Tasnuva Ahmed

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.

Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) primarily targets respiratory mucosa, causing coronavirus disease 2019 (COVID-19). Susceptibility and severity of COVID-19 may be influenced by predisposing factors including blood groups. In this study, we investigated whether natural anti-carbohydrate antibodies provide innate protection against SARS-CoV-2 and influence disease severity.Methodology: We used samples (plasma and saliva) from a longitudinal cohort study in Bangladesh that enrolled 100 COVID-19 symptomatic and asymptomatic patients. We also enrolled 21 and 38 healthy controls during the pandemic period and pre-pandemic period, respectively. We phenotype ABO blood grouping from blood and determined Lewis and secretor status (H antigen) from the saliva samples. We quantified natural anti-carbohydrate antibodies (anti-A, anti-B, anti-Tn-Mono and anti-αGal IgG, IgA, and IgM) from plasma collected at enrollment. We also explored the trend of natural anti-carbohydrate antibodies until 3 months of convalescence period among the COVID-19 patients (day 14 and day 90 from enrollment). Antibody quantification and ABH/Lewis phenotyping were performed using enzyme-linked immunosorbent assay (ELISA).Results: We included 99 COVID-19 patients and 59 healthy controls assessing the differences of natural antibody titer during enrollment, while 95 patients were analyzed exploring Lewis and secretor status with natural antibody titer and disease status. We did not find significant difference in the distribution for neither ABO blood groups nor non-secretors and Lewis-negative individuals among asymptomatic or symptomatic patients and healthy controls. Nonetheless, we observed lower anti-A antibody titers among symptomatic patients compared to healthy controls. We also identified slight differences in antibody titers linked to age and gender. Anti-A and anti-B antibodies among asymptomatic patients had a higher trend up to 3 months from infection compared to symptomatic patients.Conclusion: Higher natural anti-A and anti-B antibody titers may offer protection against symptomatic COVID-19 infections. Gender and blood group differences indicate potential innate immune factors influencing disease severity, but larger studies are needed to confirm these findings.

Background: Typhoid fever, or enteric fever, is a highly fatal infectious disease that affects over 9 million people worldwide each year, resulting in more than 110,000 deaths. Reduction in the burden of typhoid in low-income countries is crucial for public health and requires the implementation of feasible water, sanitation, and hygiene (WASH) interventions, especially in densely populated urban slums. Objective: In this study, conducted in Mirpur, Bangladesh, we aimed to assess the association between household WASH status and typhoid risk in a training subpopulation of a large prospective cohort (n=98,087), and to evaluate the performance of a machine learning algorithm in creating a composite WASH variable. Further, we investigated the protection associated with living in households with improved WASH facilities and in clusters with increasing prevalence of such facilities during a 2-year follow-up period. Methods: We used a machine learning algorithm to create a dichotomous composite variable (“Better” and “Not Better”) based on 3 WASH variables: private toilet facility, safe drinking water source, and presence of water filter. The algorithm was trained using data from the training subpopulation and then validated in a distinct subpopulation (n=65,286) to assess its sensitivity and specificity. Cox regression models were used to evaluate the protective effect of living in “Better” WASH households and in clusters with increasing levels of “Better” WASH prevalence. Results: We found that residence in households with improved WASH facilities was associated with a 38% reduction in typhoid risk (adjusted hazard ratio=0.62, 95% CI 0.49-0.78; P<.001). This reduction was particularly pronounced in individuals younger than 10 years at the first census participation, with an adjusted hazard ratio of 0.49 (95% CI 0.36-0.66; P<.001). Furthermore, we observed an inverse relationship between the prevalence of “Better” WASH facilities in clusters and the incidence of typhoid, although this association was not statistically significant in the multivariable model. Specifically, the adjusted hazard of typhoid decreased by 0.996 (95% CI 0.986-1.006) for each percent increase in the prevalence of “Better” WASH in the cluster (P=.39). Conclusions: Our findings demonstrate that existing variations in household WASH are associated with differences in the risk of typhoid in densely populated urban slums. This suggests that attainable improvements in WASH facilities can contribute to enhanced typhoid control, especially in settings where major infrastructural improvements are challenging. These findings underscore the importance of implementing and promoting comprehensive WASH interventions in low-income countries as a means to reduce the burden of typhoid and improve public health outcomes in vulnerable populations.