Yellow fever vaccine

Sofosbuvir Off-label Treatment of Yellow Fever Patients During an Outbreak in Brazil, 2018: A Cohort Study

We enrolled 21 patients with laboratory-confirmed yellow fever (YF), hospitalized at Eduardo de Menezes Hospital, Brazil, to be treated with sofosbuvir, a drug approved for hepatitis C. Given the absence of specific YF antiviral treatments, the off-label nonrandomized sofosbuvir treatment aimed to address high disease severity and the risk of fatal outcomes. Patients received a daily dose of 400 mg sofosbuvir from 4 to 10 days post-symptom onset. YF viral load (VL) comparisons were made between treated and nontreated patients who either survived or died. The genomic VL for the treated group steadily decreased after day 7 post-symptom onset, suggesting that sofosbuvir might reduce YF VL. This study underscores the urgent need for YF antiviral therapies, advocating for randomized clinical trials to further explore sofosbuvir's role in YF treatment.

Yellow fever in Africa and the Americas: a historical and epidemiological perspective

Yellow fever was transported during the slave trade in the 15th and 16th centuries from Africa to the Americas where the virus encountered favorable ecological conditions that allowed creation of a sustainable sylvatic cycle. Despite effective vector control and immunization programs for nearly a century, yellow fever epidemics reemerged in many Latin American countries, particularly Brazil. The emergence or reemergence of vector-borne diseases encompasses many intricate factors. Yellow fever outbreaks occur if at least three conditions are fulfilled: the introduction of the virus into a non-immune human community, presence of competent and anthropophilic vectors and insufficiency of prevention and/or adequate management of the growing outbreak. On the other hand, two weapons are available to constrain yellow fever: vector control and immunization. In contrast, yellow fever is absent from Asia and the Pacific despite the presence of the vector and the susceptibility of human populations to the virus. Based on a review of the global history of yellow fever and its epidemiology, the authors deliver some recommendations for improving the prevention of epidemics.

Application of replication-defective West Nile virus vector to non-flavivirus vaccine targets

The RepliVax vaccine platform(RV) is based on flavivirus genomes that are rationally attenuated by deletion. The self-limiting infection provided by RV has been demonstrated to be safe, highly immunogenic and efficacious for several vaccine candidates against flaviviruses. Here respiratory syncytial virus (RSV) F, influenza virus HA, and simian immunodeficiency virus (SIV) Env proteins were expressed in place of either prM-E or C-prM-E gene deletions of the West Nile (WN) virus genome. The resulting RV-RSV, -influenza and -SIV vaccine prototypes replicated efficiently in complementing helper cells expressing the WN structural proteins in trans. Expressed antigens exhibited correct post-translational processing and the RV recombinants were shown to be highly attenuated and immunogenic in mice, eliciting strong antigen-specific antibodies as well as detectable T-cell responses. These data support the utility of RV vectors for development of vaccines against non-flavivirus targets including rabies and HIV.

A novel approach to a rabies vaccine based on a recombinant single-cycle flavivirus vector

The RepliVax® vaccine (RV) platform is based on flavivirus genomes that are rationally attenuated by deletion. These single-cycle RV vaccine candidates targeting flavivirus pathogens have been demonstrated to be safe, highly immunogenic, and efficacious in animal models, including non-human primates. Here we show utility of the technology for delivery of a non-flavivirus immunogen by engineering several West Nile-based RV vectors to express full-length rabies virus G protein. The rabies virus G protein gene was incorporated in place of different West Nile structural protein gene deletions. The resulting RV-RabG constructs were demonstrated to replicate to high titers (8 log₁₀ infectious particles/ml) in complementing helper cells. Following infection of normal cells, they provided efficient rabies virus G protein expression, but did not spread to surrounding cells. Expression of rabies virus G protein was stable and maintained through multiple rounds of in vitro passaging. A sensitive neurovirulence test in 2-3 day old neonatal mice demonstrated that RV-RabG candidates were completely avirulent indicative of high safety. We evaluated the RV-RabG variants in several animal models (mice, dogs, and pigs) and demonstrated that a single dose elicited high titers of rabies virus-neutralizing antibodies and protected animals from live rabies virus challenge (mice and dogs). Importantly, dogs were protected at both one and two years post-immunization, demonstrating durable protective immunity. The data demonstrates the potential of the RepliVax® technology as a potent vector delivery platform for developing vaccine candidates against non-flavivirus targets.

