Efficacy and Safety of the Smallpox Vaccine for Postexposure Prophylaxis in Monkeypox: Protocol for an Open-Labeled, Single-Armed Study

BACKGROUND

In May 2022, a case of monkeypox (currently known as "mpox") with no history of overseas travel was reported in the United Kingdom, followed by reports of infections reported in Europe, the United States, and other countries worldwide. Due to the significant overlap in immune responses among viruses of the genus Orthopoxvirus (including smallpox virus, mpox virus, and vaccinia virus), it is believed that cross-immunity can be achieved by administering the smallpox virus vaccine. In Japan, a smallpox vaccine (LC16m8 strain vaccine) has been approved; however, there was no regulatory approval for the mpox vaccine during the design of this study. Although it is believed that individuals exposed to the mpox virus may receive smallpox vaccination as mpox prophylaxis, the existing evidence is not clear.

OBJECTIVE

The primary objective was to evaluate the efficacy of the LC16m8 strain vaccine, approved for smallpox in Japan, for postexposure prophylaxis against mpox when administered to close contacts of individuals with mpox. The secondary objective was to investigate the safety of the vaccine for postexposure prophylaxis against mpox.

METHODS

The study aimed to enroll 100 vaccinated participants who had been identified as close contacts of individuals with mpox. Consent was obtained, and the participants are inoculated with the vaccine. Daily recordings of symptoms (body temperature, headache, rash, and side effects) were made until day 21 and then again on day 28. Furthermore, additional evaluations of adverse events were performed by the investigators on days 7, 14, 21, and 28. Considering that the maximum incubation period for mpox is 21 days, the primary end point is the presence or absence of the disease 21 days after close contact. The primary analysis focused on cases within 4 days of intense contact as it has been reported that vaccination within this timeframe can reduce the incidence of the disease.

RESULTS

The first trial participant was enrolled on July 28, 2022, and the research period concluded in March 2023. The study results will be published in a peer-reviewed scientific journal.

CONCLUSIONS

This study allowed us to investigate the efficacy and safety of the LC16m8 strain vaccine in postexposure prophylaxis against mpox.

TRIAL REGISTRATION

Japan Registry of Clinical Trials jRCTs031220137; https://jrct.niph.go.jp/en-latest-detail/jRCTs031220137.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/46955.

Belarusian Healthcare Professionals' Views on Monkeypox and Vaccine Hesitancy

BACKGROUND

Despite the low transmission risk of Monkeypox (mpox) in Belarus, this study is vital as it contributes to our understanding of vaccine hesitancy among healthcare professionals (HCPs). It aims to assess vaccination perceptions and evaluate the willingness to pay for the vaccine among Belarusian HCPs, thereby enhancing pandemic preparedness.

METHODS

in October 2022, a cross-sectional survey-based study was conducted among Belarusian HCPs using a self-administered questionnaire (SAQ). Invitations were disseminated via social media platforms using a snowball sampling method. The SAQ encompassed various categories, including sociodemographic details, medical history, sources of mpox information, perceived and factual mpox knowledge, and perceptions of the mpox vaccine according to the health belief model (HBM), mpox vaccine acceptance and willingness to pay (WTP).

RESULTS

while a large proportion of respondents had good knowledge of mpox epidemiology and its clinical manifestations, their awareness of available vaccines and treatment options was limited. Consequently, a significant correlation was found between the history of influenza vaccination and mpox-related knowledge. Furthermore, the study showed that just over half of the participants (51.4%) were willing to receive the mpox vaccine if offered for free, safely, and effectively, with their decision largely influenced by perceived benefits (Spearman's rho = 0.451) and cues to action (Spearman's rho = 0.349). However, a considerable degree of hesitancy (30.6%) and resistance (18.1%) towards the mpox vaccine was observed, underscoring the need for targeted interventions to address these issues.

CONCLUSIONS

this study highlights a significant knowledge gap among Belarusian HCPs about mpox vaccines and treatments, despite a general awareness of the disease's epidemiology and symptoms, and it underscores the need for targeted interventions to enhance mpox knowledge and vaccine acceptance.

Virus-specific and shared gene expression signatures in immune cells after vaccination in response to influenza and vaccinia stimulation

Background

In the vaccine era, individuals receive multiple vaccines in their lifetime. Host gene expression in response to antigenic stimulation is usually virus-specific; however, identifying shared pathways of host response across a wide spectrum of vaccine pathogens can shed light on the molecular mechanisms/components which can be targeted for the development of broad/universal therapeutics and vaccines.

Method

We isolated PBMCs, monocytes, B cells, and CD8+ T cells from the peripheral blood of healthy donors, who received both seasonal influenza vaccine (within <1 year) and smallpox vaccine (within 1 - 4 years). Each of the purified cell populations was stimulated with either influenza virus or vaccinia virus. Differentially expressed genes (DEGs) relative to unstimulated controls were identified for each in vitro viral infection, as well as for both viral infections (shared DEGs). Pathway enrichment analysis was performed to associate identified DEGs with KEGG/biological pathways.

Results

We identified 2,906, 3,888, 681, and 446 DEGs in PBMCs, monocytes, B cells, and CD8+ T cells, respectively, in response to influenza stimulation. Meanwhile, 97, 120, 20, and 10 DEGs were identified as gene signatures in PBMCs, monocytes, B cells, and CD8+ T cells, respectively, upon vaccinia stimulation. The majority of DEGs identified in PBMCs were also found in monocytes after either viral stimulation. Of the virus-specific DEGs, 55, 63, and 9 DEGs occurred in common in PBMCs, monocytes, and B cells, respectively, while no DEGs were shared in infected CD8+ T cells after influenza and vaccinia. Gene set enrichment analysis demonstrated that these shared DEGs were over-represented in innate signaling pathways, including cytokine-cytokine receptor interaction, viral protein interaction with cytokine and cytokine receptor, Toll-like receptor signaling, RIG-I-like receptor signaling pathways, cytosolic DNA-sensing pathways, and natural killer cell mediated cytotoxicity.

Conclusion

Our results provide insights into virus-host interactions in different immune cells, as well as host defense mechanisms against viral stimulation. Our data also highlights the role of monocytes as a major cell population driving gene expression in ex vivo PBMCs in response to viral stimulation. The immune response signaling pathways identified in this study may provide specific targets for the development of novel virus-specific therapeutics and improved vaccines for vaccinia and influenza. Although influenza and vaccinia viruses have been selected in this study as pathogen models, this approach could be applicable to other pathogens.

