Frederica Dedo Partey

Background: Durability and breadth of SARS-CoV-2-specific T-cell responses following booster vaccination remain key to guiding next-generation vaccine design, especially in the context of waning antibodies, emerging variants, and diverse immunological backgrounds. This longitudinal study assessed IFN-γ-producing T-cell responses in 46 fully vaccinated adults who received a booster dose of either the BNT162b2 (mRNA) or Ad26.COV2.S (adenoviral vector) vaccine. All participants were nucleocapsid-seropositive at baseline, with antibody levels stable throughout follow-up, indicating prior natural infection and no incident infection during the study period. Methods: Using an ex vivo IFN-γ ELISpot assay, responses were measured at four timepoints (baseline, Months 3, 6 and 9) against spike (S; n = 46) and nucleocapsid (N; n = 16) peptides selected by NetMHCpan-4.1 prediction from overlapping 15-mer libraries spanning both proteins. Each peptide was tested individually, allowing every response to be assigned to a defined sequence. Longitudinal change was modelled using linear mixed-effects models, comparing total with median per-peptide responses to distinguish loss of specificities from loss of per-epitope strength. Analyses were stratified by booster type and vaccination strategy (homologous vs. heterologous). Results: Time strongly affected total S-specific IFN-γ responses (F(3, 96.6) = 33.16, p = 8 × 10 ⁻¹⁵ ) but not median per-peptide responses (F(3, 95.8) = 0.62, p = 0.606), indicating that the decline reflected contraction in the number of epitopes recognized rather than weakening of individual responses; the same dissociation held within both booster groups. Ad26.COV2.S boosting was associated with broader S-specific epitope recognition and greater durability, with a subset of responses persisting through Month 9, whereas BNT162b2 recipients showed higher cumulative IFN-γ magnitude through Month 6 — a difference already present before boosting (p = 0.012). N-specific responses declined despite stable anti-nucleocapsid antibody, although two N-derived regions (YGANKDGIIW, VTPSGTWLTY) were recognized at every timepoint. Discussion/conclusions: Booster platform and vaccination strategy shaped the magnitude, breadth and durability of SARS-CoV-2-specific T-cell responses, with the longitudinal decline appearing to be driven predominantly by narrowing of epitope breadth among Month 3-reactive peptides rather than reduced per-epitope function. The persistently immunogenic S and N epitopes identified here warrant further evaluation as candidates for multi-epitope T-cell vaccine design.

Background/objectives: SARS-CoV-2 antibodies wane after natural infections and vaccinations. COVID-19 booster vaccination enhances the durability and functionality of antibodies against emerging SARS-CoV-2 variants. Data on booster-induced antibody durability in sub-Saharan Africa remain sparse. Comparative analysis of vaccine-induced responses between heterologous and homologous vaccination regimens remains limited. This study evaluated longitudinal RBD-specific IgG responses following homologous and heterologous COVID-19 booster vaccination in previously vaccinated adults. Methods: Adults with prior mRNA or adenoviral-vectored vaccination were boosted with either Pfizer (mRNA) or Janssen (adenoviral-vectored) vaccines. Plasma IgG binding to Wuhan, Delta, and Omicron RBDs was measured pre-booster and at 3, 6, and 9 months. A total of 181 participants were enrolled between November 2022 and October 2023. Results: More than 60% of participants had detectable pre-booster RBD- and N-antigen-specific IgG. Booster vaccination substantially increased Wuhan-specific RBD-IgG at three months, with limited boosting of Delta and Omicron responses. Antibody levels waned to pre-booster concentrations by month nine. Heterologous boosting with a viral-vectored prime followed by Pfizer mRNA significantly enhanced both peak RBD-IgG levels and durability. Conclusions: These longitudinal data provide rare real-world evidence on booster immunogenicity in African adults and demonstrate that heterologous regimens confer a short- to intermediate-term advantage in antibody magnitude compared to a homologous regimen. This benefit was most pronounced within the first six months post-boost. The findings support additional booster dosing to strengthen protection against emerging variants in sub-Saharan Africa.

