Recent advances in the study of live attenuated cell-cultured smallpox vaccine LC16m8

Potential use of cidofovir, brincidofovir, and tecovirimat drugs in fighting monkeypox infection: recent trends and advancements

Recent years have witnessed the rise of more recent pandemic outbreaks including COVID-19 and monkeypox. A multinational monkeypox outbreak creates a complex situation that necessitates countermeasures to the existing quo. The first incidence of monkeypox was documented in the 1970s, and further outbreaks led to a public health emergency of international concern. Yet as of right now, neither vaccines nor medicines are certain to treat monkeypox. Even the inability of conducting human clinical trials has prevented thousands of patients from receiving effective disease management. The current state of the disease's understanding, the treatment options available, financial resources, and lastly international policies to control an epidemic state are the major obstacles to controlling epidemics. The current review focuses on the epidemiology of monkeypox, scientific ideas, and available treatments, including potential monkeypox therapeutic methods. As a result, a thorough understanding of monkeypox literature will facilitate in the development of new therapeutic medications for the prevention and treatment of monkeypox.

Concurrent Clade I and Clade II Monkeypox Virus Circulation, Cameroon, 1979-2022

During 1979-2022, Cameroon recorded 32 laboratory-confirmed mpox cases among 137 suspected mpox cases identified by the national surveillance network. The highest positivity rate occurred in 2022, indicating potential mpox re-emergence in Cameroon. Both clade I (n = 12) and clade II (n = 18) monkeypox virus (MPXV) were reported, a unique feature of mpox in Cameroon. The overall case-fatality ratio of 2.2% was associated with clade II. We found mpox occurred only in the forested southern part of the country, and MPXV phylogeographic structure revealed a clear geographic separation among concurrent circulating clades. Clade I originated from eastern regions close to neighboring mpox-endemic countries in Central Africa; clade II was prevalent in western regions close to West Africa. Our findings suggest that MPXV re-emerged after a 30-year lapse and might arise from different viral reservoirs unique to ecosystems in eastern and western rainforests of Cameroon.

Progress and prospects on vaccine development against Monkeypox Infection

The monkeypox virus (MPOX) is an uncommon zoonotic illness brought on by an orthopoxvirus (OPXV). MPOX can occur with symptoms similar to smallpox. Since April 25, 2023, 110 nations have reported 87,113 confirmed cases and 111 fatalities. Moreover, the outspread prevalence of MPOX in Africa and a current outbreak of MPOX in the U.S. have made it clear that naturally occurring zoonotic OPXV infections remain a public health concern. Existing vaccines, though they provide cross-protection to MPOX, are not specific for the causative virus, and their effectiveness in the light of the current multi-country outbreak is still to be verified. Furthermore, as a sequel of the eradication and cessation of smallpox vaccination for four decades, MPOX found a possibility to re-emerge, but with distinct characteristics. The World Health Organization (WHO) suggested that nations use affordable MPOX vaccines within a framework of coordinated clinical effectiveness and safety evaluations. Vaccines administered in the smallpox control program and conferred immunity against MPOX. Currently, vaccines approved by WHO for use against MPOX are replicating (ACAM2000), low replicating (LC16m8), and non-replicating (MVA-BN). Although vaccines are accessible, investigations have demonstrated that smallpox vaccination is approximately 85% efficient in inhibiting MPOX. In addition, developing new vaccine methods against MPOX can help prevent this infection. To recognize the most efficient vaccine, it is essential to assess effects, including reactogenicity, safety, cytotoxicity effect, and vaccine-associated side effects, especially for high-risk and vulnerable people. Recently, several orthopoxvirus vaccines have been produced and are being evaluated. Hence, this review aims to provide an overview of the efforts dedicated to several types of vaccine candidates with different strategies for MPOX, including inactivated, live-attenuated, virus-like particles (VLPs), recombinant protein, nucleic acid, and nanoparticle-based vaccines, which are being developed and launched.

Vaccines against monkeypox

The monkeypox virus is a virus that has 90% genomic homology with the human (smallpox), but it is naturally transmitted between different wild animal reservoirs and is considered a zoonosis. Throughout the 20th century, different vaccines based on the vaccinia poxvirus were developed and used for vaccination against smallpox. After the eradication of smallpox, these vaccines were no longer used. Current vaccines against monkeypox virus are classified by the WHO as replicative (ACAM2000), minimally replicative (LC16m8) and non-replicative (MVA-BN), the latter being the one currently used. The 2022 extra-African monkeypox virus epidemic has highlighted the lack of vaccines with proven efficacy and low reactogenicity. It is considered that the use of this vaccine in the current outbreak may play a role in the prevention or attenuation of the disease as pre-exposure prophylaxis in close contacts of confirmed cases.