An open-label, non-randomized study investigating the safety and efficacy of smallpox vaccine, LC16, as post-exposure prophylaxis for mpox

Mpox is an acute exanthematous disease caused by the monkeypox virus. Since May 2022, it has spread as a community-acquired infection, mainly in Europe and the United States, and urgent measures to prevent this infection were also required in Japan. In this study, we investigated the post-exposure prophylaxis of mpox and safety after inoculating the smallpox vaccine. Participants in close contact with patients with mpox were inoculated with "Freeze-dried cell culture Smallpox Vaccine LC16," within 14 days after close contact. Six cases were registered, and all the participants were inoculated. No mpox symptoms or related complications were observed in the participants for 21 days after the close contact. Adverse events due to inoculation, such as rash, fever, lymphadenopathy, and local reaction at the inoculation site (comprising erythema, swelling, induration, and pain) were observed in the participants; however, all inoculation-related events were non-severe and non-serious, and the participants recovered during the 28-day observation period. The findings of this study suggest that inoculation with LC16 is an effective post-exposure prophylaxis in individuals who had close contact with patients with mpox. Further large-scale studies are warranted to validate these findings.

Identification of novel T-cell epitopes on monkeypox virus and development of multi-epitopes vaccine using immunoinformatics approaches

Monkeypox virus (MPV) is closely related to the smallpox virus, and previous data from Africa suggest that the smallpox vaccine (VARV) is at least 85% effective in preventing MPV. No multi-epitope vaccine has yet been developed to prevent MPV infection. In this work, we used in silico structural biology and advanced immunoinformatic strategies to design a multi-epitope subunit vaccine against MPV infection. The designed vaccine sequence is adjuvanted with CpG-ODN and includes HTL/CTL epitopes for similar proteins between vaccinia virus (VACV) that induced T-cell production in vaccinated volunteers and the first draft sequence of the MPV genome associated with the suspected outbreak in several countries, May 2022. In addition, the specific binding of the modified vaccine and the immune Toll-like receptor 9 (TLR9) was estimated by molecular interaction studies. Strong interaction in the binding groove as well as good docking scores confirmed the stringency of the modified vaccine. The stability of the interaction was confirmed by a classical molecular dynamics simulation and normal mode analysis. Then, the immune simulation also indicated the ability of this vaccine to induce an effective immune response against MPV. Codon optimization and in silico cloning of the vaccine into the pET-28a (+) vector also showed its expression potential in the E. coli K12 system. The promising data obtained from the various in silico studies indicate that this vaccine is effective against MPV. However, additional in vitro and in vivo studies are still needed to confirm its efficacy.Communicated by Ramaswamy H. Sarma.

Post-exposure vaccine effectiveness and contact management in the mpox outbreak, Madrid, Spain, May to August 2022

BackgroundAppropriate vaccination strategies have been key to controlling the outbreak of mpox outside endemic areas in 2022, yet few studies have provided information on mpox vaccine effectiveness (VE).AimTo assess VE after one dose of a third-generation smallpox vaccine against mpox when given as post-exposure prophylaxis (PEP) within 14 days.MethodsA survival analysis in a prospective cohort of close contacts of laboratory-confirmed mpox cases was conducted from the beginning of the outbreak in the region of Madrid in May 2022. The study included contacts of cases in this region diagnosed between 17 May and 15 August 2022. Follow up was up to 49 days. A multivariate proportional hazard model was used to evaluate VE in the presence of confounding and interaction.ResultsInformation was obtained from 484 close contacts, of which 230 were vaccinated within 14 days of exposure. Of the close contacts, 57 became ill during follow-up, eight vaccinated and 49 unvaccinated. The adjusted effectiveness of the vaccine was 88.8% (95% CI: 76.0-94.7). Among sexual contacts, VE was 93.6% (95% CI: 72.1-98.5) for non-cohabitants and 88.6% (95% CI: 66.1-96.2) for cohabitants.ConclusionPost-exposure prophylaxis of close contacts of mpox cases is an effective measure that can contribute to reducing the number of cases and eventually the symptoms of breakthrough infections. The continued use of PEP together with pre-exposure prophylaxis by vaccination and other population-targeted prevention measures are key factors in controlling an mpox outbreak.

Serological responses to smallpox A33 antigen and monkeypox A35 antigen in healthy people and people living with HIV-1 from Guangzhou, China

People are expected to have been previously vaccinated with a Vaccinia-based vaccine, as until 1980 smallpox vaccination was a standard protocol in China. It is unclear whether people with smallpox vaccine still have antibody against vaccinia virus (VACV) and cross-antibody against monkeypox virus (MPXV). Herein, we assessed the binding antibodies with antigen of VACV-A33 and MPXV-A35 in the general population and HIV-1 infected patients. Firstly, we detected VACV antibody with A33 protein to evaluate the efficiency of smallpox vaccination. The result show that 29% (23 of 79) of hospital staff (age ≥ 42 years) and 63% (60 of 95) of HIV-positive patients (age ≥ 42 years) from Guangzhou Eighth People's Hospital were able to bind A33. However, among the subjects below 42 years of age, 1.5% (3/198) of the hospital volunteer samples and 1% (1/104) of the samples from HIV patients were positive for antibodies against A33 antigen. Then, we assessed the specific cross-reactive antibodies against MPXV A35 protein. 24% (19 of 79) hospital staff (age〉 = 42 years) and 44% (42 of 95) of HIV-positive patients (age〉 = 42 years) were positive. 98% (194/198) of the hospital staff and 99% (103/104) of the HIV patients had no A35-binding antibodies. Further, we found significant sex differences for the reactivity to A35 antigen were observed in HIV population, but no significant sex differences in hospital staff. Further, we analyzed the positivity rate of anti-A35 antibody of men who have sex with men (MSM) and non-MSM in HIV patients (age〉 = 42years). We found that 47% of no-MSM population and 40% of MSM population were positive for A35 antigen, with no significant difference. Lastly, we found only 59 samples were positive for anti-A33 IgG and anti-A35 IgG in all participants. Together, we demonstrated A33 and A35 antigens binding antibodies were detected in HIV patients and general population who were older than 42 years, and cohort studies only provided data of serological detection to support early response to monkeypox outbreak.

Human monkeypox - After 40 years, an unintended consequence of smallpox eradication

Monkeypox is one of the many zoonotic viruses that belong to the Orthopoxvirus genus of the Poxviridae family with a similar clinical appearance to smallpox. The symptoms of monkeypox include fever, headache, muscle aches, and lymphadenopathy. The transmission of monkeypox occurs from infected animals to humans or through direct contact (sexual or skin-to-skin), respiratory droplets, and clothing such as towels. The incidence of monkeypox is rising drastically over the world. This short communication discusses the causes of the rising monkeypox cases and emphasizes strategies to prevent the spread of the virus.

