Use of Anthrax Vaccine in the United States: Recommendations of the Advisory Committee on Immunization Practices, 2019

Rapid in vitro activity of telavancin against Bacillus anthracis and in vivo protection against inhalation anthrax infection in the rabbit model

Inhalation anthrax is the most severe form of Bacillus anthracis infection, often progressing to fatal conditions if left untreated. While recommended antibiotics can effectively treat anthrax when promptly administered, strains engineered for antibiotic resistance could render these drugs ineffective. Telavancin, a semisynthetic lipoglycopeptide antibiotic, was evaluated in this study as a novel therapeutic against anthrax disease. Specifically, the aims were to (i) assess in vitro potency of telavancin against 17 B. anthracis isolates by minimum inhibitory concentration (MIC) testing and (ii) evaluate protective efficacy in rabbits infected with a lethal dose of aerosolized anthrax spores and treated with human-equivalent intravenous telavancin doses (30 mg/kg every 12 hours) for 5 days post-antigen detection versus a humanized dose of levofloxacin and vehicle control. Blood samples were collected at various times post-infection to assess the level of bacteremia and antibody production, and tissues were collected to determine bacterial load. The animals' body temperatures were also recorded. Telavancin demonstrated potent bactericidal activity against all strains tested (MICs 0.06-0.125 μg/mL). Further, telavancin conveyed 100% survival in this model and cleared B. anthracis from the bloodstream and organ tissues more effectively than a humanized dose of levofloxacin. Collectively, the low MICs against all strains tested and rapid bactericidal in vivo activity demonstrate that telavancin has the potential to be an effective alternative for the treatment or prophylaxis of anthrax infection.

Vaccine Development

This article considers ethical considerations surrounding pediatric vaccine development for pandemic preparedness, examines some historical cases of pediatric vaccines developed during past smallpox, influenza, and 2019 coronavirus disease pandemics, and discusses the current state of vaccine development for pandemic preparedness, including vaccines against smallpox/mpox, influenza, anthrax, and Ebola that are included in the US Strategic National Stockpile and vaccines being developed against priority pathogens identified by the World Health Organization.

CDC Guidelines for the Prevention and Treatment of Anthrax, 2023

This report updates previous CDC guidelines and recommendations on preferred prevention and treatment regimens regarding naturally occurring anthrax. Also provided are a wide range of alternative regimens to first-line antimicrobial drugs for use if patients have contraindications or intolerances or after a wide-area aerosol release of

Bacillus anthracis spores if resources become limited or a multidrug-resistant B. anthracis strain is used (Hendricks KA, Wright ME, Shadomy SV, et al.; Workgroup on Anthrax Clinical Guidelines. Centers for Disease Control and Prevention expert panel meetings on prevention and treatment of anthrax in adults. Emerg Infect Dis 2014;20:e130687; Meaney-Delman D, Rasmussen SA, Beigi RH, et al. Prophylaxis and treatment of anthrax in pregnant women. Obstet Gynecol 2013;122:885-900; Bradley JS, Peacock G, Krug SE, et al. Pediatric anthrax clinical management. Pediatrics 2014;133:e1411-36). Specifically, this report updates antimicrobial drug and antitoxin use for both postexposure prophylaxis (PEP) and treatment from these previous guidelines best practices and is based on systematic reviews of the literature regarding 1) in vitro antimicrobial drug activity against B. anthracis; 2) in vivo antimicrobial drug efficacy for PEP and treatment; 3) in vivo and human antitoxin efficacy for PEP, treatment, or both; and 4) human survival after antimicrobial drug PEP and treatment of localized anthrax, systemic anthrax, and anthrax meningitis.