Vaccines against monkeypox

The monkeypox virus is a virus that has 90% genomic homology with the human (smallpox), but it is naturally transmitted between different wild animal reservoirs and is considered a zoonosis. Throughout the 20th century, different vaccines based on the vaccinia poxvirus were developed and used for vaccination against smallpox. After the eradication of smallpox, these vaccines were no longer used. Current vaccines against monkeypox virus are classified by the WHO as replicative (ACAM2000), minimally replicative (LC16m8) and non-replicative (MVA-BN), the latter being the one currently used. The 2022 extra-African monkeypox virus epidemic has highlighted the lack of vaccines with proven efficacy and low reactogenicity. It is considered that the use of this vaccine in the current outbreak may play a role in the prevention or attenuation of the disease as pre-exposure prophylaxis in close contacts of confirmed cases.

Smallpox, Monkeypox and Other Human Orthopoxvirus Infections

Considering that vaccination against smallpox with live vaccinia virus led to serious adverse effects in some cases, the WHO, after declaration of the global eradication of smallpox in 1980, strongly recommended to discontinue the vaccination in all countries. This led to the loss of immunity against not only smallpox but also other zoonotic orthopoxvirus infections in humans over the past years. An increasing number of human infections with zoonotic orthopoxviruses and, first of all, monkeypox, force us to reconsider a possible re-emergence of smallpox or a similar disease as a result of natural evolution of these viruses. The review contains a brief analysis of the results of studies on genomic organization and evolution of human pathogenic orthopoxviruses, development of modern methods for diagnosis, vaccination, and chemotherapy of smallpox, monkeypox, and other zoonotic human orthopoxvirus infections.

Outbreaks of human monkeypox during the COVID-19 pandemic: a systematic review for healthcare professionals

The ongoing 2022 multicountry monkeypox epidemic has drawn worldwide attention. Human monkeypox is a virus that spreads from animals to humans. It is an endemic disease in the rain forests of Central and West Africa. However, the disease recently emerged in India, and also in United States through imported wild rodents from Africa, even though the world is still struggling to escape from the clutches of the COVID-19 pandemic. Monkeypox is one of the contagious zoonotic diseases caused by the monkeypox virus (MPXV), transmitted to humans by direct contact with an infected person or animal or contact with virus-contaminated material. Its lesions are similar to smallpox in humans with various medical complications including flu-like symptoms, fever, malaise, back pain, headache, and a characteristic rash. Public health experts around the world are very concerned about the rapid spread of the infection, which has intensified efforts to find the source and cause of this phenomenon. Several viral infections with epidemic potential threaten global health security. Early recognition of cases and timely intervention of potential transmission chains are necessary to contain further outbreaks. At this early stage of monkeypox outbreaks, the current review provides updated information on the current worldwide monkeypox outbreak status, disease aetiology, clinical presentation, therapy, and preventive measures worldwide. Our review will also provide useful information to health professionals and the general public.

Prevention of monkeypox with vaccines: a rapid review

The largest outbreak of monkeypox in history began in May, 2022, and has rapidly spread across the globe ever since. The purpose of this Review is to briefly describe human immune responses to orthopoxviruses; provide an overview of the vaccines available to combat this outbreak; and discuss the various clinical data and animal studies evaluating protective immunity to monkeypox elicited by vaccinia virus-based smallpox vaccines, address ongoing concerns regarding the outbreak, and provide suggestions for the appropriate use of vaccines as an outbreak control measure. Data showing clinical effectiveness (~85%) of smallpox vaccines against monkeypox come from surveillance studies conducted in central Africa in the 1980s and later during outbreaks in the same area. These data are supported by a large number of animal studies (primarily in non-human primates) with live virus challenge by various inoculation routes. These studies uniformly showed a high degree of protection and immunity against monkeypox virus following vaccination with various smallpox vaccines. Smallpox vaccines represent an effective countermeasure that can be used to control monkeypox outbreaks. However, smallpox vaccines do cause side-effects and the replication-competent, second-generation vaccines have contraindications. Third-generation vaccines, although safer for use in immunocompromised populations, require two doses, which is an impediment to rapid outbreak response. Lessons learned from the COVID-19 pandemic should be used to inform our collective response to this monkeypox outbreak and to future outbreaks.

