The Role of Brincidofovir in Preparation for a Potential Smallpox Outbreak

Brincidofovir: A Novel Agent for the Treatment of Smallpox

OBJECTIVE

This article reviews the published data encompassing the development, pharmacology, efficacy, and safety of brincidofovir, a nucleotide analogue DNA polymerase inhibitor developed for the treatment of smallpox.

DATA SOURCES

A literature review was conducted in PubMed, MEDLINE, and Clinicaltrials.gov from inception up to December 2022, using terms Tembexa, brincidofovir, CMX001, smallpox treatment, and variola treatment.

STUDY SELECTION AND DATA EXTRACTION

Data were limited to studies published in English language, which evaluated the efficacy and safety of brincidofovir.

DATA SYNTHESIS

Two surrogate animal models were included in the Food and Drug Administration's (FDA) decision to approve brincidofovir: ectromelia virus in mice and rabbitpox in rabbits. Phases 2 and 3 studies established safety for approval. Brincidofovir biweekly for the treatment of disseminated adenovirus disease resulted in all-cause mortality, ranging from 13.8% to 29%. In a study for cytomegalovirus prophylaxis, patients with clinically significant cytomegalovirus infection through week 24 posttransplant was 51.2% with brincidofovir and 52.3% with placebo.

CONCLUSIONS

Brincidofovir adds a second oral agent to treat smallpox, with a different mechanism of action than tecovirimat. In the event of a smallpox outbreak, prompt treatment will be necessary to contain its spread. Brincidofovir shows efficacy in surrogate animal models. In healthy volunteers and individuals treated, or used as prophylaxis, for cytomegalovirus or adenovirus, the primary adverse events were gastrointestinal in addition to transient hepatotoxicity. Additionally, excessive deaths were observed in hematopoietic cell transplant patients receiving it as cytomegalovirus prophylaxis, requiring a black box warning.

Identification of In Vitro Inhibitors of Monkeypox Replication

Monkeypox virus (MPXV) infections in humans have historically been restricted to regions of endemicity in Africa. However, in 2022, an alarming number of MPXV cases were reported globally, with evidence of person-to-person transmission. Because of this, the World Health Organization (WHO) declared the MPXV outbreak a public health emergency of international concern. The supply of MPXV vaccines is limited, and only two antivirals, tecovirimat and brincidofovir, approved by the U.S. Food and Drug Administration (FDA) for the treatment of smallpox, are currently available for the treatment of MPXV infection. Here, we evaluated 19 compounds previously shown to inhibit different RNA viruses for their ability to inhibit orthopoxvirus infections. We first used recombinant vaccinia virus (rVACV) expressing fluorescence (mScarlet or green fluorescent protein [GFP]) and luciferase (Nluc) reporter genes to identify compounds with antiorthopoxvirus activity. Seven compounds from the ReFRAME library (antimycin A, mycophenolic acid, AVN-944, pyrazofurin, mycophenolate mofetil, azaribine, and brequinar) and six compounds from the NPC library (buparvaquone, valinomycin, narasin, monensin, rotenone, and mubritinib) showed inhibitory activity against rVACV. Notably, the anti-VACV activity of some of the compounds in the ReFRAME library (antimycin A, mycophenolic acid, AVN-944, mycophenolate mofetil, and brequinar) and all the compounds from the NPC library (buparvaquone, valinomycin, narasin, monensin, rotenone, and mubritinib) were confirmed with MPXV, demonstrating their inhibitory activity in vitro against two orthopoxviruses. IMPORTANCE Despite the eradication of smallpox, some orthopoxviruses remain important human pathogens, as exemplified by the recent 2022 monkeypox virus (MPXV) outbreak. Although smallpox vaccines are effective against MPXV, access to those vaccines is limited. In addition, current antiviral treatment against MPXV infections is limited to the use of the FDA-approved drugs tecovirimat and brincidofovir. Thus, there is an urgent need to identify novel antivirals for the treatment of MPXV infection and other potentially zoonotic orthopoxvirus infections. Here, we show that 13 compounds, derived from two different libraries, previously found to inhibit several RNA viruses, also inhibit VACV. Notably, 11 compounds also displayed inhibitory activity against MPXV.