Changes from previous CDC guidelines and recommendations include an expanded list of alternative antimicrobial drugs to use when first-line antimicrobial drugs are contraindicated or not tolerated or after a bioterrorism event when first-line antimicrobial drugs are depleted or ineffective against a genetically engineered resistant

B. anthracis strain. In addition, these updated guidelines include new recommendations regarding special considerations for the diagnosis and treatment of anthrax meningitis, including comorbid, social, and clinical predictors of anthrax meningitis. The previously published CDC guidelines and recommendations described potentially beneficial critical care measures and clinical assessment tools and procedures for persons with anthrax, which have not changed and are not addressed in this update. In addition, no changes were made to the Advisory Committee on Immunization Practices recommendations for use of anthrax vaccine (Bower WA, Schiffer J, Atmar RL, et al. Use of anthrax vaccine in the United States: recommendations of the Advisory Committee on Immunization Practices, 2019. MMWR Recomm Rep 2019;68[No. RR-4]:1-14). The updated guidelines in this report can be used by health care providers to prevent and treat anthrax and guide emergency preparedness officials and planners as they develop and update plans for a wide-area aerosol release of B. anthracis.

Modeling on the Effects of Deliberate Release of Aerosolized Inhalational Bacillus anthracis (Anthrax) on an Australian Population

This study aimed to determine optimal mitigation strategies in the event of an aerosolized attack with Bacillus anthracis, a category A bioterrorism agent with a case fatality rate of nearly 100% if inhaled and untreated. To simulate the effect of an anthrax attack, we used a plume dispersion model for Sydney, Australia, accounting for weather conditions. We determined the radius of exposure in different sizes of attack scenarios by spore quantity released per second. Estimations of different spore concentrations were then used to calculate the exposed population to inform a Susceptible-Exposed-Infected-Recovered (SEIR) deterministic mathematical model. Results are shown as estimates of the total number of exposed and infected people, along with the burden of disease, to quantify the amount of vaccination and antibiotics doses needed for stockpiles. For the worst-case scenario, over 500,000 people could be exposed and over 300,000 infected. The number of deaths depends closely on timing to start postexposure prophylaxis. Vaccination used as a postexposure prophylaxis in conjunction with antibiotics is the most effective mitigation strategy to reduce deaths after an aerosolized attack and is more effective when the response starts early (2 days after release) and has high adherence, while it makes only a small difference when started late (after 10 days).

Antitoxin Use in the Prevention and Treatment of Anthrax Disease: A Systematic Review

BACKGROUND

Bacillus anthracis is a high-priority threat agent because of its widespread availability, easy dissemination, and ability to cause substantial morbidity and mortality. Although timely and appropriate antimicrobial therapy can reduce morbidity and mortality, the role of adjunctive therapies continues to be explored.

METHODS

We searched 11 databases for articles that report use of anthrax antitoxins in treatment or prevention of systemic anthrax disease published through July 2019. We identified other data sources through reference search and communication with experts. We included English-language studies on antitoxin products with approval by the US Food and Drug Administration (FDA) for anthrax in humans, nonhuman primates, and rabbits. Two researchers independently reviewed studies for inclusion and abstracted relevant data.

RESULTS

We abstracted data from 12 publications and 2 case reports. All 3 FDA-approved anthrax antitoxins demonstrated significant improvement in survival as monotherapy over placebo in rabbits and nonhuman primates. No study found significant improvement in survival with combination antitoxin and antimicrobial therapy compared to antimicrobial monotherapy. Case reports and case series described 25 patients with systemic anthrax disease treated with antitoxins; 17 survived. Animal studies that used antitoxin monotherapy as postexposure prophylaxis (PEP) demonstrated significant improvement in survival over placebo, with greatest improvements coming with early administration.

CONCLUSIONS

Limited human and animal evidence indicates that adjunctive antitoxin treatment may improve survival from systemic anthrax infection. Antitoxins may also provide an alternative therapy to antimicrobials for treatment or PEP during an intentional anthrax incident that could involve a multidrug-resistant B. anthracis strain.

Vaccine Preventable Zoonotic Diseases: Challenges and Opportunities for Public Health Progress

Zoonotic diseases represent a heavy global burden, causing important economic losses, impacting animal health and production, and costing millions of human lives. The vaccination of animals and humans to prevent inter-species zoonotic disease transmission is an important intervention. However, efforts to develop and implement vaccine interventions to reduce zoonotic disease impacts are often limited to the veterinary and agricultural sectors and do not reflect the shared burden of disease. Multisectoral collaboration, including co-development opportunities for human and animal vaccines, expanding vaccine use to include animal reservoirs such as wildlife, and strategically using vaccines to interrupt complex transmission cycles is needed. Addressing zoonoses requires a multi-faceted One Health approach, wherein vaccinating people and animals plays a critical role.