Animal Models Used in Monkeypox Research

Monkeypox is an emerging zoonotic disease with a growing prevalence outside of its endemic area, posing a significant threat to public health. Despite the epidemiological and field investigations of monkeypox, little is known about its maintenance in natural reservoirs, biological implications or disease management. African rodents are considered possible reservoirs, although many mammalian species have been naturally infected with the monkeypox virus (MPXV). The involvement of domestic livestock and pets in spillover events cannot be ruled out, which may facilitate secondary virus transmission to humans. Investigation of MPXV infection in putative reservoir species and non-human primates experimentally uncovered novel findings relevant to the course of pathogenesis, virulence factors and transmission of MPXV that provided valuable information for designing appropriate prevention measures and effective vaccines.

Monkeypox: epidemiology, pathogenesis, treatment and prevention

Monkeypox is a zoonotic disease that was once endemic in west and central Africa caused by monkeypox virus. However, cases recently have been confirmed in many nonendemic countries outside of Africa. WHO declared the ongoing monkeypox outbreak to be a public health emergency of international concern on July 23, 2022, in the context of the COVID-19 pandemic. The rapidly increasing number of confirmed cases could pose a threat to the international community. Here, we review the epidemiology of monkeypox, monkeypox virus reservoirs, novel transmission patterns, mutations and mechanisms of viral infection, clinical characteristics, laboratory diagnosis and treatment measures. In addition, strategies for the prevention, such as vaccination of smallpox vaccine, is also included. Current epidemiological data indicate that high frequency of human-to-human transmission could lead to further outbreaks, especially among men who have sex with men. The development of antiviral drugs and vaccines against monkeypox virus is urgently needed, despite some therapeutic effects of currently used drugs in the clinic. We provide useful information to improve the understanding of monkeypox virus and give guidance for the government and relative agency to prevent and control the further spread of monkeypox virus.

A replication-competent smallpox vaccine LC16m8Δ-based COVID-19 vaccine

Viral vectors are a potent vaccine platform for inducing humoral and T-cell immune responses. Among the various viral vectors, replication-competent ones are less commonly used for coronavirus disease 2019 (COVID-19) vaccine development compared with replication-deficient ones. Here, we show the availability of a smallpox vaccine LC16m8Δ (m8Δ) as a replication-competent viral vector for a COVID-19 vaccine. M8Δ is a genetically stable variant of the licensed and highly effective Japanese smallpox vaccine LC16m8. Here, we generated two m8Δ recombinants: one harbouring a gene cassette encoding the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike (S) glycoprotein, named m8Δ-SARS2(P7.5-S)-HA; and one encoding the S protein with a highly polybasic motif at the S1/S2 cleavage site, named m8Δ-SARS2(P7.5-S_HN)-HA. M8Δ-SARS2(P7.5-S)-HA induced S-specific antibodies in mice that persisted for at least six weeks after a homologous boost immunization. All eight analysed serum samples displayed neutralizing activity against an S-pseudotyped virus at a level similar to that of serum samples from patients with COVID-19, and more than half (5/8) also had neutralizing activity against the Delta/B.1.617.2 variant of concern. Importantly, most serum samples also neutralized the infectious SARS-CoV-2 Wuhan and Delta/B.1.617.2 strains. In contrast, immunization with m8Δ-SARS2(P7.5-S_HN)-HA elicited significantly lower antibody titres, and the induced antibodies had less neutralizing activity. Regarding T-cell immunity, both m8Δ recombinants elicited S-specific multifunctional CD8⁺ and CD4⁺ T-cell responses even after just a primary immunization. Thus, m8Δ provides an alternative method for developing a novel COVID-19 vaccine.