Clinical and Translational Pharmacology Considerations for Anti-infectives Approved Under the FDA Animal Rule

The US Food and Drug Administration's Animal Rule provides a pathway for approval of drugs and biologics aimed to treat serious or life-threatening conditions wherein traditional clinical trials are either not ethical or feasible. In such a scenario, determination of safety and efficacy are based on integration of data on drug disposition and drug action collected from in vitro models, infected animals, and healthy volunteer human studies. The demonstration of clinical efficacy and safety in humans based on robust, well-controlled animal studies is filled with challenges. This review elaborates on the challenges in the translation of data from in vitro and animal models to human dosing for antimicrobials. In this context, it discusses precedents of drugs approved under the Animal Rule, along with the approaches and guidance undertaken by sponsors.

Challenges in the treatment and prevention of Monkeypox infection; a comprehensive review

Human monkeypox (HMPX) is a zoonotic disease, literally meaning that it can be passed on from animals (non-primate) to human (primate). All the reported and recorded cases have been traced back either to international travel or import of African animals. In the Unites states, sporadic monkeypox cases have been reported in specific over the past 50 years, starting its first identification in the Democratic Republic of the Congo (D.R.C.) in 1970. Due to its extreme versatility, this disease poses threat as a serious public health issue that needs to be monitored, researched and prevented. Data indicate that prior immunization with the smallpox vaccine is beneficial and may provide protection against the monkeypox virus. JYNNEOSTM is a live viral vaccine that has been approved to improve clinical manifestations of the infection. On the other hand, public ignorance about safety precaution towards monkeypox post-COVID is another challenge that needs to be overcome in tackling HMPX as a possible re-emergent infection. This review is a collation of the epidemiology, etiology, transmission, clinical features and treatment of human monkeypox (HMPX).

Antivirals against monkeypox infections

Monkeypox virus (MPXV) infection in humans are historically restricted to endemic regions in Africa. However, in 2022, an alarming number of MPXV cases have been reported globally with evidence of person-to-person transmission. Because of this, the World Health Organization (WHO) declared the MPXV outbreak a public health emergency of international concern. MPXV vaccines are limited and only two antivirals, tecovirimat and brincidofovir, approved by the United States (US) Food and Drug Administration (FDA) for the treatment of smallpox, are currently available for the treatment of MPXV infection. Here, we evaluated 19 compounds previously shown to inhibit different RNA viruses for their ability to inhibit Orthopoxvirus infections. We first used recombinant vaccinia virus (rVACV) expressing fluorescence (Scarlet or GFP) and luciferase (Nluc) reporter genes to identify compounds with anti-Orthopoxvirus activity. Seven compounds from the ReFRAME library (antimycin A, mycophenolic acid, AVN- 944, pyrazofurin, mycophenolate mofetil, azaribine, and brequinar) and six compounds from the NPC library (buparvaquone, valinomycin, narasin, monensin, rotenone, and mubritinib) showed antiviral activity against rVACV. Notably, the anti-VACV activity of some of the compounds in the ReFRAME library (antimycin A, mycophenolic acid, AVN- 944, mycophenolate mofetil, and brequinar) and all the compounds from the NPC library (buparvaquone, valinomycin, narasin, monensin, rotenone, and mubritinib) were confirmed with MPXV, demonstrating the broad-spectrum antiviral activity against Orthopoxviruses and their potential to be used for the antiviral treatment of MPXV, or other Orthopoxvirus, infections.

IMPORTANCE

Despite the eradication of smallpox, some Orthopoxviruses remain important human pathogens, as exemplified by the recent 2022 monkeypox virus (MPXV) outbreak. Although smallpox vaccines are effective against MPXV, there is presently limited access to those vaccines. In addition, current antiviral treatment against MPXV infections is limited to the use of the FDA-approved drugs tecovirimat and brincidofovir. Thus, there is an urgent need to identify novel antivirals for the treatment of MPXV, and other potentially zoonotic Orthopoxvirus infections. Here, we show that thirteen compounds, derived from two different libraries, previously found to inhibit several RNA viruses, exhibit also antiviral activity against VACV. Notably, eleven compounds also displayed antiviral activity against MPXV, demonstrating their potential to be incorporated into the therapeutic armamentarium to combat Orthopoxvirus infections.