COVID-19 booster vaccinations are needed to enhance waning immunity and the emergence of new variants. In Africa, where COVID-19 vaccine coverage is low, there is a paucity of data on COVID-19 vaccine-induced immunity, particularly in the post-omicron era. This study examined the functional activity of vaccine-induced antibody responses against different variants before and after booster vaccinations in adults in Ghana, between November 2022 and February 2023. SARS-CoV-2 nucleocapsid protein and spike receptor binding domain (RBD) antigen-specific IgG levels against different viral variants were determined in plasma. Plasma was tested for the ability to inhibit ACE-2 binding to RBD variants. N antigen-specific antibody levels were comparable between vaccinated and previously infected, but unvaccinated individuals. However, RBD IgG levels before booster vaccinations were significantly higher in vaccinated participants than in exposed, unvaccinated individuals, except for Omicron. RBD IgG levels remained unchanged after the booster in participants with three prior vaccine doses but were significantly higher than in those with only primary vaccinations (Wild type p = 0.0315, Alpha p = 0.0090, Beta p = 0.0020, Delta p = 0.0040) except Omicron (p = 0.09). Participants who received the Pfizer-BioNTech vaccine showed a significant increase (p < 0.05) in RBD IgG levels against all tested variants from baseline to 3 months. In contrast, participants who received the J&J vaccine only showed a significant increase in RBD IgG to Wildtype (p = 0.04), Alpha (p < 0.0001), and Beta (p < 0.0001), but not Delta and Omicron. The inhibition of ACE-2 binding and live virus neutralization titers were significantly higher in vaccinated individuals than in unvaccinated individuals before the booster (p < 0.001). Virus neutralization titers against Wildtype were significantly high 3 months after booster (p < 0.001), but neutralization titers against Omicron remained stable from baseline to 3 months after booster. Extended interval between vaccinations may enhance vaccine-induced antibody responses.

Malaria, caused by Plasmodium parasites, remains life-threatening, with Plasmodium falciparum responsible for severe cases. The parasite’s invasion of Red Blood Cells (RBCs) is critical for infection. The interaction between Reticulocyte Binding Protein Homologue 5 (RH5), Basigin, monoclonal antibodies and Cysteine-Rich Protective Antigen (CyRPA) with glycan on RBCs is essential for this process. This study aims to identify small molecules inhibiting the RH5-CyRPA-RIPr invasion complex. A library of 2299 compounds from FDA-approved drugs and African natural products in the ZINC database was screened using molecular docking. Binding sites for Basigin, monoclonal antibodies and glycans on RH5 and CyRPA were targeted, with binding affinity cutoffs of −8.5 kcal/mol for monoclonal antibodies and −7.0 kcal/mol for CyRPA and Basigin. Compounds were assessed for pharmacokinetics, solubility, drug-likeness, lead-likeness and biological activity using the PASS online server. Molecular dynamics simulations and free energy calculations evaluated stability and binding efficiency. Nine hits for RH5 and three for CyRPA showed favorable stability and anti-protozoal activity (up to 0.65). African natural products exhibited similarities with drugs like Nequinate and Cyanidin, supporting further research. Promising small molecules were identified as potential inhibitors of P. falciparum invasion, laying a foundation for experimental validation and drug development.

Clinical immunity to malaria develops slowly after repeated episodes of infection and antibodies are essential in naturally acquired immunity against malaria. However, chronic exposure to malaria has been linked to perturbation in B-cell homeostasis with the accumulation of atypical memory B cells. It is unclear how perturbations in B cell subsets influence antibody breadth, avidity, and function in individuals naturally exposed to malaria. We show that individuals living in high malaria transmission regions in Ghana have higher Plasmodium falciparum merozoite antigen-specific antibodies and an increased antibody breadth score but lower antibody avidities relative to low transmission regions. The frequency of circulating atypical memory B cells is positively associated with an individual's antibody breadth. In vitro growth inhibition is independent of the ability to bind to free merozoites but associated with the breadth of antibody reactivity in an individual. Taken together, our data shows that repeated malaria episodes hamper the development of high avid antibodies which is compensated for by an increase in antibody breadth. Our results provide evidence to reinforce the idea that in regions with high malaria prevalence, repeated malaria infections lead to the broadening of antibody diversity and the continued presence of atypical memory B cell populations.

P. falciparum causes the most severe form of malaria in younger children and pregnant women. In vitro culture systems allow researchers to understand parasite biology, elucidate mechanism of host immunity and test efficacy of antimalarial agents or vaccines in preclinical studies. Most laboratory-adapted parasite strains predate the emergence of artemisinin-based drug combinations and mainly originate from Asia or Europe. To fully understand the biochemical and phenotypic characteristics of parasites, it is imperative that researchers are able to culture parasites circulating in an area to unravel any geographical differences at the population level. Ex vivo culturing of clinical isolates can be challenging when collecting samples in the field and requires technical expertise and equipment. To overcome this challenge, clinical isolates are cryopreserved in the field and transported to a laboratory for in vitro studies. In this protocol, we describe different methods of cryopreserving P. falciparum isolates in the field and thawing them for subsequent in vitro culture. Key words P. falciparum Clinical isolate Cryopreservation Thawing parasites Field isolate Snap freezing Glycerolyte

