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Vaccines are one of the greatest public health achievements and have saved millions of lives. They represent a key countermeasure to limit epidemics caused by emerging infectious diseases. The Ebola virus disease crisis in West Africa dramatically revealed the need for a rapid and strategic development of vaccines to effectively control outbreaks. Seven years later, in light of the SARS-CoV-2 pandemic, this need has never been as urgent as it is today. Vaccine development and implementation of clinical trials have been greatly accelerated, but still lack strategic design and evaluation. Responses to vaccination can vary widely across individuals based on factors like age, microbiome, co-morbidities and sex. The latter aspect has received more and more attention in recent years and a growing body of data provide evidence that sex-specific effects may lead to different outcomes of vaccine safety and efficacy. As these differences might have a significant impact on the resulting optimal vaccine regimen, sex-based differences should already be considered and investigated in pre-clinical and clinical trials. In this Review, we will highlight the clinical observations of sex-specific differences in response to vaccination, delineate sex differences in immune mechanisms, and will discuss the possible resulting implications for development of vaccine candidates against emerging infections. As multiple vaccine candidates against COVID-19 that target the same antigen are tested, vaccine development may undergo a decisive change, since we now have the opportunity to better understand mechanisms that influence vaccine-induced reactogenicity and effectiveness of different vaccines.

Recombinant vesicular stomatitis virus–Zaire Ebola virus (rVSV-ZEBOV) is the most advanced Ebola virus vaccine candidate and is currently being used to combat the outbreak of Ebola virus disease (EVD) in the Democratic Republic of the Congo (DRC). Here we examine the humoral immune response in a subset of human volunteers enrolled in a phase 1 rVSV-ZEBOV vaccination trial by performing comprehensive single B cell and electron microscopy structure analyses. Four studied vaccinees show polyclonal, yet reproducible and convergent B cell responses with shared sequence characteristics. EBOV-targeting antibodies cross-react with other Ebolavirus species, and detailed epitope mapping revealed overlapping target epitopes with antibodies isolated from EVD survivors. Moreover, in all vaccinees, we detected highly potent EBOV-neutralizing antibodies with activities comparable or superior to the monoclonal antibodies currently used in clinical trials. These include antibodies combining the IGHV3–15/IGLV1–40 immunoglobulin gene segments that were identified in all investigated individuals. Our findings will help to evaluate and direct current and future vaccination strategies and offer opportunities for novel EVD therapies.

A relief worker who became infected with the Ebola virus while working in Sierra Leone during the largest recorded Ebola epidemic was evacuated to Hamburg, Germany, for care. The details of his severe illness and response to supportive care are reported. Since December 2013, a Zaire ebolavirus (EBOV) epidemic of unprecedented scale has ravaged West Africa, with a focus on Guinea, Sierra Leone, and Liberia. 1 – 4 The current epidemic has led to a public health emergency in the region, exacerbated by high rates of infection among health care personnel. A substantial number of fatal cases are among health care workers. 2 Several international health care workers have been evacuated to specialized centers in Europe and the United States. The patient transferred to our isolation unit worked for the World Health Organization (WHO) as an epidemiologist in Sierra Leone and was airlifted at . . .

Neonatal mortality remains high in many low- and middle-income countries (LMICs), with neonatal sepsis and antimicrobial resistance (AMR) posing significant threats to newborns, particularly in sub-Saharan Africa (SSA). Tanzania is among the countries with the highest neonatal mortality rates, with sepsis being a major contributor. Gut dysbiosis has been identified as a risk factor for neonatal sepsis in high-income countries, due to factors like abundance of pathogenic bacteria, decrease in microbiome diversity, intestinal barrier defects and bacterial translocation. Understanding gut dysbiosis in the local setting and its role in sepsis development may offer new prevention strategies, such as probiotics for high-risk preterm infants. This prospective neonatal cohort, established at Muhimbili National Hospital (MNH) in Dar es Salaam, Tanzania, aims to analyze the gut microbiome of preterm infants and explore associations with neonatal late-onset sepsis (LOS). Additionally, data on bacterial pathogens of bloodstream infections and AMR prevalence will be identified. Secondary endpoints include clinical LOS, sepsis-related death, death from any cause, and hospital discharge outcomes. Eligible preterm neonates (28 + 0 to <34 weeks of gestational age, birth weight ≥ 1000g) will be recruited with maternal consent. Socio-demographic and clinical data, microbiological details of blood pathogens, and a set of fresh frozen fecal samples during the 28 days observation period will be collected. The study targets a sample size of 1350 participants and we expect 72-135 culture-proven LOS during a study period of 18 months. Fecal samples will undergo next-generation sequencing (NGS) to analyze microbial community functions in comparison to matched controls. This collaborative study between universities in Tanzania and Germany, aims to analyze the neonatal microbiome in relation to sepsis development and AMR of blood culture isolates to enhance neonatal sepsis care, improve diagnostics and treatment. The project will offer insights into potential therapeutic strategies for the future, promote academic exchange, capacity building and research on African microbiomes.