Therapeutics for treating mpox in humans

BACKGROUND

Mpox was declared a Public Health Emergency of International Concern (PHEIC) by the World Health Organization (WHO) on 23 July 2022, following the identification of thousands of cases in several non-endemic countries in previous months. There are currently no licenced therapeutics for treating mpox; however, some medications may be authorized for use in an outbreak. The efficacy and safety of possible therapeutic options has not been studied in humans with mpox. There is a need to investigate the evidence on safety and effectiveness of treatments for mpox in humans; should any therapeutic option be efficacious and safe, it may be approved for use around the world.

OBJECTIVES

There are two parts to this Cochrane Review: a review of evidence from randomized controlled trials (RCTs), and a narrative review of safety data from non-randomized studies. Randomized controlled trials review To systematically review the existing evidence on the effectiveness of therapeutics for mpox infection in humans compared to: a) another different therapeutic for mpox, or b) placebo, or c) supportive care, defined as the treatment of physical and psychological symptoms arising from the disease. Non-randomized studies review To assess the safety of therapeutics for mpox infection from non-randomized studies (NRS).

SEARCH METHODS

Randomized controlled trials review We searched the following databases up to 25 January 2023: MEDLINE (OVID), Embase (OVID), Biosis previews (Web of Science), CAB Abstracts (Web of science), and Cochrane CENTRAL (Issue 1 2023). We conducted a search of trial registries (Clinicaltrials.gov and International Clinical Trials Registry Platform (ICTRP)) on 25 January 2023. There were no date or language limits placed on the search. We undertook a call to experts in the field for relevant studies or ongoing trials to be considered for inclusion in the review. Non-randomized studies review We searched the following databases on 22 September 2022: Cochrane Central Register of Controlled Trials (CENTRAL; Issue 9 of 12, 2022), published in the Cochrane Library; MEDLINE (Ovid); Embase (Ovid); and Scopus (Elsevier). We also searched the WHO International Clinical Trials Registry Platform and ClinicalTrials.gov for trials in progress.

SELECTION CRITERIA

For the RCT review and the narrative review, any therapeutic for the treatment of mpox in humans was eligible for inclusion, including tecovirimat, brincidofovir, cidofovir, NIOCH-14, immunomodulators, and vaccine immune globulin. Randomized controlled trials review Studies were eligible for the main review if they were of randomized controlled design and investigated the effectiveness or safety of therapeutics in human mpox infection. Non-randomized studies review Studies were eligible for inclusion in the review of non-randomized studies if they were of non-randomized design and contained data concerning the safety of any therapeutic in human mpox infection.

DATA COLLECTION AND ANALYSIS

Randomized controlled trials review Two review authors independently applied study inclusion criteria to identify eligible studies. If we had identified any eligible studies, we planned to assess the risk of bias, and report results with 95% confidence intervals (CI). The critical outcomes were serious adverse events, development of disease-related complications, admission to hospital for non-hospitalized participants, pain as judged by any visual or numerical pain scale, level of virus detected in clinical samples, time to healing of all skin lesions, and mortality. We planned to perform subgroup analysis to explore whether the effect of the therapeutic on the planned outcomes was modified by disease severity and days from symptom onset to therapeutic administration. We also intended to explore the following subgroups of absolute effects: immunosuppression, age, and pre-existing skin disease. Non-randomized studies review One review author applied study inclusion criteria to identify eligible studies and extracted data. Studies of a non-randomized design containing data on the safety of therapeutics could not be meta-analyzed due to the absence of a comparator; we summarized these data narratively in an appendix.

MAIN RESULTS

Randomized controlled trials review We did not identify any completed RCTs investigating the effectiveness of therapeutics for treating mpox for the main review. We identified five ongoing trials that plan to assess the effectiveness of one therapeutic option, tecovirimat, for treating mpox in adults and children. One of these ongoing trials intends to include populations with, or at greater risk of, severe disease, which will allow an assessment of safety in more vulnerable populations. Non-randomized studies review Three non-randomized studies met the inclusion criteria for the narrative review, concerning data on the safety of therapeutics in mpox. Very low-certainty evidence from non-randomized studies of small numbers of people indicates no serious safety signals emerging for the use of tecovirimat in people with mpox infection, but a possible safety signal for brincidofovir. All three participants who received brincidofovir had raised alanine aminotransferase (ALT), but not bilirubin, suggesting mild liver injury. No study reported severe drug-induced liver injury with brincidofovir.