Monkeypox Cross-Sectional Survey of Knowledge, Attitudes, Practices, and Willingness to Vaccinate among University Students in Pakistan

This study aimed to explore knowledge, attitude, perceptions, and willingness regarding vaccination among university students in Pakistan. This cross-sectional study was carried out using an open online self-administered survey via Google Forms. The survey data were collected between the 15 to 30 of October 2022. A total of 946 respondents participated in the study, of which the majority were female (514, 54.3%). Most students belonged to a medical background, specifically pharmaceutical sciences. Most of the respondents did not know about monkeypox before 2022 (646, 68.3%). Regarding overall knowledge of monkeypox, most of the respondents had average knowledge (726, 76.7%), with very few having good knowledge (60, 6.3%). Regarding overall attitudes towards monkeypox, most of the respondents had neutral attitudes (648, 68.5%). There was a significant association between knowledge of Monkeypox with the type of academic degree (p < 0.001), type of discipline (p < 0.001), and region of respondents (p < 0.001). The willingness to vaccinate among the population was (67.7%). The current study pointed out that the overall knowledge of monkeypox was average in most respondents, with considerable knowledge gaps in most aspects. The overall attitude towards monkeypox was neutral. Further, the knowledge about monkeypox was strongly associated with academic degree, study discipline, and region of respondents. Our findings emphasize the need to raise public awareness by educating students on the monkeypox virus. This will improve adherence to preventative recommendations.

Genomic Characterization of the Historical Smallpox Vaccine Strain Wyeth Isolated from a 1971 Seed Vial

The Wyeth strain of vaccinia virus (VACV) produced by Wyeth Pharmaceuticals was supposedly used to manufacture the old freeze-dried American smallpox vaccine, Dryvax, until its discontinuation in 2008. Although the genomic sequences of numerous Dryvax clones have been reported, data on VACV-Wyeth genomes are still lacking. Genomic analysis of old VACV strains is relevant to understand the evolutionary relationships of smallpox vaccines, particularly with the recent resumption of smallpox vaccination in certain population groups as an attempt to control the worldwide monkeypox outbreak. Here we analyzed the complete genome sequences of three VACV-Wyeth clonal isolates obtained from a single seed vial donated to the Brazilian eradication program in the 1970s. Wyeth clones show >99.3% similarity to each other and >95.3% similarity with Dryvax clones, mapping together in clade I of the vaccinia group. Although the patterns of SNPs and INDELs comparing Dryvax and Wyeth clones are overall uniform, important differences were detected particularly at the ends of the genome. In addition, we detected recombinant events of clone Wyeth A111 and the Dryvax clone Acam2000, suggesting that other regions of the genomes may have similar patchy patterns of recombination. A small-scale serological survey using VACV-Wyeth as antigen in ELISA assays revealed that 63 of the 65 individuals born before the end of smallpox vaccination in Brazil still have anti-VACV IgG antibodies, demonstrating the usefulness of the VACV-Wyeth strain in future extended serological studies of the Brazilian population.

Monkeypox Knowledge and Vaccine Hesitancy of Czech Healthcare Workers: A Health Belief Model (HBM)-Based Study

BACKGROUND

The recent human monkeypox virus (HMPXV) outbreak in non-endemic countries that started in May 2022 has raised concerns among public health authorities worldwide. Healthcare workers (HCWs) play a decisive role during epidemics in transmitting accurate information to the public and motivating them to pursue protective behaviours, including immunisation.

METHODS

A cross-sectional survey-based study was conducted in the Czech Republic in September 2022 to evaluate HMPXV-related knowledge and vaccination perceptions among HCWs. The study utilised a digital self-administered questionnaire (SAQ) to collect data from the target population. The proposed SAQ inquired about participants' sociodemographic and anamnestic characteristics, perceived knowledge of HMPXV, factual knowledge, and vaccination perceptions according to the health belief model (HBM).

RESULTS

A total of 341 participants were included in this study; most of them were females (88.9%), allied HCWs (89.4%), heterosexuals (87.1%), married (61.9%), and vaccinated against COVID-19 (91.2%). Only 8.8% of the participants agreed to receive vaccination against HMPXV; 44.9% rejected it, while 46.3% were hesitant. While digital news portals (47.5%) and social media (25.8%) were among the most utilised sources of information about HMPXV, the scientific journals (5.6%), ECDC (5%), and the U.S. CDC (1.5%) were the least common sources. The participants demonstrated suboptimal levels of factual knowledge, especially regarding HMPXV vaccines (1.5 ± 1.2 (0-4)) and treatments (0.9 ± 0.9 (0-4)). Additionally, several misconceptions were detectable among the participants, regarding topics such as the availability of effective vaccines and antivirals against HMPXV, the risk of vertical transmission, and homosexual stigmatisation. The HBM indicated that the cues to action and perceived susceptibility were the most important constructs to predict HMPXV vaccine acceptance.

CONCLUSIONS

the findings of this study call upon public health practitioners and health policymakers in the Czech Republic to act accordingly in order to determine the drivers of vaccine hesitancy among Czech HCWs. Dedicated educational campaigns should aim to counter the HCWs' misconceptions around HMPXV, and future studies should aim to explore the prevalence and drivers of HMPXV vaccine hesitancy among the general population.

Increased outbreaks of monkeypox highlight gaps in actual disease burden in Sub-Saharan Africa and in animal reservoirs

We explain research gaps on Monkeypox (MPX) virus epidemiology in endemic countries and present hypotheses for the recent increase of MPX cases in West Africa as a possible explanation for the current epidemic in Europe, America, and Australia. The detection of >400 MPX cases in less than a month in May 2022, across many countries underscores the epidemic potential of MPX in humans and demonstrates several important research gaps. First, the true burden of MPX in West and Central Africa is poorly understood, although it is critical for prevention and control of future outbreaks. Second, the diversity and extent of the animal reservoir remain unknown. We hypothesize that the synanthropic rodent population has increased in recent years in Africa leading to more human-rodent interactions and thus increased transmission of MPXV. We further hypothesise that nearly 45 years after the end of routine smallpox vaccination, the larger and more interconnected immune-naïve population has crossed a threshold resulting in more sustainable human-to-human transmission of MPXV. The current epidemic in the Western World is possibly a consequence of increased local transmission of MPXV in Africa. A new estimation of the basic and effective reproduction rate (R0 and Re) in different populations is required. National, regional, and international collaborations are needed to address research gaps related to MPX outbreaks.