Welder’s Anthrax: A Review of an Occupational Disease

Since 1997, nine cases of severe pneumonia, caused by species within the B. cereus group and with a presentation similar to that of inhalation anthrax, were reported in seemingly immunocompetent metalworkers, with most being welders. In seven of the cases, isolates were found to harbor a plasmid similar to the B. anthracis pXO1 that encodes anthrax toxins. In this paper, we review the literature on the B. cereus group spp. pneumonia among welders and other metalworkers, which we term welder’s anthrax. We describe the epidemiology, including more information on two cases of welder’s anthrax in 2020. We also describe the health risks associated with welding, potential mechanisms of infection and pathological damage, prevention measures according to the hierarchy of controls, and clinical and public health considerations. Considering occupational risk factors and controlling exposure to welding fumes and gases among workers, according to the hierarchy of controls, should help prevent disease transmission in the workplace.

Systematic analysis of drug-associated myocarditis reported in the World Health Organization pharmacovigilance database

While multiple pharmacological drugs have been associated with myocarditis, temporal trends and overall mortality have not been reported. Here we report the spectrum and main features of 5108 reports of drug-induced myocarditis, in a worldwide pharmacovigilance analysis, comprising more than 21 million individual-case-safety reports from 1967 to 2020. Significant association between myocarditis and a suspected drug is assessed using disproportionality analyses, which use Bayesian information component estimates. Overall, we identify 62 drugs associated with myocarditis, 41 of which are categorized into 5 main pharmacological classes: antipsychotics (n = 3108 reports), salicylates (n = 340), antineoplastic-cytotoxics (n = 190), antineoplastic-immunotherapies (n = 538), and vaccines (n = 790). Thirty-eight (61.3%) drugs were not previously reported associated with myocarditis. Antipsychotic was the first (1979) and most reported class (n = 3018). In 2019, the two most reported classes were antipsychotics (54.7%) and immunotherapies (29.5%). Time-to-onset between treatment start and myocarditis is 15 [interquartile range: 10; 23] days. Subsequent mortality is 10.3% and differs between drug classes with immunotherapies the highest, 32.5% and salicylates the lowest, 2.6%. These elements highlight the diversity of presentations of myocarditis depending on drug class, and show the emerging role of antineoplastic drugs in the field of drug-induced myocarditis.

Vaccines

The safety of COVID-19 vaccines, as was the case last year, remains a large part of the focus in this volume. COVID-19 placed a large magnifying glass on both vaccines, specifically vaccine safety. This was most readily apparent as the number of records in VAERS ballooned to about 10 times the size from 2020 to 2021 (Vaccine Adverse Event Reporting System (VAERS), 2022) [S]. While we have added and/or improved VAERS during COVID-19, including adding or improving other vaccine safety surveillance tools like v-safe and vaccine safety datalink (Blumenthal, Phadke, et al., 2021) [MC], there is still room for improvement in these pharmacovigilance tools (Rizk et al., 2021) [r]. A major global initiative in this realm is the Global Vaccines Safety Blueprint 2.0 (GVSB2.0) (Organization, 2021, pp. 2021–2023) [S]. We wholeheartedly endorse these initiatives, which could significantly improve vaccine safety.

As noted in past SEDA issues, clinicians should be mindful of the risks of AEs and SAEs associated with each individual vaccine.

Safety and immunogenicity of Px563L, a recombinant anthrax vaccine candidate, in a two-dose regimen for post-exposure prophylaxis in healthy adults