AUTHORS' CONCLUSIONS

Randomized controlled trials review This review found no evidence from randomized controlled trials concerning the efficacy and safety of therapeutics in humans with mpox. Non-randomized studies review Very low-certainty evidence from non-randomized studies indicates no serious safety signals emerging for the use of tecovirimat in people with mpox infection. In contrast, very low-certainty evidence raises a safety signal that brincidofovir may cause liver injury. This is also suggested by indirect evidence from brincidofovir use in smallpox. This warrants further investigation and monitoring. This Cochrane Review will be updated as new evidence becomes available to assist policymakers, health professionals, and consumers in making appropriate decisions for the treatment of mpox.

Oral Brincidofovir Therapy for Monkeypox Outbreak: A Focused Review on the Therapeutic Potential, Clinical Studies, Patent Literature, and Prospects

The monkeypox disease (MPX) outbreak of 2022 has been reported in more than one hundred countries and is becoming a global concern. Unfortunately, only a few treatments, such as tecovirimat (TCV), are available against MPX. Brincidofovir (BCV) is a United States Food and Drug Administration (USFDA)-approved antiviral against smallpox. This article reviews the potential of BCV for treating MPX and other Orthopoxvirus (OPXVs) diseases. The literature for this review was collected from PubMed, authentic websites (USFDA, Chimerix), and freely available patent databases (USPTO, Espacenet, and Patentscope). BCV (a lipophilic derivative of cidofovir) has been discovered and developed by Chimerix Incorporation, USA. Besides smallpox, BCV has also been tested clinically for various viral infections (adenovirus, cytomegalovirus, ebola virus, herpes simplex virus, and double-stranded DNA virus). Many health agencies and reports have recommended using BCV for MPX. However, no health agency has yet approved BCV for MPX. Accordingly, the off-label use of BCV is anticipated for MPX and various viral diseases. The patent literature revealed some important antiviral compositions of BCV. The authors believe there is a huge opportunity to create novel, inventive, and patentable BCV-based antiviral therapies (new combinations with existing antivirals) for OPXVs illnesses (MPX, smallpox, cowpox, camelpox, and vaccinia). It is also advised to conduct drug interaction (food, drug, and disease interaction) and drug resistance investigations on BCV while developing its combinations with other medications. The BCV-based drug repurposing options are also open for further exploration. BCV offers a promising opportunity for biosecurity against OPXV-based bioterrorism attacks and to control the MPX outbreak of 2022.

Therapeutic strategies for human poxvirus infections: Monkeypox (mpox), smallpox, molluscipox, and orf

Therapeutic and vaccine development for human poxvirus infections (e.g., monkeypox (mpox) virus, variola virus, molluscum contagiosum virus, orf virus) has been largely deserted, especially after the eradication of smallpox by 1980. Human mpox is a self-limited disease confined to Central and West Africa for decades. However, since April 2022, mpox has quickly emerged as a multi-country outbreak, urgently calling for effective antiviral agents and vaccines to control mpox. Here, this review highlights possible therapeutic options (e.g., tecovirimat, brincidofovir, cidofovir) and other strategies (e.g., vaccines, intravenous vaccinia immune globulin) for the management of human poxvirus infections worldwide.