Interferon α/β Decoy Receptor Encoded by a Variant in the Dryvax Smallpox Vaccine Contributes to Virulence and Correlates with Severe Vaccine Side Effects

Although providing long-lasting immunity, smallpox vaccination was associated with local and systemic reactions and rarely with severe complications, including progressive vaccinia and postvaccinia encephalitis. As the Dryvax smallpox vaccine consists of a population of variants, we investigated a particularly pathogenic isolate called clone 3 (CL3). Virus replication was monitored by inserting the gene encoding firefly luciferase (Luc) into the genomes of CL3 and ACAM2000, the second-generation smallpox vaccine derived from a less virulent clone. Greater luminescence occurred following intranasal or intraperitoneal inoculation of mice with CL3-Luc than ACAM2000-Luc. Previous genome sequencing of CL3 and ACAM2000 revealed numerous differences that could affect pathogenicity. We focused on a 4.2-kbp segment, containing several open reading frames, in CL3 that is absent from ACAM2000 and determined that lower virulence of the latter was associated with a truncation of the interferon α/β (IFN-α/β) decoy receptor. Truncation of the decoy receptor in CL3-Luc and repair of the truncated version in ACAM2000-Luc decreased and increased virulence, respectively. Blockade of the mouse type 1 IFN receptor increased the virulence of ACAM2000-Luc to that of CL3-Luc, consistent with the role of IFN in attenuating the former. The severities of disease following intracranial inoculation of immunocompetent mice and intraperitoneal inoculation of T cell-depleted mice were also greater in viruses expressing the full-length decoy receptor. Previous evidence for the low affinity of a similarly truncated decoy receptor for IFN and the presence of a full-length decoy receptor in virus isolated from a patient with progressive vaccinia support our findings.

Comment on the article “With regard to the bicentennial of the independence of Colombia: Reading practices of Antonio Nariño and the development of a presumably effective vaccine against smallpox

For the American colonies, smallpox implied a process that dramatically destabilized their sociodemographic dynamics, which explains why scientific development took place around the causative virus. Each book about smallpox in Nariño’s library was a tool in the fight against smallpox undertaken by the founding father. After reviewing the article “About the bicentennial of the independence of Colombia: The reading practices of Antonio Nariño and the development of a vaccine that is presumably effective against smallpox” (1), I set myself to study Antonio Nariño’s medical knowledge further. Through the approach to the works that Nariño used to educate himself on smallpox and the development of a biographical sketch of each of them, I analyzed the process of variolization in the Kingdom of Nueva Granada and the need to manufacture a vaccine locally.

Myopericarditis Associated With Smallpox Vaccination Among US Army Personnel - Fort Hood, Texas, 2018

OBJECTIVE

In March 2018, the US Department of Defense (DOD) added the smallpox vaccination, using ACAM2000, to its routine immunizations, increasing the number of persons receiving the vaccine. The following month, Fort Hood reported a cluster of 5 myopericarditis cases. The Centers for Disease Control and Prevention and the DOD launched an investigation.

METHODS

The investigation consisted of a review of medical records, establishment of case definitions, causality assessment, patient interviews, and active surveillance. A 2-sided exact rate ratio test was used to compare myopericarditis incidence rates.

RESULTS

This investigation identified 4 cases of probable myopericarditis and 1 case of suspected myopericarditis. No alternative etiology was identified as a cause. No additional cases were identified. There was no statistically significant difference in incidence rates between the observed cluster (5.23 per 1000 vaccinated individuals, 95% CI: 1.7-12.2) and the ACAM2000 clinical trial outcomes for symptomatic persons, which was 2.29 per 1000 vaccinated individuals (95% CI: 0.3-8.3).

CONCLUSIONS

Vaccination with ACAM2000 is the presumptive cause of this cluster. Caution should be exercised before considering vaccination campaigns for smallpox given the clinical morbidity and costs incurred by a case of myopericarditis. Risk of myopericarditis should be carefully weighed with risk of exposure to smallpox.

Polymorphisms in STING Affect Human Innate Immune Responses to Poxviruses

We conducted a large genome-wide association study (GWAS) of the immune responses to primary smallpox vaccination in a combined cohort of 1,653 subjects. We did not observe any polymorphisms associated with standard vaccine response outcomes (e.g., neutralizing antibody, T cell ELISPOT response, or T cell cytokine production); however, we did identify a cluster of SNPs on chromosome 5 (5q31.2) that were significantly associated (p-value: 1.3 x 10⁻¹² – 1.5x10⁻³⁶) with IFNα response to in vitro poxvirus stimulation. Examination of these SNPs led to the functional testing of rs1131769, a non-synonymous SNP in TMEM173 causing an Arg-to-His change at position 232 in the STING protein—a major regulator of innate immune responses to viral infections. Our findings demonstrate differences in the ability of the two STING variants to phosphorylate the downstream intermediates TBK1 and IRF3 in response to multiple STING ligands. Further downstream in the STING pathway, we observed significantly reduced expression of type I IFNs (including IFNα) and IFN-response genes in cells carrying the H232 variant. Subsequent molecular modeling of both alleles predicted altered ligand binding characteristics between the two variants, providing a potential mechanism underlying differences in inter-individual responses to poxvirus infection. Our data indicate that possession of the H232 variant may impair STING-mediated innate immunity to poxviruses. These results clarify prior studies evaluating functional effects of genetic variants in TMEM173 and provide novel data regarding genetic control of poxvirus immunity.

Preemptive Tecovirimat Use in an Active Duty Service Member Who Presented With Acute Myeloid Leukemia After Smallpox Vaccination

Smallpox vaccine is contraindicated in immunosuppression due to increased risk for adverse reactions (eg, progressive vaccinia). We describe the first-ever use of tecovirimat as a preemptive vaccinia virus treatment strategy during induction chemotherapy in an active duty service member who presented with acute leukemia and inadvertent autoinoculation after smallpox vaccination.

With regard to the bicentennial of the independence of Colombia: Reading practices of Antonio Nariño and the development of a presumably effective vaccine against smallpox

Introduction: The social history of written culture reflects the reading and writing habits and practices that allow us to appropriate the texts to build our sense of community. Hence, the library of individuals reflects their reading habits, their way of imagining nature, their relationship with political and religious power, and their involvement with society. Objective: To interpret Antonio Nariño’s reading practices by means of the medical books in his library to approach the way he developed a presumably effective vaccine against smallpox. Materials and methods: We made a bibliographic description of the documents “Confiscación y embargo de bienes de Nariño” and “Papeles, libros y bienes de Sebastián López Ruiz en poder de Nariño” from the Nariño Archive of the Universidad Nacional de Colombia. Results: Out of the 39 books about Medicine (seven treatises on surgery, 12 compendia of practical exercise, 11 disease manuals, seven compendia of medical topics, and two books on childbirth) three were smallpox treatises. Conclusion: Antonio Nariño’s medical and scientific practice reflects his reading and writing habits, his skills and competences, and his cultural attitudes, which promoted the notion of public health. The study of Nariño as a self-taught physician allowed for relating the scientific production techniques (development of the vaccine) and the cultural materiality (state of the art) based on the medical texts in his library.

