMT or antibody activity levels of seropositive patients at day 69., Interpretation: By contrast with seronegative patients with autoimmune rheumatic diseases, seropositive patients have a robust response after a single dose of CoronaVac. Our findings raise the possibility that the reduced immunogenicity observed in seronegative patients might not be the optimum response potential to SARS-CoV-2 vaccination, and therefore emphasise the importance of at least a single booster vaccination in these patients., Funding: Fundação de Amparo à Pesquisa do Estado de São Paulo, Conselho Nacional de Desenvolvimento Científico e Tecnológico, and B3-Bolsa de Valores do Brasil., Translation: For the Portuguese translation of the abstract see Supplementary Materials section., Competing Interests: We declare no competing interests., (© 2021 Elsevier Ltd. All rights reserved.)

Objective: Low hydroxychloroquine (HCQ) blood levels are predictors of flare in adult lupus. Childhood-onset systemic lupus erythematosus (cSLE) has high morbidity with renal involvement in up to 80% of cases. The aim of this study is to determine the HCQ cut-off levels which predicts flare in childhood-onset lupus nephritis (LN)., Methods: Sixty LN patients on HCQ use for at least 6-months were prospectively evaluated at baseline (BL) and about 6-months later for cSLE flare and HCQ blood levels (ng/mL) measured by liquid chromatography-tandem mass spectrometry., Results: There were 19 patients (32%) with flare, during the study with median SLEDAI increase of 4 (0-8). Median (IQR) BL HCQ levels of the flare group were lower compared to stable patients [557.5 (68.6-980.3) vs. 1061.9 (534.8-1590.0 ng/mL); p =0.012]. ROC curve analysis demonstrated that HCQ levels≤1075 ng/mL were associated with a 5.08 (95%CI 1.28-20.13; p =0.021) times increased risk of flare. Six-month HCQ levels revealed that most patients 24/54 (44%) had persistently low levels (≤1075) during follow-up. Among those, 11/24 (46%) had flare. Multiple logistic regression analysis including prednisone use, baseline SLEDAI-2K, adherence based on pharmacy refill and BL HCQ blood levels as possible predictors of flare revealed that only HCQ blood level was independently associated with flare (OR 0.999, 95%CI 0.998-1.0, p =0.013)., Conclusions: We demonstrated that HCQ blood cut-off level under 1075 ng/mL predicts flare in childhood-onset LN patients under prescribed HCQ dose of 4.0-5.5 mg/kg/day. We further observed that most of these patients have compliance issues reinforcing the need for a close surveillance particularly in those with levels below the defined cut-off.