Monkeypox in humans: a new outbreak

Infection caused by Monkeypox Virus (MPVX) has small rodents as its natural reservoir and both monkeys and humans are occasional hosts. The causative agent is an Orthopoxvirus (MPVX) that was isolated in monkeys in 1958 and proved capable of passing to humans in 1970. It remained contained in Africa, causing isolated episodes of infection, until 2003 when an outbreak occurred in the United States following importation of animals from that continent. Since then, anecdotal cases have continued to be reported outside Africa, usually very clearly linked to travelers to those countries, but in May 2022, a broad outbreak of this disease has begun, now affecting several continents, with the emergence of human cases of MPVX (H-MPVX) infection mainly among Men that have Sex with Men (MSM). The disease has an incubation time ranging from 5 to 15 days and is characterized by the presence of pustules, fever, malaise and headache. The presence of significant regional lymphadenopathy is a differential feature with episodes of classical smallpox. Proctitis and pharyngitis, with minimal skin lesions, may be another form of presentation. Diagnosis can be confirmed by PCR testing of lesions or by demonstration of MPVX in other body fluids or tissues, although in the appropriate epidemiologic setting the clinical picture is highly suggestive of the disease. Effective drug treatment has been developed as part of programs to protect against potential bioterrorist agents and smallpox vaccinees are known to have high protection against monkeypox. New vaccines are available, but neither the drugs nor the vaccines are yet freely available on the market. The prognosis of the disease appears, at least in adults in developed countries, to be good, with very low mortality figures and much less aggressive behavior than that described in classical smallpox. Isolation measures, essential for the control of the outbreak, have been published by the health authorities.

Prevention and Treatment of Monkeypox: A Systematic Review of Preclinical Studies

The outbreak of monkeypox, coupled with the onslaught of the COVID-19 pandemic is a critical communicable disease. This study aimed to systematically identify and review research done on preclinical studies focusing on the potential monkeypox treatment and immunization. The presented juxtaposition of efficacy of potential treatments and vaccination that had been tested in preclinical trials could serve as a useful primer of monkeypox virus. The literature identified using key terms such as monkeypox virus or management or vaccine stringed using Boolean operators was systematically reviewed. Pubmed, SCOPUS, Cochrane, and preprint databases were used, and screening was performed in accordance with PRISMA guidelines. A total of 467 results from registered databases and 116 from grey literature databases were screened. Of these results, 72 studies from registered databases and three grey literature studies underwent full-text screening for eligibility. In this systematic review, a total of 27 articles were eligible according to the inclusion criteria and were used. Tecovirimat, known as TPOXX or ST-246, is an antiviral drug indicated for smallpox infection whereas brincidofovir inhibits the viral DNA polymerase after incorporation into viral DNA. The ability of tecovirimat in providing protection to poxvirus-challenged animals from death had been demonstrated in a number of animal studies. Non-inferior with regard to immunogenicity was reported for the live smallpox/monkeypox vaccine compared with a single dose of a licensed live smallpox vaccine. The trial involving the live vaccine showed a geometric mean titre of vaccinia-neutralizing antibodies post two weeks of the second dose of the live smallpox/monkeypox vaccine. Of note, up to the third generation of smallpox vaccines-particularly JYNNEOS and Lc16m8-have been developed as preventive measures for MPXV infection and these vaccines had been demonstrated to have improved safety compared to the earlier generations.

First case report of human monkeypox in Latin America: The beginning of a new outbreak

On 13 May 2022, a familial cluster of two cases of monkeypox was reported in the United Kingdom (UK) by the UK Health Security Agency (UKHSA). These cases had no relation to a case imported from Nigeria that was previously reported on 7 May 2022 in the UK. In the following days, several other European Union (EU) the Member States and other countries have reported cases of monkeypox not linked to travel to endemic countries. The report by the World Health Organization (WHO) until May 26, 2022, is of a total of 257 confirmed cases and 120 suspected cases, without any report of death. This outbreak involves 23 countries that are not endemic to the monkeypox virus. Latin America had no reported cases. We describe a case of imported monkeypox in Mexico City, Mexico.

Poxviruses Bearing DNA Polymerase Mutations Show Complex Patterns of Cross-Resistance

