Many countries in sub-Saharan Africa have experienced lower COVID-19 caseloads and fewer deaths than countries in other regions worldwide. Under-reporting of cases and a younger population could partly account for these differences, but pre-existing immunity to coronaviruses is another potential factor. Blood samples from Sierra Leonean Lassa fever and Ebola survivors and their contacts collected before the first reported COVID-19 cases were assessed using enzyme-linked immunosorbent assays for the presence of antibodies binding to proteins of coronaviruses that infect humans. Results were compared to COVID-19 subjects and healthy blood donors from the United States. Prior to the pandemic, Sierra Leoneans had more frequent exposures than Americans to coronaviruses with epitopes that cross-react with severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), SARS-CoV, and Middle Eastern respiratory syndrome coronavirus (MERS-CoV). The percentage of Sierra Leoneans with antibodies reacting to seasonal coronaviruses was also higher than for American blood donors. Serological responses to coronaviruses by Sierra Leoneans did not differ by age or sex. Approximately a quarter of Sierra Leonian pre-pandemic blood samples had neutralizing antibodies against SARS-CoV-2 pseudovirus, while about a third neutralized MERS-CoV pseudovirus. Prior exposures to coronaviruses that induce cross-protective immunity may contribute to reduced COVID-19 cases and deaths in Sierra Leone.

Non-typhoidal salmonellosis, caused by Salmonella enterica serovar Typhimurium is a common fecal-oral disease characterized by mild gastrointestinal distress resulting in diarrhea, chills, fever, abdominal cramps, head and body aches, nausea, and vomiting. Increasing incidences of antibiotic resistant invasive non-typhoidal Salmonella infections makes this a global threat requiring novel treatment strategies including next-generation vaccines. The goal of the current study was to formulate a novel vaccine platform against Salmonella infection that could be delivered orally. To accomplish this, we created a Salmonella-specific vaccine adjuvanted with Burkholderia pseudomallei outer membrane vesicles (OMVs). We show that adding OMVs to a heat-killed oral Salmonella vaccine (HKST + OMVs) protects against a lethal, oral challenge with Salmonella. Further, we show that opsonizing anti-Salmonella antibodies are induced in response to immunization and that CD4 T cells and B cells can be induced when OMVs are used as the oral adjuvant. This study represents a novel oral vaccine approach to combatting the increasing problem of invasive Salmonella infections.

Serological assays are essential for infectious disease surveillance and vaccine evaluation because they detect antibody responses that persist beyond the period of active viral replication. The reliability of these assays, however, depends heavily on the structural and functional stability of the antigens used. Recombinant proteins—such as the SARS‑CoV‑2 Spike—are vulnerable to degradation from suboptimal handling, storage, and repeated freeze–thaw cycles, which can compromise assay performance. To address this concern, we systematically assessed the impact of three commonly used aliquoting and freezing approaches on the long‑term stability of a recombinant SARS‑CoV‑2 Spike protein: (1) aliquoting on wet ice followed by storage at −80 °C, (2) aliquoting on dry ice followed by storage at −80 °C, and (3) aliquoting on dry ice followed by snap‑freezing in a methanol–dry ice bath. Aliquots from two manufacturing lots were evaluated over six months using multiple quality metrics, including purity, structural integrity [Analytical Size Exclusion Chromatography (AnSEC) and Thermal Shift Assay (TSA)], and functional performance in a validated IgG ELISA. Across all conditions and time points, antigen purity remained within the ideal A260/A280 range (0.6–0.8), with minimal nucleic acid contamination. ELISA performance demonstrated consistently low background and high sensitivity, specificity, and precision. Structural analyses confirmed stable protein size and conformation (AnSEC elution peaks within ±1.0 mL of baseline) and unchanged thermal stability (Tm within ±2.0 °C). These findings indicate that all tested methodologies effectively preserved antigen integrity under controlled laboratory conditions, providing a foundation for standardized SOPs while acknowledging that real‑world variability may influence outcomes.