Developing the concept of beneficial non-specific effect of live vaccines with epidemiological studies

BACKGROUND

Epidemiological and immunological studies are increasingly reporting non-specific effects (NSEs) of vaccines; i.e. vaccines may affect the risk and severity of non-targeted infections. We reviewed how epidemiological studies developed the concept of beneficial NSEs of live vaccines.

SOURCES

This is a personal narrative of how we came to pursue the concept of NSEs in studies of measles vaccine (MV) from the late 1970s. We also searched Pubmed for epidemiological studies of nonspecific/non-specific effects (NSEs) of the most common human vaccines.

CONTENT

When smallpox vaccine was introduced around 1800, bacillus Calmette-Guérin (BCG) against tuberculosis in the 1920s and oral polio vaccine (OPV) in the 1960s, there were suggestions that these live attenuated vaccines reduced mortality more than expected. However, scientific follow-up was limited and the concept of beneficial NSEs did not become mainstream. We observed beneficial NSEs after MV was introduced in low-income countries in the 1970s. Subsequent observational studies and randomized trials confirmed beneficial NSEs of smallpox vaccine, BCG and OPV. Recently, beneficial NSEs have been claimed for the non-live diphtheria-tetanus-pertussis and rabies vaccines. However, no non-live vaccine has yet been documented to produce beneficial NSEs.

IMPLICATIONS

Observational and experimental research has shown beneficial NSEs of four live attenuated vaccines: smallpox vaccine, BCG, OPV and MV. With immunological evidence now supporting the epidemiological observations, it is urgent to take both the specific and NSEs into account in the planning of vaccination programmes.

Vaccinations against smallpox and tuberculosis are associated with better long-term survival: a Danish case-cohort study 1971-2010

Background: When vaccinations with vaccinia against smallpox and Bacillus Calmette-Guérin (BCG) against tuberculosis were phased out in some high-income countries around 1980, the impact on overall mortality was not examined. Recent studies from low-income countries have suggested that these vaccines are associated with mortality reductions, not explained by specific disease protection. We examined whether vaccinia and BCG administered in childhood were associated with long-term mortality reductions in a high-income population.

Methods: In this case-cohort study, we followed 47 622 schoolchildren from Copenhagen, Denmark, born 1965 to 1976, from their first health examination to 2010. This cohort experienced the phase-out of vaccinia and BCG vaccination programmes.

Results: A sub-cohort of 5 316 individuals (699 excluded) was followed for 164 450 person-years (0.2% were lost to follow-up), and 401 deaths due to natural causes (841 deaths in total) occurred in the full cohort. Compared with individuals who had not received vaccinia or BCG, those who had received both vaccinia and BCG had an adjusted hazard ratio (aHR) of 0.54 [95% confidence interval (CI): 0.36–0.81] for mortality due to natural causes of death; those who only received BCG had an aHR of 0.58 (95% CI: 0.39–0.85). Vaccinia and BCG were not associated with any protection against deaths by accidents, suicide or murder, the combined aHR being 0.94 (95% CI: 0.62–1.42).

Conclusions: Vaccinia and BCG vaccinations were associated with better long-term survival, which was not explained by specific protection. Vaccines with beneficial non-specific effects may reduce overall mortality even after the target diseases are eradicated.

Vaccinia Virus Natural Infections in Brazil: The Good, the Bad, and the Ugly

The orthopoxviruses (OPV) comprise several emerging viruses with great importance to human and veterinary medicine, including vaccinia virus (VACV), which causes outbreaks of bovine vaccinia (BV) in South America. Historically, VACV is the most comprehensively studied virus, however, its origin and natural hosts remain unknown. VACV was the primary component of the smallpox vaccine, largely used during the smallpox eradication campaign. After smallpox was declared eradicated, the vaccination that conferred immunity to OPV was discontinued, favoring a new contingent of susceptible individuals to OPV. VACV infections occur naturally after direct contact with infected dairy cattle, in recently vaccinated individuals, or through alternative routes of exposure. In Brazil, VACV outbreaks are frequently reported in rural areas, affecting mainly farm animals and humans. Recent studies have shown the role of wildlife in the VACV transmission chain, exploring the role of wild rodents as reservoirs that facilitate VACV spread throughout rural areas. Furthermore, VACV circulation in urban environments and the significance of this with respect to public health, have also been explored. In this review, we discuss the history, epidemiological, ecological and clinical aspects of natural VACV infections in Brazil, also highlighting alternative routes of VACV transmission, the factors involved in susceptibility to infection, and the natural history of the disease in humans and animals, and the potential for dissemination to urban environments.

A Single Vaccination of Nonhuman Primates with Highly Attenuated Smallpox Vaccine, LC16m8, Provides Long-term Protection against Monkeypox

Monkeypox virus (MPXV) causes human monkeypox (human MPX), which is a similar disease to smallpox in humans. A previous study showed that a single vaccination of monkeys with LC16m8, a highly attenuated smallpox vaccine, protected them from MPX from 4-5 weeks post-vaccination. In this study, we evaluated the long-term efficacy of a single vaccination with LC16m8 in a nonhuman primate model of MPXV infection. The monkeys were inoculated with either LC16m8, Lister (parental strain of LC16m8), or a mock-up vaccine, and then challenged with MPXV via a subcutaneous route, at 6 and 12 months after vaccination, which we compared with either Lister or the mock-up vaccination. The LC16m8 monkeys exhibited almost no MPX-associated symptoms, whereas most of the naïve monkeys died. LC16m8 generated the protective memory immune response against MPXV, as suggested by the immediate viremia reduction and the response of the IgG antibody. The results demonstrated that the vaccination of monkeys with a single dose of LC16m8 provided durable protection against MPXV for longer than one year after immunization. The results suggest that the vaccination of humans with LC16m8 could induce long-term protection against MPXV infection.

The Effect of Smallpox and Bacillus Calmette-Guérin Vaccination on the Risk of Human Immunodeficiency Virus-1 Infection in Guinea-Bissau and Denmark

Background

The live smallpox and Bacillus Calmette-Guérin (BCG) vaccinations have been associated with better adult survival in both Guinea-Bissau and Denmark. In Guinea-Bissau, human immunodeficiency virus (HIV)-1 became an important cause of death after smallpox vaccination was phased out globally in 1980. We hypothesised that smallpox and BCG vaccinations were associated with a lower prevalence of HIV-1 infection, and we tested this hypothesis in both Guinea-Bissau and Denmark.