Px563L is a next-generation anthrax vaccine candidate consisting of a protein subunit, mutant recombinant protective antigen SNKE167-ΔFF-315-E308D (mrPA), and liposome-embedded monophosphoryl lipid A (MPLA) adjuvant. Px563L has the potential to deliver an improved safety and immunogenicity profile relative to the currently licensed vaccine, which is produced from filtered B. anthracis culture supernatants. We conducted a Phase 1, double-blind, placebo-controlled, dose-escalation study in 54 healthy subjects to evaluate Px563L at 3 dose levels of mrPA (10, 50, and 80 mcg). For each dose level, 18 subjects were randomized in an 8:8:2 ratio to Px563L (mrPA with adjuvant), RPA563 (mrPA only) or placebo (saline). Each subject received an intramuscular (IM) injection on Day 0 and Day 28. Primary safety and immunogenicity analysis was conducted after all subjects completed the Day70 visit, a duration deemed clinically relevant for post-exposure prophylaxis. Long-term safety was assessed through Day 393. Vaccinations with Px563L at all dose levels were well-tolerated. There were no serious adverse events or adverse events (AE) leading to early withdrawal. In all treatment groups, most AEs were due to injection site reactions, and all AEs at the 10 and 50 mcg dose levels were mild. For the primary immunogenicity endpoint (protective toxin neutralizing antibody 50% neutralization factor [TNA NF₅₀]), titers started to increase significantly after the second administration of Px563L, from Day35 through Day70, with the geometric mean and lower bound of the 95% confidence interval exceeding 0.56, a threshold correlating with significant survival in animal models of anthrax exposure. In conclusion, Px563L, administered as two IM doses 28 days apart, was well-tolerated and elicited a protective antibody response starting at seven days after the second vaccination. These findings support the continued development of Px563L in a two-dose regimen for anthrax post-exposure prophylaxis. ClinicalTrials.gov identifier NCT02655549.

Single-dose combination nanovaccine induces both rapid and durable humoral immunity and toxin neutralizing antibody responses against Bacillus anthracis

Bacillus anthracis, the causative agent of anthrax, continues to be a prominent biological warfare and bioterrorism threat. Vaccination is likely to remain the most effective and user-friendly public health measure to counter this threat in the foreseeable future. The commercially available AVA BioThrax vaccine has a number of shortcomings where improvement would lead to a more practical and effective vaccine for use in the case of an exposure event. Identification of more effective adjuvants and novel delivery platforms is necessary to improve not only the effectiveness of the anthrax vaccine, but also enhance its shelf stability and ease-of-use. Polyanhydride particles have proven to be an effective platform at adjuvanting the vaccine-associated adaptive immune response as well as enhancing stability of encapsulated antigens. Another class of adjuvants, the STING pathway-targeting cyclic dinucleotides, have proven to be uniquely effective at inducing a beneficial inflammatory response that leads to the rapid induction of high titer antibodies post-vaccination capable of providing protection against bacterial pathogens. In this work, we evaluate the individual contributions of cyclic di-GMP (CDG), polyanhydride nanoparticles, and a combination thereof towards inducing neutralizing antibody (nAb) against the secreted protective antigen (PA) from B. anthracis. Our results show that the combination nanovaccine elicited rapid, high titer, and neutralizing IgG anti-PA antibody following single dose immunization that persisted for at least 108 DPI.

A qualitative exploratory study using One Health approach for developing an intervention package for elimination of human anthrax in an endemic district of Odisha, India

Background & objectives:

Anthrax is a zoonotic disease of public health concern in India. One of the key predisposing factors is linked to the behaviour of the community. This study was nested within a baseline survey to understand the risk perception, attitude, socio-cultural and behavioural practices among different communities in an anthrax endemic tribal district of Odisha, India. It was aimed to explore the systemic gaps from the officials of different departments while addressing the animal and human anthrax cases and the knowledge, attitude, and behavioural practices among the tribal communities with regards to both animal and human anthrax signs, symptoms, and transmission from animal to human.

Methods:

A qualitative exploratory study was carried out in the district of Koraput, Odisha. Insights from eight focus group discussions (FGDs) and 42 in-depth-interviews (IDIs) with the stakeholders from health, veterinary, forest, general administrative departments and community were collected and analyzed thematically.

Results:

Major themes that emerged were inter-departmental coordination, livestock vaccination, surveillance network, laboratory facilities, prevention and control strategies with regards to the animal and human anthrax cases. The study also emphasized setting up the surveillance system as per the standard guidelines, and strengthening the diagnostic facilities for timely detection of confirmed cases. It also highlighted the current needs and the gaps among inter-sectoral coordination, collaboration, and sensitization among Health, Veterinary, Forest, Education, Nutrition, and Tribal Welfare Departments at various levels to reduce the prevalence and control the outbreaks of anthrax in the district and State.