Antibody Responses to Zika Virus Infections in Environments of Flavivirus Endemicity

Zika virus (ZIKV) infections occur in areas where dengue virus (DENV), West Nile virus (WNV), yellow fever virus (YFV), and other viruses of the genus Flavivirus cocirculate. The envelope (E) proteins of these closely related flaviviruses induce specific long-term immunity, yet subsequent infections are associated with cross-reactive antibody responses that may enhance disease susceptibility and severity. To gain a better understanding of ZIKV infections against a background of similar viral diseases, we examined serological immune responses to ZIKV, WNV, DENV, and YFV infections of humans and nonhuman primates (NHPs). Using printed microarrays, we detected very specific antibody responses to primary infections with probes of recombinant E proteins from 15 species and lineages of flaviviruses pathogenic to humans, while high cross-reactivity between ZIKV and DENV was observed with 11 printed native viruses. Notably, antibodies from human primary ZIKV or secondary DENV infections that occurred in areas where flavivirus is endemic broadly recognized E proteins from many flaviviruses, especially DENV, indicating a strong influence of infection history on immune responses. A predictive algorithm was used to tentatively identify previous encounters with specific flaviviruses based on serum antibody interactions with the multispecies panel of E proteins. These results illustrate the potential impact of exposure to related viruses on the outcome of ZIKV infection and offer considerations for development of vaccines and diagnostics.

Biological challenges to effective vaccines in the developing world

The reason for holding a meeting to discuss biological challenges to vaccines is simple: not all vaccines work equally well in all settings. This special issue reviews the performance of vaccines in challenging environments, summarizes current thinking on the reasons why vaccines underperform and considers what approaches are necessary to understand the heterogeneity in responses and to improve vaccine immunogenicity and efficacy.

Immune activation alters cellular and humoral responses to yellow fever 17D vaccine

BACKGROUND

Defining the parameters that modulate vaccine responses in African populations will be imperative to design effective vaccines for protection against HIV, malaria, tuberculosis, and dengue virus infections. This study aimed to evaluate the contribution of the patient-specific immune microenvironment to the response to the licensed yellow fever vaccine 17D (YF-17D) in an African cohort.

METHODS

We compared responses to YF-17D in 50 volunteers in Entebbe, Uganda, and 50 volunteers in Lausanne, Switzerland. We measured the CD8+ T cell and B cell responses induced by YF-17D and correlated them with immune parameters analyzed by flow cytometry prior to vaccination.

RESULTS

We showed that YF-17D-induced CD8+ T cell and B cell responses were substantially lower in immunized individuals from Entebbe compared with immunized individuals from Lausanne. The impaired vaccine response in the Entebbe cohort associated with reduced YF-17D replication. Prior to vaccination, we observed higher frequencies of exhausted and activated NK cells, differentiated T and B cell subsets and proinflammatory monocytes, suggesting an activated immune microenvironment in the Entebbe volunteers. Interestingly, activation of CD8+ T cells and B cells as well as proinflammatory monocytes at baseline negatively correlated with YF-17D-neutralizing antibody titers after vaccination. Additionally, memory T and B cell responses in preimmunized volunteers exhibited reduced persistence in the Entebbe cohort but were boosted by a second vaccination.

CONCLUSION

Together, these results demonstrate that an activated immune microenvironment prior to vaccination impedes efficacy of the YF-17D vaccine in an African cohort and suggest that vaccine regimens may need to be boosted in African populations to achieve efficient immunity.

TRIAL REGISTRATION

Registration is not required for observational studies.

FUNDING

This study was funded by Canada's Global Health Research Initiative, Defense Threat Reduction Agency, National Institute of Allergy and Infectious Diseases, Bill & Melinda Gates Foundation, and United States Agency for International Development.

Yellow Fever outbreaks in unvaccinated populations, Brazil, 2008-2009

Due to the risk of severe vaccine-associated adverse events, yellow fever vaccination in Brazil is only recommended in areas considered at risk for disease. From September 2008 through June 2009, two outbreaks of yellow fever in previously unvaccinated populations resulted in 21 confirmed cases with 9 deaths (case-fatality, 43%) in the southern state of Rio Grande do Sul and 28 cases with 11 deaths (39%) in Sao Paulo state. Epizootic deaths of non-human primates were reported before and during the outbreak. Over 5.5 million doses of yellow fever vaccine were administered in the two most affected states. Vaccine-associated adverse events were associated with six deaths due to acute viscerotropic disease (0.8 deaths per million doses administered) and 45 cases of acute neurotropic disease (5.6 per million doses administered). Yellow fever vaccine recommendations were revised to include areas in Brazil previously not considered at risk for yellow fever.