Methods

We conducted 2 studies: (1) a cross-sectional study of HIV infection and vaccination scars in Guinea-Bissau including 1751 individuals and (2) a case-base study with a background population of 46239 individuals in Denmark. In Guinea-Bissau, HIV-1 transmission was almost exclusively sexually transmitted. In Denmark, we excluded intravenous drug users. Data were analyzed using logistic regression.

Results

Bacillus Calmette-Guérin and/or smallpox vaccination compared with neither of these vaccines was associated with an adjusted odds ratio (aOR) for HIV-1 of 0.62 (95% confidence interval [CI], 0.36–1.07) in Guinea-Bissau and 0.70 (95% CI, 0.43–1.15) in Denmark. We combined the results from both settings in a meta-analysis (aOR = 0.66; 95% CI, 0.46–0.96). Data from Guinea-Bissau indicated a stronger effect of multiple smallpox vaccination scars (aOR = 0.27; 95% CI, 0.10–0.75) as follows: women, aOR = 0.18 (95% CI, 0.05–0.64); men, aOR = 0.52 (95% CI, 0.12–2.33); sex-differential effect, P = .29.

Conclusions

The studies from Guinea-Bissau and Denmark, 2 very different settings, both suggest that the BCG and smallpox vaccines could be associated with a decreased risk of sexually transmitted HIV-1. It might be informative to pursue this observation and explore possible protective mechanisms as part of the search for an HIV-1 vaccine.

Cross-Neutralizing and Protective Human Antibody Specificities to Poxvirus Infections

Monkeypox (MPXV) and cowpox (CPXV) are emerging agents that cause severe human infections on an intermittent basis, and variola virus (VARV) has potential for use as an agent of bioterror. Vaccinia immune globulin (VIG) has been used therapeutically to treat severe orthopoxvirus infections but is in short supply. We generated a large panel of orthopoxvirus-specific human monoclonal antibodies (Abs) from immune subjects to investigate the molecular basis of broadly neutralizing antibody responses for diverse orthopoxviruses. Detailed analysis revealed the principal neutralizing antibody specificities that are cross-reactive for VACV, CPXV, MPXV, and VARV and that are determinants of protection in murine challenge models. Optimal protection following respiratory or systemic infection required a mixture of Abs that targeted several membrane proteins, including proteins on enveloped and mature virion forms of virus. This work reveals orthopoxvirus targets for human Abs that mediate cross-protective immunity and identifies new candidate Ab therapeutic mixtures to replace VIG.

Population at Risk of Severe Adverse Events from Replicating Smallpox Vaccine

OBJECTIVE

To quantify the population at risk of serious adverse reactions to replicating smallpox vaccine.

DESIGN AND SAMPLE

Conditions known or suspected to carry risk were identified via Centers for Disease Control and Prevention planning documents, other federal publications, and peer-reviewed literature. Conditions identified were categorized as historically recognized risks or more recently recognized immunocompromised states that may pose risk. Major historical risk factors were as follows: eczema/atopic dermatitis, pregnancy, HIV, and primary immunodeficiency. More recently identified states were as follows: rheumatoid arthritis, inflammatory bowel disease, dialysis, bone marrow transplant recipients within 24 months post-transplant, solid-organ transplant recipients within 3 months post-transplant, age under 1 year, and systemic lupus erythematosus.

MEASURES

The estimated prevalence or absolute number of affected individuals for each condition was ascertained from peer-reviewed studies, vital statistics, and registry databases.

RESULTS

An estimated 48,121,280 to 50,028,045 individuals (15.2-15.8% of the U.S. population) are potentially contraindicated to replicating smallpox vaccine. This rises to 119,244,531 to 123,669,327 (37.4-38.8%) if household contacts are included.

CONCLUSIONS

These figures are significant and larger than the only previously published study. Understanding this number allows for improved clinical utilization, equitable attention to the health needs of a vulnerable population, and strategic vaccine stockpiling.

Defending against smallpox: a focus on vaccines

Smallpox has shaped human history, from the earliest human civilizations well into the 20th century. With high mortality rates, rapid transmission, and serious long-term effects on survivors, smallpox was a much-feared disease. The eradication of smallpox represents an unprecedented medical victory for the lasting benefit of human health and prosperity. Concerns remain, however, about the development and use of the smallpox virus as a biological weapon, which necessitates the need for continued vaccine development. Smallpox vaccine development is thus a much-reviewed topic of high interest. This review focuses on the current state of smallpox vaccines and their context in biodefense efforts.

Cytokine production associated with smallpox vaccine responses

Smallpox was eradicated 34 years ago due to the success of the smallpox vaccine; yet, the vaccine continues to be studied because of its importance in responding to potential biological warfare and the adverse events associated with current smallpox vaccines. Interindividual variations in vaccine response are observed and are, in part, due to genetic variation. In some cases, these varying responses lead to adverse events, which occur at a relatively high rate for the smallpox vaccine compared with other vaccines. Here, we aim to summarize the cytokine responses associated with smallpox vaccine response to date. Along with a description of each of these cytokines, we describe the genetic and adverse event data associated with cytokine responses to smallpox vaccination.

Smallpox Vaccination of Laboratory Workers at US Variola Testing Sites

To evaluate the need to revaccinate laboratory workers against smallpox, we assessed regular revaccination at the US Laboratory Response Network’s variola testing sites by examining barriers to revaccination and the potential for persistence of immunity. Our data do not provide evidence to suggest prolonging the recommended interval for revaccination.

Mathematical modeling provides kinetic details of the human immune response to vaccination

With major advances in experimental techniques to track antigen-specific immune responses many basic questions on the kinetics of virus-specific immunity in humans remain unanswered. To gain insights into kinetics of T and B cell responses in human volunteers we combined mathematical models and experimental data from recent studies employing vaccines against yellow fever and smallpox. Yellow fever virus-specific CD8 T cell population expanded slowly with the average doubling time of 2 days peaking 2.5 weeks post immunization. Interestingly, we found that the peak of the yellow fever-specific CD8 T cell response was determined by the rate of T cell proliferation and not by the precursor frequency of antigen-specific cells as has been suggested in several studies in mice. We also found that while the frequency of virus-specific T cells increased slowly, the slow increase could still accurately explain clearance of yellow fever virus in the blood. Our additional mathematical model described well the kinetics of virus-specific antibody-secreting cell and antibody response to vaccinia virus in vaccinated individuals suggesting that most of antibodies in 3 months post immunization were derived from the population of circulating antibody-secreting cells. Taken together, our analysis provided novel insights into mechanisms by which live vaccines induce immunity to viral infections and highlighted challenges of applying methods of mathematical modeling to the current, state-of-the-art yet limited immunological data.