Interpretation & conclusions:

The coordination gaps, financial burden, insufficient relevant knowledge and information among the concerned stakeholders were the issues found in this study in addition to non-availability of proper diagnostic facility. The coordination among different departments adapting One Health approach may be one of the best possible ways for the elimination of anthrax cases in an endemic region.

Vaccines

In this volume of the Side Effects of Drugs Annual, although other vaccines will be covered, the safety of COVID vaccines is the focus as COVID-19 has led to heightened attention on vaccine safety in general. As such, this chapter will be more relevant than ever before. As noted in past SEDA issues, clinicians should be mindful of the risks of AEs and SAEs associated with each vaccine.

Control and Prevention of Anthrax, Texas, USA, 2019

The zoonotic disease anthrax is endemic to most continents. It is a disease of herbivores that incidentally infects humans through contact with animals that are ill or have died from anthrax or through contact with Bacillus anthracis-contaminated byproducts. In the United States, human risk is primarily associated with handling carcasses of hoofstock that have died of anthrax; the primary risk for herbivores is ingestion of B. anthracis spores, which can persist in suitable alkaline soils in a corridor from Texas through Montana. The last known naturally occurring human case of cutaneous anthrax associated with livestock exposure in the United States was reported from South Dakota in 2002. Texas experienced an increase of animal cases in 2019 and consequently higher than usual human risk. We describe the animal outbreak that occurred in southwest Texas beginning in June 2019 and an associated human case. Primary prevention in humans is achieved through control of animal anthrax.

Efficacy of the AV7909 anthrax vaccine candidate in guinea pigs and nonhuman primates following two immunizations two weeks apart

The anthrax vaccine candidate AV7909 is being developed as a next-generation vaccine for post-exposure prophylaxis (PEP) against inhalational anthrax. In clinical studies, two vaccinations with AV7909 administered either two or four weeks apart induced an enhanced immune response compared to BioThrax® (Anthrax Vaccine Adsorbed) (AVA). Anthrax toxin-neutralizing antibody (TNA) levels on Day 70 following initial vaccination that were associated with protection of animals exposed to inhalational anthrax were previously reported for the 0, 4-week AV7909 vaccination regimen. The current study shows that a 0, 2-week AV7909 vaccination regimen protected guinea pigs (GPs) and nonhuman primates (NHPs) against a lethal inhalational anthrax challenge on Days 28 and 70 after the first immunization. An earlier induction of protective TNA levels using a 0, 2-week AV7909 vaccination regimen may provide benefit over the currently approved AVA PEP 0, 2, and 4-week vaccination regimen.

A serological survey of Bacillus anthracis reveals widespread exposure to the pathogen in free-range and captive lions in Zimbabwe

Numerous unknown factors influence anthrax epidemiology in multi-host systems, especially at wildlife/livestock/human interfaces. Serology tests for anti-anthrax antibodies in carnivores are useful tools in identifying the presence or absence of Bacillus anthracis in a range. These were employed to ascertain whether the disease pattern followed the recognized high- and low-risk anthrax zonation in Zimbabwe and also to establish whether anthrax was absent from Hwange National Park in which there have been no reported outbreaks. African lions (Panthera leo) (n = 114) drawn from free-range protected areas and captive game parks located in recognized high- and low-risk zones across Zimbabwe were tested for antibodies to anthrax PA antigen using the ELISA immunoassay. A random selection of 27 lion sera samples comprising 17 seropositive and 10 seronegative sera was further tested in the species-independent toxin neutralization assay (TNA) in order to validate the former as a surveillance tool for anthrax in African lions. Using the ELISA-PA immunoassay, 21.9% (25/114) of the lions tested positive for antibodies to anthrax. Seropositivity was recorded in all study areas, and there was no significant difference (p = .852) in seropositivity between lions in high- and low-risk anthrax zones. Also, there was no significant difference (McNemar's chi-square test = 0.9, p = .343) in the proportion of lions testing positive to anti-PA anthrax antibodies on ELISA-PA immunoassay compared with the TNA, with fair agreement between the two tests [kappa (K) statistic = 0.30; 0.08 < K<0.613]. Results of this study indicate that anthrax could be more widespread than 42 currently realized in Zimbabwe, and present in recognized high- and low-risk zones, including 43 where it has not been reported in over 20 years such as Hwange National Park. This is also the 44 first report documenting the presence of anthrax lethal toxin-neutralizing antibodies in naturally 45 infected carnivores, further confirming exposure to B. anthracis. The research results point to a 46 need for revisiting the currently recognized anthrax risk zones in Zimbabwe. This should be based 47 on improved surveillance of the disease in both wild and domestic animals for better understanding and control of the disease.