Advances and controversies in yellow fever vaccination

Ever since its development in 1937, the live-attenuated 17D yellow fever (YF) vaccine has been one of the most effective vaccines available to man. In this review we highlight the major steps in the development of 17D YF vaccine. We discuss the use of neutralizing antibodies as a surrogate marker for protection, and explore the strengths and weaknesses of the current plaque reduction neutralization test (PRNT), a technique developed in the 1960s that continues to be superior to every modern test in both sensitivity and specificity. The neutralizing antibodies demonstrated by the PRNT can be detected for several decades after vaccination, possibly even for the remainder of the recipient's natural life. We review the available evidence on the duration of protection after primary vaccination, a topic that has been the subject of controversy over the last few months. For persons who are immunocompromised due to disease, medication or advancing age, the duration of protection may be shorter: they should always have their vaccine response checked by PRNT. Due to the higher risk of severe adverse events after vaccination with 17D YF in this group, the development of a new, inactivated vaccine will have substantial benefits in this population.

17DD yellow fever vaccine: a double blind, randomized clinical trial of immunogenicity and safety on a dose-response study

OBJECTIVE

To verify if the Bio-Manguinhos 17DD yellow fever vaccine (17DD-YFV) used in lower doses is as immunogenic and safe as the current formulation.

RESULTS

Doses from 27,476 IU to 587 IU induced similar seroconversion rates and neutralizing antibodies geometric mean titers (GMTs). Immunity of those who seroconverted to YF was maintained for 10 mo. Reactogenicity was low for all groups.

METHODS

Young and healthy adult males (n = 900) were recruited and randomized into 6 groups, to receive de-escalating doses of 17DD-YFV, from 27,476 IU to 31 IU. Blood samples were collected before vaccination (for neutralization tests to yellow fever, serology for dengue and clinical chemistry), 3 to 7 d after vaccination (for viremia and clinical chemistry) and 30 d after vaccination (for new yellow fever serology and clinical chemistry). Adverse events diaries were filled out by volunteers during 10 d after vaccination. Volunteers were retested for yellow fever and dengue antibodies 10 mo later. Seropositivity for dengue was found in 87.6% of volunteers before vaccination, but this had no significant influence on conclusions.

CONCLUSION

In young healthy adults Bio-Manguinhos/Fiocruz yellow fever vaccine can be used in much lower doses than usual. INTERNATIONAL REGISTER: ISRCTN 38082350.

Mechanistic insights into the impairment of memory B cells and antibody production in the elderly

It is well established that immunologic memory generated early in life can be maintained into old age and mediate robust anamnestic antibody responses. Little is known, however, about the initiation of memory B cells in the elderly. We have conducted a prospective analysis of the quantities and functionalities of antigen-specific B cell responses and its association with the functional helper CD4(+)T cell responses. The ability of naïve B cells from old (60-80 years) and young (20-31 years) humans to establish functional memory was examined following primary and booster vaccination with an inactivated-virus vaccine against tick-borne encephalitis. Our data show that the number of antigen-specific memory B cells generated during primary vaccination was ~3-fold lower in old than in young individuals. The maintenance and booster responsiveness of these memory B cells were not compromised, as evidenced by similar increases in specific memory B cell frequencies upon revaccination in old and young adults. In contrast, the Ab response mediated per memory B cell after revaccination was dramatically diminished in the elderly. Also, antigen-specific IL-2-positive CD4(+)T cell responses were strongly reduced in the elderly and displayed an excellent correlation with Ab titres. The data suggest that the dramatically lower antibody response in the elderly could only partially be accounted for by the reduced B cell numbers and was strongly correlated with profound functional defects in CD4 help.

Active assessment of adverse events following yellow fever vaccination of persons aged 60 years and more

INTRODUCTION

Older age has been associated to serious adverse events (AE) following yellow fever (YF) vaccination in passive surveillance studies, but few prospective studies involving seniors have been published.