Beginning in May 2022, a rising number of monkeypox cases were reported in non-monkeypox-endemic countries in the Northern Hemisphere. We adapted 2 published quantitative PCRs for use as a dual-target monkeypox virus test on widely used automated high-throughput PCR systems. We determined analytic performance by serial dilutions of monkeypox virus reference material, which we quantified by digital PCR. We found the lower limit of detection for the combined assays was 4.795 (95% CI 3.6-8.6) copies/mL. We compared clinical performance against a commercial manual orthopoxvirus research use only PCR kit by using clinical remnant swab samples. Our assay showed 100% positive (n = 11) and 100% negative (n = 56) agreement. Timely and scalable PCR tests are crucial for limiting further spread of monkeypox. The assay we provide streamlines high-throughput molecular testing for monkeypox virus on existing broadly established platforms used for SARS-CoV-2 diagnostic testing.

Background. Spontaneous control of human immunodeficiency virus (HIV) infection has been documented in a minority of HIV-infected individuals. The mechanisms behind this outcome remain largely unknown, and a better understanding of them will likely influence future vaccine strategies. Methods. HIV-specific T cell and antibody responses as well as host genetics were examined in untreated HIVinfected patients who maintain comparatively low plasma HIV RNA levels (hereafter, controllers), including those with levels of < 50 RNA copies/mL (elite controllers, n = 64), those with levels of 50–2000 copies/mL (viremic controllers, n = 60); we also examined HIV-specific T cell and antibody responses as well as host genetics for patients with levels of >10,000 copies/mL (chronic progressors, n = 30). Results. CD8+T cells from both controller groups preferentially target Gag over other proteins in the context of diverse HLA class I alleles, whereas responses are more broadly distributed in persons with progressive infection. Elite controllers represent a distinct group of individuals who have significantly more CD4 and CD8 T cells that secrete interferon-γ and interleukin-2 and lower levels of HIV-neutralizing antibodies. Individual responses were quite heterogeneous, and none of the parameters evaluated was uniquely associated with the ability to control viremia. Conclusions. Elite controllers are a distinct group, even when compared to persons with low level viremia, but they exhibit marked genetic and immunologic heterogeneity. Even low-level viremia among HIV controllers was associated with measurable T cell dysfunction, which has implications for current prophylactic vaccine strategies.

While several studies have described the clinical course of patients with coronavirus disease 2019 (COVID-19), direct comparisons with patients with seasonal influenza are scarce. We compared 166 patients with COVID-19 diagnosed between February 27 and June 14, 2020, and 255 patients with seasonal influenza diagnosed during the 2017–18 season at the same hospital to describe common features and differences in clinical characteristics and course of disease. Patients with COVID-19 were younger (median age [IQR], 59 [45–71] vs 66 [52–77]; P < 0001) and had fewer comorbidities at baseline with a lower mean overall age-adjusted Charlson Comorbidity Index (mean [SD], 3.0 [2.6] vs 4.0 [2.7]; P < 0.001) than patients with seasonal influenza. COVID-19 patients had a longer duration of hospitalization (mean [SD], 25.9 days [26.6 days] vs 17.2 days [21.0 days]; P = 0.002), a more frequent need for oxygen therapy (101 [60.8%] vs 103 [40.4%]; P < 0.001) and invasive ventilation (52 [31.3%] vs 32 [12.5%]; P < 0.001) and were more frequently admitted to the intensive care unit (70 [42.2%] vs 51 [20.0%]; P < 0.001) than seasonal influenza patients. Among immunocompromised patients, those in the COVID-19 group had a higher hospital mortality compared to those in the seasonal influenza group (13 [33.3%] vs 8 [11.6%], P = 0.01). In conclusion, we show that COVID-19 patients were younger and had fewer baseline comorbidities than seasonal influenza patients but were at increased risk for severe illness. The high mortality observed in immunocompromised COVID-19 patients emphasizes the importance of protecting these patient groups from SARS-CoV-2 infection.