HLA alleles associated with the adaptive immune response to smallpox vaccine: a replication study

We previously reported HLA allelic associations with vaccinia virus (VACV)-induced adaptive immune responses in a cohort of healthy individuals (n = 1,071 subjects) after a single dose of the licensed smallpox (Dryvax) vaccine. This study demonstrated that specific HLA alleles were significantly associated with VACV-induced neutralizing antibody (NA) titers (HLA-B*13:02, *38:02, *44:03, *48:01, and HLA-DQB1*03:02, *06:04) and cytokine (HLA-DRB1*01:03, *03:01, *10:01, *13:01, *15:01) immune responses. We undertook an independent study of 1,053 healthy individuals and examined associations between HLA alleles and measures of adaptive immunity after a single dose of Dryvax-derived ACAM2000 vaccine to evaluate previously discovered HLA allelic associations from the Dryvax study and determine if these associations are replicated with ACAM2000. Females had significantly higher NA titers than male subjects in both study cohorts [median ID50 discovery cohort 159 (93, 256) vs. 125 (75, 186), p < 0.001; replication cohort 144 (82, 204) vs. 110 (61, 189), p = 0.024]. The association between the DQB1*03:02 allele (median ID50 discovery cohort 152, p = 0.015; replication cohort 134, p = 0.010) and higher NA titers was replicated. Two HLA associations of comparable magnitudes were consistently found between DRB1*04:03 and DRB1*08:01 alleles and IFN-γ ELISPOT responses. The association between the DRB1*15:01 allele with IFN-γ secretion was also replicated (median pg/mL discovery cohort 182, p = 0.052; replication cohort 203, p = 0.014). Our results suggest that smallpox vaccine-induced adaptive immune responses are significantly influenced by HLA gene polymorphisms. These data provide information for functional studies and design of novel candidate smallpox vaccines.

Genetic variation in IL18R1 and IL18 genes and Inteferon γ ELISPOT response to smallpox vaccination: an unexpected relationship

BACKGROUND

Genetic association studies demonstrated a role for cytokine proteins and cytokine or cytokine receptor gene polymorphisms in smallpox vaccine-induced adaptive immunity.

METHODS

We examined the association of genetic polymorphisms with cellular (interferon [IFN] γ enzyme-linked immunospot assay [ELISPOT]) immune response to smallpox vaccine in 1076 immunized individuals.

RESULTS

The majority of significant associations were discovered between single-nucleotide polymorphisms/haplotypes in IL18R1 and IL18 genes, in which we previously reported an association with vaccinia virus-induced neutralizing antibody titers in this study cohort. A functional coding IL18R1 polymorphism (rs1035130/Phe251Phe; P = .01) was significantly associated with an allele dose-related increase in IFN-γ production and was also associated with vaccinia-specific neutralizing antibody titers. Significant associations were also found between IL18R1 haplotypes and variations in IFN-γ ELISPOT responses (global P < .0001).

CONCLUSIONS

Our data suggest the importance of variants in the IL18R1 and IL18 genetic loci for broad-based smallpox vaccine-induced adaptive immunity.

Antonio Gimbernat y Arbós: an anatomist-surgeon of the Enlightenment (in the 220th anniversary of his "A new method of operating the crural hernia")

This article focuses on Antonio de Gimbernat y Arbós (1734-1816), with particular attention paid to his famous publication "Nuevo método de operar en la hernia crural" (2013 marking its 220 anniversary), which was translated into English by Thomas Beddoe two years later (A new method of operating for the femoral hernia Translated from the Spanish of Don Antonio de Gimbernat, To which are added, with plates by the translator, queries respecting a safer method of performing inoculation). Antonio de Gimbernat y Arbós, a Spanish anatomist and surgeon, was one of the pioneers during the "Age of Dissection" (late 18th Century). He was a man of great willpower, bright, thorough, and unique. From his careful anatomical study in the inguinal region, he made a detailed description of the lacunar ligament, which John Hunter called the Gimbernat's ligament in his honor. Antonio de Gimbernat y Arbós also proposed an advanced treatment for strangulated femoral hernias. He acquired extraordinarily broad surgical skills with therapeutic orientation, conservative, not aggressive, based on the knowledge he had gained through dissection. Furthermore, though this is less well known nowadays, Antonio de Gimbernat y Arbós was also relevant organizer of education and health-services - as it was the custom of the great physician of this time. Consequently, Antonio de Gimbernat y Arbós is truly representative of the great figures of the anatomists-surgeons of the Enlightenment.

Smallpox vaccine with integrated IL-15 demonstrates enhanced in vivo viral clearance in immunodeficient mice and confers long term protection against a lethal monkeypox challenge in cynomolgus monkeys

Despite the eradication of smallpox, there is heightened concern that it could be reintroduced as a result of intentional release of Variola major virus through an act of bioterrorism. The live vaccine that was pivotal in the eradication of smallpox though considered a gold standard for its efficacy still retains sufficient residual virulence that can cause life-threatening sequelae especially in immune deficient individuals. Therefore, a safer smallpox vaccine that can match the efficacy of first generation vaccines is urgently needed. We previously reported that the integration of human IL-15 cytokine into the genome of Wyeth strain of vaccinia (Wyeth/IL-15), the same strain as the licensed vaccine, generates a vaccine with superior immunogenicity and efficacy in a mouse model. We now demonstrate that Wyeth/IL-15 is non-lethal to athymic nude mice when administered intravenously at a dose of 10(7) plaque forming units and it undergoes enhanced in vivo clearance in these immune deficient mice. Furthermore, a majority of cynomolgus monkeys vaccinated with vaccinia viruses with integrated IL-15, when challenged 3 years later with a lethal dose of monkeypox virus displayed milder clinical manifestations with complete recovery supporting the utility of Wyeth/IL-15 for contemporary populations as a safer and efficacious smallpox vaccine.

Smallpox vaccines for biodefense

Few diseases can match the enormous impact that smallpox has had on mankind. Its influence can be seen in the earliest recorded histories of ancient civilizations in Egypt and Mesopotamia. With fatality rates up to 30%, smallpox left its survivors with extensive scarring and other serious sequelae. It is estimated that smallpox killed 500 million people in the 19th and 20th centuries. Given the ongoing concerns regarding the use of variola as a biological weapon, this review will focus on the licensed vaccines as well as current research into next-generation vaccines to protect against smallpox and other poxviruses.