Teixobactin Provides Protection against Inhalation Anthrax in the Rabbit Model

The use of antibiotics is a vital means of treating infections caused by the bacteria Bacillus (B.) anthracis. Importantly, with the potential future use of multidrug-resistant strains of B. anthracis as bioweapons, new antibiotics are needed as alternative therapeutics. In this blinded study, we assessed the protective efficacy of teixobactin, a recently discovered antibiotic, against inhalation anthrax infection in the adult rabbit model. New Zealand White rabbits were infected with a lethal dose of B. anthracis Ames spores via the inhalation route, and blood samples were collected at various times to assess antigenemia, bacteremia, tissue bacterial load, and antibody production. Treatments were administered upon detection of B. anthracis protective antigen in the animals’ sera. For comparison, a fully protective dose of levofloxacin was used as a positive control. Rabbits treated with teixobactin showed 100% survival following infection, and the bacteremia was completely resolved by 24–48 h post-treatment. In addition, the bacterial/spore loads in tissues of the animals treated with teixobactin were either zero or dramatically less relative to that of the negative control animals. Moreover, microscopic evaluation of the tissues revealed decreased pathology following treatment with teixobactin. Overall, these results show that teixobactin was protective against inhalation anthrax infection in the rabbit model, and they indicate the potential of teixobactin as a therapeutic for the disease.

Current Status and Trends in Prophylaxis and Management of Anthrax Disease

Bacillus anthracis has been identified as a potential military and bioterror agent as it is relatively simple to produce, with spores that are highly resilient to degradation in the environment and easily dispersed. These characteristics are important in describing how anthrax could be used as a weapon, but they are also important in understanding and determining appropriate prevention and treatment of anthrax disease. Today, anthrax disease is primarily enzootic and found mostly in the developing world, where it is still associated with considerable mortality and morbidity in humans and livestock. This review article describes the spectrum of disease caused by anthrax and the various prevention and treatment options. Specifically we discuss the following; (1) clinical manifestations of anthrax disease (cutaneous, gastrointestinal, inhalational and intravenous-associated); (2) immunology of the disease; (3) an overview of animal models used in research; (4) the current World Health Organization and U.S. Government guidelines for investigation, management, and prophylaxis; (5) unique regulatory approaches to licensure and approval of anthrax medical countermeasures; (6) the history of vaccination and pre-exposure prophylaxis; (7) post-exposure prophylaxis and disease management; (8) treatment of symptomatic disease through the use of antibiotics and hyperimmune or monoclonal antibody-based antitoxin therapies; and (9) the current landscape of next-generation product candidates under development.

The Landscape of Anthrax Prevention and Control: Stakeholders' Perceptive in Odisha, India

The prevalence and outbreaks of anthrax are interlinked with the animal-environment-human context, which signifies the need for collaborative, trans-disciplinary and multi-sectoral approaches for the prevention and control of anthrax. In India, there are hardly any shreds of evidence on the role of various stakeholders' on anthrax prevention and control. Therefore, this study addressed the experiences of various stakeholders on anthrax prevention and control strategies in Odisha, India. A qualitative explorative study was carried out using 42 in-depth-interviews among the stakeholders from health, veterinary and general administrative departments from the block, district, and state level. Two major themes emerged: (1) Epidemiological investigation of anthrax in Odisha, India, and (2) Biological and social prevention strategies for anthrax in Odisha, India. The study emphasizes setting up the surveillance system as per standard guideline, and strengthening the diagnostic facility at a regional medical college laboratory to avoid delay. Moreover, it emphasizes step-up inter-sectoral co-ordination, collaboration and sensitization among health, veterinary, forestry, education, nutrition and tribal welfare departments at all levels in order to reduce the prevalence and control the outbreaks of anthrax in Odisha state. It also recommends raising community literacy, in particular on safe carcass disposal, changing behavior on dead-livestock consumption, and compliance with livestock vaccinations.

