Bangladesh has experienced recurrent dengue outbreaks since 2000, driven by climatic changes and socio-demographic vulnerabilities. Limited evidence on circulating serotypes and immune diversity has hindered preparedness for severe dengue (SD). Identifying clinical and laboratory predictors of progression to severe dengue is key to strengthening outbreak response and clinical management. A longitudinal cohort study was conducted in four hospitals in Dhaka between January and November 2024. Patients with confirmed dengue with warning signs were enrolled. Clinical data and blood samples were collected at enrollment, clinical deterioration/discharge, and convalescence (day 21 ± 7). Multivariable logistic regression identified factors associated with SD compared with dengue with warning signs (DWS). Associations were expressed as odds ratios (OR) with 95% confidence intervals (CIs) and p-values < 0.05 considered y significant. Among 3135 dengue patients, 354 with warning signs were enrolled. 62 (17.5%) progressed to SD, including 2 deaths. Most of the patients (60%) were aged between 21 and 40 years, and 76% were male. Lethargy was more frequent in SD patients (29%) than DWS patients (11%). DEN-2 was the predominant serotype (90%). Multivariable logistic regression, adjusted for potential confounders, identified arthralgia (95% CI: 1.04–3.98), anorexia (95% CI: 1.40–11.7), lethargy (95% CI: 1.97–10.7), diabetes mellitus (95% CI: 1.01–6.17), pleural effusion (95% CI: 4.97–21.1) and prolonged APTT (95% CI: 1.02–1.08) as independent predictors for SD. The findings show that a few simple and easily measurable indicators can support early risk assessment and guide timely hospital admission and clinical management. 10.13039/100000200 United States Agency for International Development (USAID) under the Crisis Modifier Grant (GR-01909) in response to the dengue outbreak in Bangladesh.

Background: The dynamics of humoral immune responses following primary and booster COVID-19 vaccinations are crucial to understand in order to optimize vaccination strategies. This study evaluates the magnitude and durability of SARS-CoV-2-specific IgG antibody responses across different vaccines in a large cohort of Bangladeshi adults. Methods: A total of 6300 adults from nine hospitals across eight divisions of Bangladesh were enrolled. Participants received two primary doses of either ChAdOx1 nCoV-19 (Covishield, Serum Institute of India, n = 2855), mRNA-1273 (Moderna, n = 578), BNT162b2 (Pfizer-BioNTech, n = 121), or Vero-cell-inactivated (Sinopharm, n = 2746) vaccines. Booster doses were administered at one-year intervals post-primary vaccination. SARS-CoV-2 spike receptor-binding domain (RBD)-specific IgG antibody responses were measured by ELISA using serum from vaccinees at multiple time points after two primary and two booster doses. Results: A total of 3745 individuals received booster 1 (third dose), with 59% receiving heterologous boosters (a different vaccine regimen than the primary doses). Only 5.5% (n = 347) of participants received a second booster one year after the first booster (among them, 99% received BNT162b2). Our results suggest that heterologous boosters with the mRNA vaccine induced higher IgG levels than homologous boosters for individuals who received primary vaccination with adenovirus vector-based ChAdOx1 nCoV-19 or a Vero-cell-inactivated vaccine. However, in those who initially received the mRNA-based vaccine, both homologous and heterologous boosters produced comparable IgG responses. Among all vaccine types, booster immunization with the Vero-cell-inactivated vaccine induced the lowest antibody responses. Longitudinal analysis demonstrated significantly high IgG levels over the 12 months following the first booster (p < 0.0001); however, IgG levels declined significantly after the second booster dose (fourth dose). Conclusions: Heterologous boosting strategies, particularly those involving mRNA vaccines, elicit stronger and more sustained IgG responses compared to a homologous booster. However, antibody waning after the second booster highlights the need for continued monitoring and potential additional vaccine strategies.