RESULTS

A total of 906 persons were evaluated; 78 were not vaccinated and 828 received the vaccine; 700 (84.7%) were interviewed after vaccination: 593 (84.7%) did not report any symptoms or signs following YF vaccine; 107 (15.3%) reported at least one AE temporally associated to YF vaccination: 97 (13.9%) had systemic AE and 17 (2.4%) reported AE at the injection site (7 had both systemic and local AE). Data regarding previous vaccination was available for 655 subjects. Statistically significant higher rates of systemic AE were observed among subjects who received the first YF vaccination (17.5%) in comparison to persons who had been previously vaccinated (9.5%).

METHODS

This observational prospective study aimed to describe AE following YF vaccination in persons aged ≥ 60 y. From March 2009 to April 2010, seniors who sought YF vaccination at a reference Immunization Center in São Paulo city, Brazil, were included. Demographic and clinical data, previous YF vaccination, travel destination and the final decision regarding YF vaccination or not were collected from standardized medical records. Active AE assessment was done through telephone or electronic mail interview performed approximately 14 d after immunization.

CONCLUSION

Most persons aged ≥ 60 y may be safely vaccinated against YF. Before vaccination, they must be carefully screened for conditions associated to altered immunocompetence and for risk of exposure to YF.

A randomized, double-blind, controlled trial of the 17D yellow fever virus vaccine given in combination with immune globulin or placebo: comparative viremia and immunogenicity

We evaluated whether coadministration of the yellow fever (YF) virus vaccine with human immunoglobulin (Ig) that contained YF virus-neutralizing antibodies would reduce post-vaccination viremia without compromising immunogenicity and thus, potentially mitigate YF vaccine-associated adverse events. We randomized 80 participants to receive either YF vaccine and Ig or YF vaccine and saline placebo. Participants were followed for 91 days for safety and assessments of viremia and immunogenicity. There were no differences found between the two groups in the proportion of vaccinated participants who developed viremia, seroconversion, cluster of differentiation (CD)-8(+) and CD4(+) T-cell responses, and cytokine responses. These results argue against one putative explanation for the increased reporting of YF vaccine side effects in recent years (i.e., a change in travel clinic practice after 1996 when hepatitis A prophylaxis with vaccine replaced routine use of pre-travel Ig, thus potentially removing an incidental YF vaccine-attenuating effect of anti-YF virus antibodies present in Ig).

Evolution and medicine in undergraduate education: a prescription for all biology students

The interface between evolutionary biology and the biomedical sciences promises to advance understanding of the origins of genetic and infectious diseases in humans, potentially leading to improved medical diagnostics, therapies, and public health practices. The biomedical sciences also provide unparalleled examples for evolutionary biologists to explore. However, gaps persist between evolution and medicine, for historical reasons and because they are often perceived as having disparate goals. Evolutionary biologists have a role in building a bridge between the disciplines by presenting evolutionary biology in the context of human health and medical practice to undergraduates, including premedical and preprofessional students. We suggest that students will find medical examples of evolution engaging. By making the connections between evolution and medicine clear at the undergraduate level, the stage is set for future health providers and biomedical scientists to work productively in this synthetic area. Here, we frame key evolutionary concepts in terms of human health, so that biomedical examples may be more easily incorporated into evolution courses or more specialized courses on evolutionary medicine. Our goal is to aid in building the scientific foundation in evolutionary biology for all students, and to encourage evolutionary biologists to join in the integration of evolution and medicine.

Yellow fever virus vaccine-associated deaths in young women

Yellow fever vaccine–associated viscerotropic disease is a rare sequela of live-attenuated virus vaccine. Elderly persons and persons who have had thymectomies have increased susceptibility. A review of published and other data suggested a higher than expected number of deaths from yellow fever vaccine–associated viscerotropic disease among women 19–34 years of age without known immunodeficiency.

The safety of yellow fever vaccine 17D or 17DD in children, pregnant women, HIV+ individuals, and older persons: systematic review

Yellow fever vaccine provides long-lasting immunity. Rare serious adverse events after vaccination include neurologic or viscerotropic syndromes or anaphylaxis. We conducted a systematic review of adverse events associated with yellow fever vaccination in vulnerable populations. Nine electronic bibliographic databases and reference lists of included articles were searched. Electronic databases identified 2,415 abstracts for review, and 32 abstracts were included in this review. We identified nine studies of adverse events in infants and children, eight studies of adverse events in pregnant women, nine studies of adverse events in human immunodeficiency virus-positive patients, five studies of adverse events in persons 60 years and older, and one study of adverse events in individuals taking immunosuppressive medications. Two case studies of maternal-neonate transmission resulted in serious adverse events, and the five passive surveillance databases identified very small numbers of cases of yellow fever vaccine-associated viscerotropic disease, yellow fever vaccine-associated neurotropic disease, and anaphylaxis in persons ≥ 60 years. No other serious adverse events were identified in the other studies of vulnerable groups.