Current State of Anthrax Vaccines and Key R&D Gaps Moving Forward

A licensed anthrax vaccine has been available for pre-exposure prophylaxis in the United States since 1970, and it was approved for use as a post-exposure prophylaxis, in combination with antibiotic treatment, in 2015. A variety of other vaccines are available in other nations, approved under various regulatory frameworks. However, investments in anthrax vaccines continue due to the severity of the threat posed by this bacterium, as both a naturally occurring pathogen and the potential for use as a bioweapon. In this review, we will capture the current landscape of anthrax vaccine development, focusing on those lead candidates in clinical development. Although approved products are available, a robust pipeline of candidate vaccines are still in development to try to address some of the key research gaps in the anthrax vaccine field. We will then highlight some of the most pressing needs in terms of anthrax vaccine research.

Effect of raxibacumab on immunogenicity of Anthrax Vaccine Adsorbed: a phase 4, open-label, parallel-group, randomised non-inferiority study

BACKGROUND

Raxibacumab is a monoclonal antibody against protective antigen, which is the cell-binding part of Bacillus anthracis toxin, and is approved for treatment and postexposure prophylaxis of inhalational anthrax. Anthrax Vaccine Adsorbed (AVA), for anthrax prophylaxis, consists primarily of adsorbed protective antigen. We did a postapproval study to assess the effect of raxibacumab on immunogenicity of AVA.

METHODS

We did an open-label, parallel-group, randomised non-inferiority study at three centres in the USA. We enrolled healthy volunteers (aged 18-65 years) with no evidence of exposure to protective antigen. Participants were randomly allocated (1:1) according to a pregenerated balanced independent randomisation schedule to either subcutaneous 0·5 mL AVA on days 1, 15, and 29 or raxibacumab intravenous infusion (40 mg/kg) immediately before AVA on day 1, followed by AVA only on days 15 and 29. It was an open-label study to investigators and participants; however, the sponsor remained blinded during the study. The primary outcome was the ratio of geometric mean concentrations (GMCs) of anti-protective antigen antibodies (attributable to the immune response to AVA) between AVA and AVA plus raxibacumab 4 weeks after the first AVA dose in the per-protocol population. The per-protocol population comprised all individuals who received the allocated treatment within the protocol-specified visit window and completed the primary study outcome assessment, without a protocol deviation requiring exclusion. The non-inferiority margin for the ratio of GMCs was predefined (upper limit of 90% CI <1·5). This trial is registered with ClinicalTrials.gov, NCT02339155.

FINDINGS

Between Feb 24, 2015, and June 6, 2017, 873 participants were screened for eligibility, of whom 300 were excluded. 573 were randomly allocated either AVA (n=287) or AVA plus raxibacumab (n=286). The per-protocol population comprised 276 individuals assigned AVA and 269 allocated AVA plus raxibacumab. At week 4, the GMC of anti-protective antigen antibodies in participants allocated AVA was 26·5 μg/mL (95% CI 23·6-29·8) compared with 22·5 μg/mL (20·1-25·1) among individuals allocated AVA plus raxibacumab. The ratio between groups was 1·18 (90% CI 1·03-1·35; p=0·0019), which met the predefined non-inferiority margin. Adverse events in the safety population were similar across groups (87 [30%] of 286 in the AVA group vs 80 [29%] of 280 in the AVA plus raxibacumab group) and no treatment-related serious adverse events were reported.

INTERPRETATION

Co-administration of raxibacumab with AVA does not negatively affect AVA immunogenicity. This finding suggests that combining raxibacumab with AVA might provide added benefit in postexposure prophylaxis against inhalational anthrax.

FUNDING

US Biomedical Advanced Research and Development Authority, and GlaxoSmithKline.