Evaluation of the efficacy of modified vaccinia Ankara (MVA)/IMVAMUNE against aerosolized rabbitpox virus in a rabbit model

Infection of rabbits with aerosolized rabbitpox virus (RPXV) produces a disease similar to monkeypox and smallpox in humans and provides a valuable, informative model system to test medical countermeasures against orthopoxviruses. Due to the eradication of smallpox, the evaluation of the efficacy of new-generation smallpox vaccines depends on relevant well-developed animal studies for vaccine licensure. In this study, we tested the efficacy of IMVAMUNE [modified vaccinia Ankara-Bavarian Nordic (MVA-BN)] for protecting rabbits against aerosolized RPXV. Rabbits were vaccinated with either phosphate-buffered saline (PBS), Dryvax, a single low dose of IMVAMUNE, a single high dose of IMVAMUNE, or twice with a high dose of IMVAMUNE. Aerosol challenge with a lethal dose of RPXV was performed 4 weeks after the last vaccination. All PBS control animals succumbed to the disease or were euthanized because of the disease within 7 days postexposure. The rabbits vaccinated with Dryvax, a low dose of IMVAMUNE, or a single high dose of IMVAMUNE showed minimal to moderate clinical signs of the disease, but all survived the challenge. The only clinical sign displayed by rabbits that had been vaccinated twice with a high dose of IMVAMUNE was mild transient anorexia in just two out of eight rabbits. This study shows that IMVAMUNE can be a very effective vaccine against aerosolized RPXV.

Gender effects on humoral immune responses to smallpox vaccine

There are no data currently available on gender and racial variation in smallpox vaccine immune responses. We recruited 1076 healthy adults 18-40 years old who received one dose of the US-licensed smallpox vaccine (Dryvax). Vaccinia neutralizing antibody titers in each subject's serum were determined using a high throughput neutralization assay based on a recombinant, beta-gal expressing vaccinia virus. Results are reported as the serum dilution inhibiting 50% of virus activity (ID(50)). The median ID(50) for all subjects was 132.2 (inter-quartile range (IQR)=78.8, 205.6). While no significant differences were observed with race and ethnicity, females had significantly higher neutralizing antibody titers than males (158.5 [93.2, 255.8] vs. 124.1 [75.2, 185.9]; p<0.0001). As expected, time since vaccination was also associated with variations in neutralizing antibody titers in our subjects. These data indicate that neutralizing antibody titers following primary smallpox vaccination vary by gender.

Electrocardiography screening for cardiotoxicity after modified Vaccinia Ankara vaccination

BACKGROUND

Symptomatic myopericarditis has been described after smallpox vaccination using replication-competent vaccinia strains.

METHODS

We examined the incidence of new electrocardiogram (ECG) abnormalities and evaluated the safety and immunogenicity related to vaccination. Volunteer subjects (n=90) aged 18 to 32 years were enrolled in a National Institutes of Health-sponsored phase I smallpox vaccination trial (Division of Microbiology and Infectious Diseases 02-017) and observed over a 26-week period after 2 injections of IMVAMUNE, Modified Vaccinia Ankara vaccine (Bavarian Nordic A/S, Copenhagen, DK), followed by scarification with Dryvax (Wyeth Laboratories, Marietta, Penn). Diagnostic computer-derived ECG statements were available to the clinical study team and compared with those of a board-certified cardiologist who independently read the ECG tracings.

RESULTS

Serial ECG tracings available for 89 of the subjects revealed new ST-segment abnormalities in 2.2% and new T-wave abnormalities in 15.7%; the majority (71.4%) resolved on subsequent tracings. Cardiologist over-read of computer statements resulted in frequent changes in readings, particularly negation of cardiac arrhythmias. A cardiology consultation was requested in 17 subjects for nonspecific cardiac symptoms or new abnormal ECG findings. Echocardiograms were performed in 12 of the 17 subjects and were normal except for 1 subject with possible myopericarditis after receiving Dryvax.

CONCLUSION

New minor ECG abnormalities are common in apparently young healthy volunteers considered for smallpox vaccination trials. Cardiologist over-read of computer-generated ECG statements in vaccine trials using ECG as a screening tool for safety can reduce false-positive computer-determined ECG diagnoses and the need for inappropriate cardiology referral and additional noninvasive testing.

Clonal vaccinia virus grown in cell culture fully protects monkeys from lethal monkeypox challenge

The potential use of smallpox as an agent of bioterrorism has renewed interest in the development of a modern vaccine capable of replacing the standard Dryvax vaccine. Vaccinia virus (ACAM2000), clonally isolated from Dryvax and manufactured in cell culture, was tested for immunogenicity and protective activity in a non-human primate model. Cynomolgus monkeys vaccinated with ACAM2000, Dryvax, or ACAM2000 diluent (control) were challenged 2 months post-vaccination with a lethal, intravenous dose of monkeypox virus. ACAM2000 proved immunogenic and efficacious in protecting against lethal monkeypox challenge, as evident from a lack of post-challenge viral replication, and the absence of any significant clinical signs attributable to monkeypox infection. This protection correlated (with) neutralizing antibody titers equivalent to those generated in the Dryvax group post-vaccination, as well as a similar significant increase in the presence of neutralizing antibodies post-challenge. Control animals showed no signs of vaccine-induced seroconversion, displayed post-challenge tissue-associated viral replication and viremia, and developed severe monkeypox-specific clinical symptoms. The protective efficacy of ACAM2000 was found to be equivalent to the currently approved vaccine, Dryvax.

Quantitation of CD8+ T cell responses to newly identified HLA-A*0201-restricted T cell epitopes conserved among vaccinia and variola (smallpox) viruses

Immunization with vaccinia virus resulted in long-lasting protection against smallpox and was the approach used to eliminate natural smallpox infections worldwide. Due to the concern about the potential use of smallpox virus as a bioweapon, smallpox vaccination is currently being reintroduced. Severe complications from vaccination were associated with congenital or acquired T cell deficiencies, but not with congenital agammaglobulinemia, suggesting the importance of T cell immunity in recovery from infection. In this report, we identified two CD8+ T cell epitopes restricted by the most common human major histocompatibility complex (MHC) class I allele, HLA-A*0201. Both epitopes are highly conserved in vaccinia and variola viruses. The frequency of vaccinia-specific CD8+ T cell responses to these epitopes measured by interferon (IFN)-gamma enzyme-linked immunospot (ELISPOT) assay and HLA/peptide tetramer staining peaked 2 wk after primary immunization and then declined, but were still detectable 1 to 3 yr after primary immunization. 2 wk after immunization, IFN-gamma-producing cells specific to these two epitopes were 14% of total vaccinia virus-specific IFN-gamma-producing cells in one donor, 35% in the second donor, and 6% in the third donor. This information will be useful for studies of human T cell memory and for the design and analyses of the immunogenicity of experimental vaccinia vaccines.