SummaryEpidemiological research studies into Long Covid, currently defined by prolonged symptoms after SARS-CoV-2 infection, have reported widely varying prevalence estimates. As well as rapidly evolving scientific knowledge of Long Covid, these differences are partly driven by substantial methodological heterogeneity between studies, including the outcome definition of Long Covid; duration of follow-up; study design, period and population; sampling frame; data source; and the statistical techniques employed. Having a robust understanding of the prevalence of and risk factors for Long Covid is essential for informing treatment pathways, service provision and policy decisions. In preparation for the public health response to future epidemics and pandemics, this review outlines key epidemiological and statistical considerations and recommendations when designing studies of emerging post-acute infection syndromes, focussing on Long Covid as a case study.

SummaryBackgroundThere is a lack of summarized information regarding the uptake of pre-exposure prophylaxis (PrEP) among HIV negative gay, bisexual and other men who have sex with men (GBMSM) who engage in chemsex. This systematic review and meta-analysis aimed to summarize, assess the quality of existing evidence, estimate the prevalence of PrEP uptake among GBMSM who engage in chemsex, based on available global evidence; and evaluate whether engagement in chemsex is associated with increased odds of PrEP uptake in this population.MethodsWe searched Medline, Embase, Cochrane Reviews and CENTRAL, APA PsycInfo, Scopus, and LILACS. We included studies reporting chemsex practices among adult cisgender GBMSM and PrEP uptake until July 1, 2025. Evidence quality was assessed using the Newcastle–Ottawa Scale tool. Chemsex exposure was analyzed using two timeframe groups: recent (past 6 months) and ever (any longer or unspecified timeframe). Prevalence and associations -odds ratio (OR)- were pooled in meta-analyses using a random-effect model. Inconsistency, sensitivity, and publication bias analyses were conducted. PROSPERO registration: CRD42024573871.FindingsAmong 3988 records screened, 28 studies comprising 36,339 participants across three world regions were included: Western and Central Europe and North America, Asia and the Pacific, and Latin America; all were rated low to moderate quality. The overall prevalence of PrEP use was 39% (95% CI: 29–49%) among GBMSM who engaged in chemsex, with no significant differences between recent and ever chemsex timeframe groups. Sensitivity analyses and meta-regressions showed no significant effect of study publication year, country income group or world region. Overall chemsex was associated with higher odds of PrEP use (OR = 3.44, 95% CI: 2.70–4.38), with a significantly stronger association for ever chemsex (OR = 4.74, 95% CI: 3.48–6.46) than for recent chemsex (OR = 2.84, 95% CI: 2.11–3.81p < 0.05). Meta-regressions indicated significantly lower odds of PrEP use in studies from low- and middle-income countries for both recent (OR = 0.54, 95% CI: 0.31–0.94; p = 0.031) and ever (OR = 0.46, 95% CI: 0.21–0.99; p = 0.046) chemsex timeframes. Heterogeneity remained moderate to high across all analyses.InterpretationOur findings suggest that PrEP use is relatively common among GBMSM who engage in chemsex globally and chemsex is consistently and strongly associated with increased PrEP uptake in this population. The association between chemsex and PrEP use was significantly higher in studies from high-income settings, where chemsex practices are better described and PrEP is more widely available for this group. The lack of standardized definitions in the field contributes to the high heterogeneity and strongly influences the generation of global evidence. This first systematic review and metanalysis in the field highlights the need to expand and integrate chemsex harm reduction and PrEP services for GBMSM, especially in low- and middle-income settings, to improve health outcomes and advance towards the global HIV elimination goals.FundingPublication fees were sponsored by the Research Group of the HIV Unit, Infectious Disease Division, Department of Medicine, Geneva University Hospitals, Geneva, Switzerland. The Covidence membership and the fees for an academic librarian developing a professional systematic search strategy were sponsored by the Research Group of the HIV Unit, Infectious Diseases Service, Hospital Clinic, and IDIBAPS, University of Barcelona, Barcelona, Spain. No further funding was received for this study.

SummaryBackgroundGlucagon-like peptide 1 receptor agonists (GLP-1RAs) have emerged as breakthrough agents for weight loss. However, discontinuation is common, and clinical trials have demonstrated significant weight regain following cessation. In this systematic review, we aimed to characterise the trajectory of weight regain after GLP-1RA cessation.MethodsThis systematic review and meta-regression analysis followed Cochrane and PRISMA guidelines. We searched MEDLINE, Embase, Cochrane Library, Scopus and Web of Science from inception to August 28, 2025 for randomised controlled trials (RCTs), non-randomised interventional studies and observational studies reporting weight outcomes after cessation of GLP-1RAs in adults with overweight or obesity. Weight regain was the primary outcome and was modelled using nonlinear regression. Secondary, exploratory outcomes included HbA1c and systolic blood pressure. The study protocol is registered with PROSPERO (CRD420250631751).FindingsA total of 48 relevant studies were included. Weight consistently rebounded after cessation of GLP-1RAs. Six RCTs with 3236 participants were included in the nonlinear meta-regression, which utilised a mixed-effect exponential recovery model with random effects applied to the rate constant. At 1 year post-cessation, 60% of the weight lost during treatment was regained. Beyond 52 weeks, weight trajectories were extrapolated, with weight regain estimated to plateau at 75.3% (95% CI 68.9–81.6) of the weight lost on treatment. The rate constant was 0.0302 per week (95% CI 0.0202–0.0401), corresponding to a half-life of 23.0 weeks (95% CI 17.3–34.3). Most studies were assessed to have a moderate risk of bias.InterpretationGLP-1RA cessation is associated with a predictable and decelerating pattern of weight regain, which appears to plateau below pre-treatment levels, suggesting that partial weight-loss benefit may persist long-term but is substantially attenuated.FundingNone.