Genome stability of the vaccine strain VAC∆6

Due to cessation of mass smallpox vaccination in 1980, the collective immunity of humans against orthopoxvirus infections has virtually been lost. Therefore, the risk of spreading zoonotic human orthopoxvirus infections caused by monkeypox and cowpox viruses has increased in the world. First-generation smallpox vaccines based on Vaccinia virus (VAC) are reactogenic and therefore not suitable for mass vaccination under current conditions. This necessitates the development of modern safe live vaccines based on VAC using genetic engineering. We created the VACΔ6 strain by transient dominant selection. In the VACΔ6 genome, f ive virulence genes were intentionally deleted, and one gene was inactivated by inserting a synthetic DNA fragment. The virus was passaged 71 times in CV-1 cells to obtain the VACΔ6 strain from the VAC LIVP clonal variant. Such a long passage history might have led to additional off-target mutations in VACΔ6 compared to the original LIVP variant. To prevent this, we performed a genome-wide sequencing of VAC LIVP, VACΔ6, and f ive intermediate viral strains to assess possible off-target mutations. A comparative analysis of complete viral genomes showed that, in addition to target mutations, only two nucleotide substitutions occurred spontaneously when obtaining VACΔ4 from the VACΔ3 strain; the mutations persisting in the VACΔ5 and VACΔ6 genomes. Both nucleotide substitutions are located in intergenic regions (positions 1431 and 189738 relative to LIVP), which indicates an extremely rare occurrence of off-target mutations when using transient dominant selection to obtain recombinant VAC variants with multiple insertions/deletions. To assess the genome stability of the resulting attenuated vaccine strain, 15 consecutive cycles of cultivation of the industrial VACΔ6 strain were performed in 4647 cells certif ied for vaccine production in accordance with the “Guidelines for Clinical Trials of Medicinal Products”. PCR and sequencing analysis of six DNA fragments corresponding to the regions of disrupted genes in VACΔ6 showed that all viral DNA sequences remained unchanged after 15 passages in 4647 cells.

Effect of Serial Passage on the Pathogenicity and Immunogenicity of Vaccinia Virus LC16m8 Strain

The phenotype of an attenuated live vaccine depends on gene mutation achieved by, for example, many passages in cultured cells. Viral clones with preferable phenotypes are selected and the causative genetic mutation(s) are later identified. LC16m8 is an example of a highly attenuated smallpox vaccine that was developed and licensed in Japan in the 1970s. LC16m8 was obtained by the passaging of Lister strain, with indicators of small plaque formation and temperature sensitivity as virus phenotypes. This strain can replicate in mammalian cells and provides robust cellular and humoral immunity, as well as long-term immune memory. Recent studies using proteome-wide antigen arrays have revealed that antibody production against LC16m8 and other VACVs differs largely among individuals. Moreover, associations between SNPs in immune-related genes and immune outcomes have been increasingly found. These results lead to predicting adverse events of a vaccine, which is a purpose of vaccinomics. Studies on VACV will continue to contribute to the understanding of host-pathogen interactions and to development of a vaccine for other infectious and non-infectious diseases. Here, we review studies of VACV, including our recent research on LC16m8, with a focus on the phenotype and genotype, and we discuss future research directions.

Development of an attenuated smallpox vaccine candidate: The KVAC103 strain

Smallpox, a disease caused by the variola virus, is one of the most dangerous diseases and had killed numerous people before it was eradicated in 1980. However, smallpox has emerged as the most threatening bio-terrorism agent; as the first- and second-generation smallpox vaccines have been controversial and have caused severe adverse reactions, new demands for safe smallpox vaccines have been raised and some attenuated smallpox vaccines have been developed. We have developed a cell culture-based highly attenuated third-generation smallpox vaccine candidate KVAC103 strain by 103 serial passages of the Lancy-Vaxina strain derived from the Lister in Vero cells. Several clones were selected, taking into consideration their shape, size, and growth rate in mammalian cells. The clones were then inoculated intracerebrally in suckling mice to test for neurovirulence by observing survival. Protective immune responses in adult mice were examined by measuring the levels of neutralization antibodies and IFN-γ expression. Among several clones, clone 7 was considered the best alternative candidate because there was no mortality in suckling mice against a lethal challenge. In addition, enhanced neutralizing antibodies and T-cell mediated IFN-γ production were observed in clone 7-immunized mice. Clone 7 was named "KVAC103" and was used for the skin toxicity test and full-genome analysis. KVAC103-inoculated rabbits showed reduced skin lesions compared to those inoculated with the Lister strain, Lancy-Vaxina. A whole genome analysis of KVAC103 revealed two major deleted regions that might contribute to the reduced virulence of KVAC103 compared to the Lister strain. Phylogenetic inference supported the close relationship with the Lister strain. Collectively, our data demonstrate that KVAC103 holds promise for use as a third-generation smallpox vaccine strain due to its enhanced safety and efficacy.