Estimating malaria parasite density is important for patient care and management in rural and urban health centers in endemic areas. Here, we describe methodologically the protocols and methods to identify and enumerate Plasmodium falciparum parasites from infected blood using light microscopy. We provide step-by-step protocols and evaluate any possible drawbacks that may limit the methods and prospects of using light microscopy in diagnosing malaria. Key words Microscopy P. falciparum Diagnosis Parasitemia Giemsa stain

Following the coronavirus outbreaks described as severe acute respiratory syndrome (SARS) in 2003 and the Middle East respiratory syndrome (MERS) in 2012, the world has again been challenged by yet another corona virus, named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). SARS-CoV-2 infections were first detected in a Chinese Province in December 2019 and then declared a pandemic by the World Health Organization in March 2020. An infection caused by SARS-CoV-2 may result in asymptomatic, uncomplicated or fatal coronavirus disease 2019 (COVID-19). Fatal disease has been linked with the uncontrolled “cytokine storm” manifesting with complications mostly in people with underlying cardiovascular and pulmonary disease conditions. The severity of COVID-19 disease and the associated mortality has been disproportionately lower in terms of number of cases and deaths in Africa and also Asia in comparison to Europe and North America. Also, persons of colour residing in Europe and North America have been identified as a highly susceptible population due to a combination of several socioeconomic factors and poor access to quality healthcare. Interestingly, this has not been the case in sub-Saharan Africa where majority of the population are even more deprived of the aforementioned factors. On the contrary, sub-Saharan Africa has recorded the lowest levels of mortality and morbidity associated with the disease, and an overwhelming proportion of infections are asymptomatic. Whilst it can be argued that these lower number of cases in Africa may be due to challenges associated with the diagnosis of the disease such as lack of trained personnel and infrastructure, the number of persons who get infected and develop symptoms is proportionally lower than those who are asymptomatic, including asymptomatic cases that are never diagnosed. This review discusses the most probable reasons for the significantly fewer cases of severe COVID-19 disease and deaths in sub-Saharan Africa.

Following the coronavirus outbreaks described as severe acute respiratory syndrome (SARS) in 2003 and the Middle East respiratory syndrome (MERS) in 2012, the world has again been challenged by yet another corona virus, named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). SARS-CoV-2 infections were first detected in a Chinese Province in December 2019 and then declared a pandemic by the World Health Organization in March 2020. An infection caused by SARS-CoV-2 may result in asymptomatic, uncomplicated or fatal coronavirus disease 2019 (COVID-19). Fatal disease has been linked with the uncontrolled “cytokine storm” manifesting with complications mostly in people with underlying cardiovascular and pulmonary disease conditions. The severity of COVID-19 disease and the associated mortality has been disproportionately lower in terms of number of cases and deaths in Africa and also Asia in comparison to Europe and North America. Also, persons of colour residing in Europe and North America have been identified as a highly susceptible population due to a combination of several socioeconomic factors and poor access to quality healthcare. Interestingly, this has not been the case in sub-Saharan Africa where majority of the population are even more deprived of the aforementioned factors. On the contrary, sub-Saharan Africa has recorded the lowest levels of mortality and morbidity associated with the disease, and an overwhelming proportion of infections are asymptomatic. Whilst it can be argued that these lower number of cases in Africa may be due to challenges associated with the diagnosis of the disease such as lack of trained personnel and infrastructure, the number of persons who get infected and develop symptoms is proportionally lower than those who are asymptomatic, including asymptomatic cases that are never diagnosed. This review discusses the most probable reasons for the significantly fewer cases of severe COVID-19 disease and deaths in sub-Saharan Africa.

Following the coronavirus outbreaks described as severe acute respiratory syndrome (SARS) in 2003 and the Middle East respiratory syndrome (MERS) in 2012, the world has again been challenged by yet another corona virus, named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). SARS-CoV-2 infections were first detected in a Chinese Province in December 2019 and then declared a pandemic by the World Health Organization in March 2020. An infection caused by SARS-CoV-2 may result in asymptomatic, uncomplicated or fatal coronavirus disease 2019 (COVID-19). Fatal disease has been linked with the uncontrolled “cytokine storm” manifesting with complications mostly in people with underlying cardiovascular and pulmonary disease conditions. The severity of COVID-19 disease and the associated mortality has been disproportionately lower in Africa and Asia in comparison to Europe and North America in terms of number of cases and deaths. While persons of colour who live in Europe and North America have been identified as a highly susceptible population due to a combination of several socioeconomic factors and poor access to quality healthcare, this has not been the case in sub-Saharan Africa where inhabitants are even more deprived concerning the said factors. On the contrary, sub-Saharan Africa has recorded the lowest levels of mortality and morbidity associated with the disease, and an overwhelming proportion of infections are asymptomatic. This review discusses the most probable reasons for the significantly fewer cases of severe COVID-19 disease and deaths in sub-Saharan Africa.