Despite the eradication of smallpox four decades ago, poxviruses continue to be a threat to humans and animals. The arsenal of anti-poxvirus agents is very limited and understanding mechanisms of resistance to agents targeting viral DNA polymerases is fundamental for the development of antiviral therapies. We describe here the phenotypic and genotypic characterization of poxvirus DNA polymerase mutants isolated under selective pressure with different acyclic nucleoside phosphonates, including HPMPC (cidofovir), cHPMPC, HPMPA, cHPMPA, HPMPDAP, HPMPO-DAPy, and PMEO-DAPy, and the pyrophosphate analogue phosphonoacetic acid. Vaccinia virus (VACV) and cowpox virus drug-resistant viral clones emerging under drug pressure were characterized phenotypically (drug-susceptibility profile) and genotypically (DNA polymerase sequencing). Different amino acid changes in the polymerase domain and in the 3′-5′ exonuclease domain were linked to drug resistance. Changes in the 3′-5′ domain emerged earlier than in the polymerase domain when viruses acquired a combination of mutations. Our study highlights the importance of poxvirus DNA polymerase residues 314, 613, 684, 688, and 851, previously linked to drug resistance, and identified several novel mutations in the 3′-5′ exonuclease domain (M313I, F354L, D480Y) and in the DNA polymerase domain (A632T, T831I, E856K, L924F) associated with different drug-susceptibility profiles. Furthermore, a combination of mutations resulted in complex patterns of cross-resistance. Modeling of the VACV DNA polymerase bearing the newly described mutations was performed to understand the effects of these mutations on the structure of the viral enzyme. We demonstrated the emergence of drug-resistant DNA polymerase mutations in complex patterns to be considered in case such mutations should eventually arise in the clinic.

Pharmacokinetics and Efficacy of a Potential Smallpox Therapeutic, Brincidofovir, in a Lethal Monkeypox Virus Animal Model

Smallpox, caused by Variola virus (VARV), was eradicated in 1980; however, VARV bioterrorist threats still exist, necessitating readily available therapeutics. Current preparedness activities recognize the importance of oral antivirals and recommend therapeutics with different mechanisms of action. Monkeypox virus (MPXV) is closely related to VARV, causing a highly similar clinical human disease, and can be used as a surrogate for smallpox antiviral testing. The prairie dog MPXV model has been characterized and used to study the efficacy of antipoxvirus therapeutics, including recently approved TPOXX (tecovirimat). Brincidofovir (BCV; CMX001) has shown antiviral activity against double-stranded DNA viruses, including poxviruses. To determine the exposure of BCV following oral administration to prairie dogs, a pharmacokinetics (PK) study was performed. Analysis of BCV plasma concentrations indicated variability, conceivably due to the outbred nature of the animals. To determine BCV efficacy in the MPXV prairie dog model, groups of animals were intranasally challenged with 9 × 10⁵ plaque-forming units (PFU; 90% lethal dose [LD₉₀]) of MPXV on inoculation day 0 (ID0). Animals were divided into groups based on the first day of BCV treatment relative to inoculation day (ID-1, ID0, or ID1). A trend in efficacy was noted dependent upon treatment initiation (57% on ID-1, 43% on ID0, and 29% on ID1) but was lower than demonstrated in other animal models. Analysis of the PK data indicated that BCV plasma exposure (maximum concentration [C _max]) and the time of the last quantifiable concentration (AUC_last) were lower than in other animal models administered the same doses, indicating that suboptimal BCV exposure may explain the lower protective effect on survival.IMPORTANCE Preparedness activities against highly transmissible viruses with high mortality rates have been highlighted during the ongoing coronavirus disease 2019 (COVID-19) pandemic. Smallpox, caused by variola virus (VARV) infection, is highly transmissible, with an estimated 30% mortality. Through an intensive vaccination campaign, smallpox was declared eradicated in 1980, and routine smallpox vaccination of individuals ceased. Today's current population has little/no immunity against VARV. If smallpox were to reemerge, the worldwide results would be devastating. Recent FDA approval of one smallpox antiviral (tecovirimat) was a successful step in biothreat preparedness; however, orthopoxviruses can become resistant to treatment, suggesting the need for multiple therapeutics. Our paper details the efficacy of the investigational smallpox drug brincidofovir in a monkeypox virus (MPXV) animal model. Since brincidofovir has not been tested in vivo against smallpox, studies with the related virus MPXV are critical in understanding whether it would be protective in the event of a smallpox outbreak.