[We should be prepared to smallpox re-emergence.]

The review contains a brief analysis of the results of investigations conducted during 40 years after smallpox eradication and directed to study genomic organization and evolution of variola virus (VARV) and development of modern diagnostics, vaccines and chemotherapies of smallpox and other zoonotic orthopoxviral infections of humans. Taking into account that smallpox vaccination in several cases had adverse side effects, WHO recommended ceasing this vaccination after 1980 in all countries of the world. The result of this decision is that the mankind lost the collective immunity not only to smallpox, but also to other zoonotic orthopoxvirus infections. The ever more frequently recorded human cases of zoonotic orthopoxvirus infections force to renew consideration of the problem of possible smallpox reemergence resulting from natural evolution of these viruses. Analysis of the available archive data on smallpox epidemics, the history of ancient civilizations, and the newest data on the evolutionary relationship of orthopoxviruses has allowed us to hypothesize that VARV could have repeatedly reemerged via evolutionary changes in a zoonotic ancestor virus and then disappeared because of insufficient population size of isolated ancient civilizations. Only the historically last smallpox pandemic continued for a long time and was contained and stopped in the 20th century thanks to the joint efforts of medics and scientists from many countries under the aegis of WHO. Thus, there is no fundamental prohibition on potential reemergence of smallpox or a similar human disease in future in the course of natural evolution of the currently existing zoonotic orthopoxviruses. Correspondingly, it is of the utmost importance to develop and widely adopt state-of-the-art methods for efficient and rapid species-specific diagnosis of all orthopoxvirus species pathogenic for humans, VARV included. It is also most important to develop new safe methods for prevention and therapy of human orthopoxvirus infections.

Profiling of the antibody response to attenuated LC16m8 smallpox vaccine using protein array analysis

Concerns about bioterrorism and outbreaks of zoonotic orthopoxvirus require safe and efficacious smallpox vaccines. We previously reported the clinical efficacy and safety profiles of LC16m8, a live, attenuated, cell culture-derived, smallpox vaccine, examined in over 3000 healthy Japanese adults with various vaccination histories. In this study, serum of approximately 200 subjects pre and post LC16m8 vaccination were subjected to a vaccinia virus-specific protein array to evaluate the proteome-wide immunogenicity. The relationships between antigen-specific antibodies and plaque reduction neutralization titers were analyzed. LC16m8 induced antibodies to multiple vaccinia antigens in primary-vaccinated individuals and yielded effective booster responses in previously vaccinated individuals, demonstrating similar antibody profiles to those reported for other vaccinia virus strains. Several immunodominant antigens were indicated to be important for neutralization of the intracellular mature virion. The similarity of antibody profiles between LC16m8 and other smallpox vaccine strains supports the immunogenicity and protective efficacy of LC16m8.

A Critical Analysis of the Scientific and Commercial Rationales for the De Novo Synthesis of Horsepox Virus

This article evaluates the scientific and commercial rationales for the synthesis of horsepox virus. I find that the claimed benefits of using horsepox virus as a smallpox vaccine rest on a weak scientific foundation and an even weaker business case that this project will lead to a licensed medical countermeasure. The combination of questionable benefits and known risks of this dual use research raises serious questions about the wisdom of undertaking research that could be used to recreate variola virus. This analysis also raises important questions about the propriety of a private company sponsoring such dual use research without appropriate oversight and highlights an important gap in United States dual use research regulations.

Challenges and Achievements in Prevention and Treatment of Smallpox

Declaration of smallpox eradication by the WHO in 1980 led to discontinuation of the worldwide vaccination campaign. The increasing percentage of unvaccinated individuals, the existence of its causative infectious agent variola virus (VARV), and the recent synthetic achievements increase the threat of intentional or accidental release and reemergence of smallpox. Control of smallpox would require an emergency vaccination campaign, as no other protective measure has been approved to achieve eradication and ensure worldwide protection. Experimental data in surrogate animal models support the assumption, based on anecdotal, uncontrolled historical data, that vaccination up to 4 days postexposure confers effective protection. The long incubation period, and the uncertainty of the exposure status in the surrounding population, call for the development and evaluation of safe and effective methods enabling extension of the therapeutic window, and to reduce the disease manifestations and vaccine adverse reactions. To achieve these goals, we need to evaluate the efficacy of novel and already licensed vaccines as a sole treatment, or in conjunction with immune modulators and antiviral drugs. In this review, we address the available data, recent achievements, and open questions.