Rabies pre-exposure prophylaxis (PrEP) is recommended to individuals at risk for exposure to rabies. Three intramuscular doses of the purified chick embryo cell (PCEC) rabies vaccine can be administered according to a conventional (four-week) or an accelerated (one-week) regimen. This phase III, open-label study (NCT02545517) was an extension of the NCT01662440 study where immune responses of different primary PrEP regimens with PCEC rabies vaccine and Japanese encephalitis (JE) vaccine were assessed. Adults who had completed the parent study and received three doses of rabies PrEP regimens, concomitantly with a JE vaccine or alone (i.e., Rabies+JE-Accelerated, Rabies+JE-Conventional, and Rabies-Conventional groups) were enrolled in this extension study. Here we evaluated the long-term (up to 10 years after completing the primary vaccination) immunogenicity and boostability of PCEC rabies vaccine, and the safety of booster dose(s). Immunogenicity was assessed in terms of rabies virus neutralizing antibody (RVNA) concentrations, and titers ≥0.5 international units (IU)/mL were considered adequate for protection. Participants with RVNA concentrations <0.5 IU/mL were eligible for receiving PCEC rabies vaccine booster(s). Of the 459 participants enrolled in this study, 77.6% completed the trial. At the study end, the probability of detecting adequate RVNA concentrations in unboosted participants was 57.8%, 60.2%, and 62.0% for the Rabies+JE-Accelerated, Rabies+JE-Conventional, and Rabies-Conventional groups, respectively. Overall, 68.6% of all participants had RVNA concentrations ≥0.5 IU/mL at any timepoint and did not require a booster dose during the study follow-up period. Of the 144 participants with RVNA concentrations <0.5 IU/mL at any timepoint, 132 needed one booster dose throughout the follow-up period (Years 3-10) and 12 needed multiple booster administrations. No safety concerns were identified. The PCEC rabies vaccine administered alone/concomitantly with the JE vaccine provides adequate immunity for up to 62% of unboosted participants at study end.

MVA-MERS-S, a vaccine candidate against Middle East respiratory syndrome (MERS), was recently evaluated in a randomized, placebo-controlled, double-blind phase 1b clinical trial to assess its safety, immunogenicity, and optimal dosing in healthy adults in Hamburg and Rotterdam. A three-dose regimen was safe and elicited robust spike-specific antibody responses. We extended this trial to assess the two-year durability of MERS-CoV-specific antibody and T cell responses in 48 study participants of the Hamburg cohort. Our findings show that immune responses remain detectable for at least 24 months after the third vaccination. Antibodies persisted at levels comparable to the peak response observed after the second vaccination and were able to cross-neutralize MERS-CoV spike mutants. Although the immune correlates of protection against MERS remain unknown, the observed durability of humoral and cellular immune responses supports the potential of MVA-MERS-S as a promising MERS vaccine candidate and highlights the importance of a booster dose in sustaining long-term immunity. This study assessed the durability of immunity in humans after vaccination with an MVA-based MERS vaccine. The data show that antibodies and T cells persist for at least two years, with the antibodies capable of cross-neutralizing MERS-CoV variants.

We are in the midst of a pandemic caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes the coronavirus disease 2019 (COVID-19). SARS-CoV-2 has caused more than two million deaths after one year of the pandemic. The world is experiencing a deep economic recession. Safe and effective vaccines are needed to prevent further morbidity and mortality. Vaccine candidates against COVID-19 have been developed at an unprecedented speed, with more than 200 vaccine candidates currently under investigation. Among those, 20 candidates have entered the clinical Phase 3 to evaluate efficacy, and three have been approved by the European Medicines Agency. The aim of immunization is to act against infection, disease and/or transmission. However, the measurement of vaccine efficacy is challenging, as efficacy trials need to include large cohorts with verum and placebo cohorts. In the future, this will be even more challenging as further vaccine candidates will receive approval, an increasing number of humans will receive vaccinations and incidence might decrease. To evaluate novel and second-generation vaccine candidates, randomized placebo-controlled trials might not be appropriate anymore. Correlates of protection (CoP) could be an important tool to evaluate novel vaccine candidates, but vaccine-induced CoP have not been clearly defined for SARS-CoV-2 vaccines. In this review, we report on immunogenicity against natural SARS-CoV-2 infection, vaccine-induced immune responses and discuss immunological markers that can be linked to protection. By discussing the immunogenicity and efficacy of forerunner vaccines, we aim to give a comprehensive overview of possible efficacy measures and CoP.