Learning vaccinology from viral infections

This issue of the Journal of Experimental Medicine celebrates and honors the life of Ralph Steinman (1943-2011), winner of the 2011 Nobel Prize in Physiology or Medicine. Ralph's science was rooted in fundamental discovery with the goal of translating these findings into clinical medicine. He recognized the power of immunology in treating human disease and passionately championed studies on vaccine design, immune therapy, and human immunology. One particular collaborative effort between the Steinman and Sekaly laboratories resulted in a paper published in this issue of the journal.

Intradermal vaccination to protect against yellow fever and influenza

The viral infections yellow fever and influenza can lead to large epidemics, which may deplete limited vaccine supplies. The intradermal vaccination route of yellow fever and influenza vaccines has received renewed attention, because it allows dose reduction without loss of efficacy. In this chapter, we review these two vaccines, the history of vaccine development, correlates of protection, immune response to vaccination and current knowledge concerning intradermal vaccination, including the immunological background, both in healthy subjects and immunocompromized individuals.

Heterotypic dengue infection with live attenuated monotypic dengue virus vaccines: implications for vaccination of populations in areas where dengue is endemic

BACKGROUND

Because infection with any of the 4 Dengue virus serotypes may elicit both protective neutralizing antibodies and nonneutralizing antibodies capable of enhancing subsequent heterotypic Dengue virus infections, the greatest risk for severe dengue occurs during a second, heterotypic Dengue virus infection. It remains unclear whether the replication of live attenuated vaccine viruses will be similarly enhanced when administered to Dengue-immune individuals.

METHODS

We recruited 36 healthy adults who had previously received a monovalent live Dengue virus vaccine 0.6-7.4 years earlier. Participants were assigned to 1 of 4 cohorts and were randomly chosen to receive placebo or a heterotypic vaccine. The level of replication, safety, and immunogenicity of the heterotypic vaccine virus was compared with that of Dengue virus immunologically naive vaccinees.

RESULTS

Vaccine virus replication and reactogenicity after monovalent Dengue virus vaccination in naive and heterotypically immune vaccinees was similar. In contrast to naive vaccinees, the antibody response in heterotypically immune vaccinees was broadly neutralizing and mimicked the response observed by natural secondary Dengue virus infection.

CONCLUSIONS

Enhanced replication of these live attenuated Dengue virus vaccines was minimal in heterotypically immune vaccinees and suggests that the further evaluation of these candidate vaccines in populations with preexisting DENV immunity can proceed safely.

Treatment of yellow fever

Yellow fever (YF) is a life-threatening mosquito-borne flaviviral hemorrhagic fever (VHF) characterized by severe hepatitis, renal failure, hemorrhage, and rapid terminal events with shock and multi-organ failure. A live, attenuated vaccine (YF 17D), in wide use for over 60 years, causes a disease identical to wild-type virus at an incidence of 2.5x10(-6). Our current understanding of the pathogenesis and treatment of YF (described in this brief review) is derived from studies of animal models (macaques, hamsters) that reproduce the features of human YF and from descriptive studies of human cases of naturally acquired and vaccine-associated VHF. The least understood, but potentially most important terminal events appear to be due to 'cytokine storm' and represent a potential target for therapeutic interventions. Areas for future study include dissection of cytokine-mediated events in animal models, the pathogenic role of the profound neutrophilia that occurs pre-terminally, the (pathological) role of adaptive immune clearance in pathogenesis, and treatments directed at cytokine storm. Antibody, interferon-alpha, polyICLC and other immune modulators are highly effective when administered before or within a narrow time window after infection, but are ineffective when given after the infection is established. A few antivirals have been evaluated (ribavirin, tiazofurin, carboxamide, pyrazoline compounds). Ribavirin has been used successfully to treat hamsters when the drug is given at high doses up to 2 days after virus infection (shortly before liver infection), but has not shown promise in nonhuman primate models. Future work should focus on evaluating higher doses of ribavirin alone or in combinations with potentially synergistic drugs, including interferons. Also specific inhibitors against other flaviviruses such as dengue virus should be investigated for potential pan-flavivirus activity since recent studies have shown that specific targets such as the flavivirus proteases and helicases are very similar in structure.