Protection of Mice from Lethal Vaccinia Virus Infection by Vaccinia Virus Protein Subunits with a CpG Adjuvant

Smallpox vaccination carries a high risk of adverse events in recipients with a variety of contra-indications for live vaccines. Although alternative non-replicating vaccines have been described in the form of replication-deficient vaccine viruses, DNA vaccines, and subunit vaccines, these are less efficacious than replicating vaccines in animal models. DNA and subunit vaccines in particular have not been shown to give equivalent protection to the traditional replicating smallpox vaccine. We show here that combinations of the orthopoxvirus A27, A33, B5 and L1 proteins give differing levels of protection when administered in different combinations with different adjuvants. In particular, the combination of B5 and A27 proteins adjuvanted with CpG oligodeoxynucleotides (ODN) gives a level of protection in mice that is equivalent to the Lister traditional vaccine in a lethal vaccinia virus challenge model.

40 Years without Smallpox

The last case of natural smallpox was recorded in October, 1977. It took humanity almost 20 years to achieve that feat after the World Health Organization had approved the global smallpox eradication program. Vaccination against smallpox was abolished, and, during the past 40 years, the human population has managed to lose immunity not only to smallpox, but to other zoonotic orthopoxvirus infections as well. As a result, multiple outbreaks of orthopoxvirus infections in humans in several continents have been reported over the past decades. The threat of smallpox reemergence as a result of evolutionary transformations of these zoonotic orthopoxviruses exists. Modern techniques for the diagnostics, prevention, and therapy of smallpox and other orthopoxvirus infections are being developed today.

Are We Prepared in Case of a Possible Smallpox-Like Disease Emergence?

Smallpox was the first human disease to be eradicated, through a concerted vaccination campaign led by the World Health Organization. Since its eradication, routine vaccination against smallpox has ceased, leaving the world population susceptible to disease caused by orthopoxviruses. In recent decades, reports of human disease from zoonotic orthopoxviruses have increased. Furthermore, multiple reports of newly identified poxviruses capable of causing human disease have occurred. These facts raise concerns regarding both the opportunity for these zoonotic orthopoxviruses to evolve and become a more severe public health issue, as well as the risk of Variola virus (the causative agent of smallpox) to be utilized as a bioterrorist weapon. The eradication of smallpox occurred prior to the development of the majority of modern virological and molecular biological techniques. Therefore, there is a considerable amount that is not understood regarding how this solely human pathogen interacts with its host. This paper briefly recounts the history and current status of diagnostic tools, vaccines, and anti-viral therapeutics for treatment of smallpox disease. The authors discuss the importance of further research to prepare the global community should a smallpox-like virus emerge.

Comparative Efficacy of Intramuscular and Scarification Routes of Administration of Live Smallpox Vaccine in a Murine Challenge Model

In recent years concern has mounted regarding the possibility of a re-emergence of smallpox through biowarfare or bioterrorism. There is also concern over the incidence of human monkeypox in endemic areas and the potential for monkeypox to be accidentally transported to non-endemic areas. In the event of re-emergence of smallpox or emergence of monkeypox, the accepted route of administration for live replicating smallpox vaccine is dermal scarification, which generates a virus-shedding lesion that persists for several days at the vaccination site. The lesion is a potential source of contact transmission of vaccine to individuals who may be contra-indicated for receipt of the live vaccine. In this study, we compare dermal scarification with intramuscular vaccination for replicating smallpox vaccine in a mouse lethal challenge model. Comparisons are made over multiple vaccine and challenge doses and data recorded for lethality, disease severity, and antibody responses. Qualitative and quantitative differences between the two routes are observed, and for the intramuscular route the febrile response is not suppressed after subsequent virulent vaccinia virus challenge. However both routes generate an immune response and protect from severe disease and death. Although dermal scarification is the preferred route of vaccination for the general population, intramuscular vaccination may be an option for people who are not contraindicated for the live vaccine, but who are close contacts of people who are contraindicated for the live vaccine, in an emergency situation.