IMVAMUNE® and ACAM2000® Provide Different Protection against Disease When Administered Postexposure in an Intranasal Monkeypox Challenge Prairie Dog Model

The protection provided by smallpox vaccines when used after exposure to Orthopoxviruses is poorly understood. Postexposu re administration of 1st generation smallpox vaccines was effective during eradication. However, historical epidemiological reports and animal studies on postexposure vaccination are difficult to extrapolate to today’s populations, and 2nd and 3rd generation vaccines, developed after eradication, have not been widely tested in postexposure vaccination scenarios. In addition to concerns about preparedness for a potential malevolent reintroduction of variola virus, humans are becoming increasingly exposed to naturally occurring zoonotic orthopoxviruses and, following these exposures, disease severity is worse in individuals who never received smallpox vaccination. This study investigated whether postexposure vaccination of prairie dogs with 2nd and 3rd generation smallpox vaccines was protective against monkeypox disease in four exposure scenarios. We infected animals with monkeypox virus at doses of 10⁴ pfu (2× LD₅₀) or 10⁶ pfu (170× LD₅₀) and vaccinated the animals with IMVAMUNE^® or ACAM2000^® either 1 or 3 days after challenge. Our results indicated that postexposure vaccination protected the animals to some degree from the 2× LD₅₀, but not the 170× LD₅ challenge. In the 2× LD₅₀ challenge, we also observed that administration of vaccine at 1 day was more effective than administration at 3 days postexposure for IMVAMUNE^®, but ACAM2000^® was similarly effective at either postexposure vaccination time-point. The effects of postexposure vaccination and correlations with survival of total and neutralizing antibody responses, protein targets, take formation, weight loss, rash burden, and viral DNA are also presented.

Field Trial Vaccination against Cowpox in Two Alpaca Herds

In Europe, cowpox virus (CPXV) infection in South American camelids occurs as a so-called spill-over infection. Although infected animals generally have a mild form of the disease and survive, cases of fatal generalised CPXV infection have also been described. Prevention by prophylactic vaccination is the only way to protect animals from disease. In the present study, modified vaccinia virus Ankara (MVA) vaccine, which has been successfully used in many animal species, was used in a prime-boost vaccination regimen in two alpaca herds with a history of CPXV infection. The focus of the study was the prevention of further clinical cases, and to determine the safety and immunogenicity of the MVA vaccine in alpacas. The MVA vaccine was well tolerated and safe in the 94 animals vaccinated. An indirect immunofluorescence assay (IFA) using MVA as an antigen showed that the seroprevalence of antibody after booster vaccination was 81.3% in herd I and 91.7% in herd II. Detectable antibody titres declined to 15.6% in herd I and 45.8% in herd II over a 12-month period after booster vaccination. Animals could be divided into four groups based on individual antibody titres determined over one year: Group 1 consisted of 19.3% of animals that were seropositive until the end of the trial period; Group 2 consisted of 58.0% of animals that were seropositive after booster vaccination, but seronegative one year later; Group 3 consisted of 14.7% of animals that were not seropositive at any time point; and Group 4 consisted of 7.9% of animals that were seropositive after initial immunisation, seronegative six months later, but seropositive or intermediate in IFA one year after immunisation, likely because of natural exposure. In new-born crias born to MVA-vaccinated mares, specific maternal antibodies were detected in 50.0% of animals up to 14 weeks of age. Our results confirm that MVA vaccination is a feasible tool for the prevention of CPXV disease in alpacas. Long-term studies are needed to verify future vaccination regimen in CPXV affected herds.

Antivirals in medical biodefense

The viruses historically implicated or currently considered as candidates for misuse in bioterrorist events are poxviruses, filoviruses, bunyaviruses, orthomyxoviruses, paramyxoviruses and a number of arboviruses causing encephalitis, including alpha- and flaviviruses. All these viruses are of concern for public health services when they occur in natural outbreaks or emerge in unvaccinated populations. Recent events and intelligence reports point to a growing risk of dangerous biological agents being used for nefarious purposes. Public health responses effective in natural outbreaks of infectious disease may not be sufficient to deal with the severe consequences of a deliberate release of such agents. One important aspect of countermeasures against viral biothreat agents are the antiviral treatment options available for use in post-exposure prophylaxis. These issues were adressed by the organizers of the 16th Medical Biodefense Conference, held in Munich in 2018, in a special session on the development of drugs to treat infections with viruses currently perceived as a threat to societies or associated with a potential for misuse as biothreat agents. This review will outline the state-of-the-art methods in antivirals research discussed and provide an overview of antiviral compounds in the pipeline that are already approved for use or still under development.