The global landscape of smallpox vaccination history and implications for current and future orthopoxvirus susceptibility: a modelling study

Viral genomic features predict Orthopoxvirus reservoir hosts

Orthopoxviruses (OPVs), including the causative agents of smallpox and mpox have led to devastating outbreaks in human populations worldwide. However, the discontinuation of smallpox vaccination, which also provides cross-protection against related OPVs, has diminished global immunity to OPVs more broadly. We apply machine learning models incorporating both host ecological and viral genomic features to predict likely reservoirs of OPVs. We demonstrate that incorporating viral genomic features in addition to host ecological traits enhanced the accuracy of potential OPV host predictions, highlighting the importance of host-virus molecular interactions in predicting potential host species. We identify hotspots for geographic regions rich with potential OPV hosts in parts of southeast Asia, equatorial Africa, and the Amazon, revealing high overlap between regions predicted to have a high number of potential OPV host species and those with the lowest smallpox vaccination coverage, indicating a heightened risk for the emergence or establishment of zoonotic OPVs. Our findings can be used to target wildlife surveillance, particularly related to concerns about mpox establishment beyond its historical range.

Development and validation of a quantitative Orthopoxvirus immunoassay to evaluate and differentiate serological responses to Mpox infection and vaccination

BACKGROUND

The Mpox outbreak, caused by Monkeypox virus (MPXV), underscores the need for a serological assay to assess Mpox immunity. Modified Vaccinia Ankara (MVA) vaccine, an attenuated vaccinia virus (VACV), is authorised for Mpox prevention. We aimed to develop a quantitative immunoassay to differentiate infection- and vaccination-induced immunity and explore serological responses to Mpox infection and vaccination.

METHODS

We evaluated an electrochemiluminescence assay targeting IgG to 10 MPXV and 3 VACV antigens in plasma from adults in a cohort study with previous Mpox, MVA-vaccination, or historical controls. Sensitivity and specificity to distinguish i) seropositive versus naive and ii) infection- versus vaccination-induced seropositivity were determined using ROC curves. Antibody kinetics were analysed with generalised additive models.

FINDINGS

Eight of the thirteen IgG antibodies showed significant titre differences across groups identifying three key antigens: MPXVB6R, MPXVA27L, and VACVB5. A VACVB5 IgG titre of 0.082 IgG normalised units (nu) offered 74% (95% CI: 59-82%) sensitivity and 81% (73-96%) specificity for previous antigen exposure (infection or vaccine). For infection alone, an MPXVB6R IgG titre of 0.075 IgGnu provided 89% (82-98%) sensitivity and 94% (86-100%) specificity. To differentiate infection from vaccination-induced seropositivity, the sum of MPXVA27L IgG and the B6R/VACVB5 ratio provided 89% (80-96%) sensitivity and 80% (74-84%) specificity. VACVB5 IgG titres declined over time, with higher titres post-Mpox than post-vaccination (p < 0.0001).

INTERPRETATION

This assay demonstrates high sensitivity and specificity in quantifying and differentiating between antibody responses to Mpox infection and vaccination. Post-Mpox antibody responses were higher than post-vaccination, though both waned over time.

FUNDING

Health Research Board (MONKEYVAX-2022-1), University College Dublin School of Medicine.

Suspected and confirmed mpox cases in DR Congo: a retrospective analysis of national epidemiological and laboratory surveillance data, 2010-23

BACKGROUND

DR Congo has the highest global burden of mpox, a disease caused by infection with the monkeypox virus. The incidence has risen since 1980, but recent analyses of epidemiological trends are lacking. We aimed to describe trends in suspected and confirmed mpox cases in DR Congo using epidemiological and laboratory mpox surveillance data collected from 2010 to 2023, and provide insights that can better inform the targeting and monitoring of control strategies.

METHODS

We analysed aggregated national epidemiological surveillance data and individual-level laboratory data from 2010 to 2023. We calculated incidence based on suspected cases, case-fatality ratios, and percentage of laboratory-confirmed cases and assessed geospatial trends. Demographic and seasonal trends were investigated using generalised additive mixed models.

FINDINGS

Between Jan 1, 2010, and Dec 31, 2023, a total of 60 967 suspected cases and 1798 suspected deaths from mpox were reported in DR Congo (case-fatality ratio 2·9%). The number of reporting provinces increased from 18 of 26 provinces in 2010 to 24 of 26 provinces in 2023. The annual incidence increased from 2·97 per 100 000 in 2010 to 11·46 per 100 000 in 2023. The highest incidence (46·38 per 100 000) and case-fatality ratio (6·0%) were observed in children younger than 5 years. Incidence was higher in rural compared with urban areas. PCR testing was performed for 7438 suspected cases (12·2%), with 4248 (57·1%) of 7438 samples testing positive. Median age of confirmed cases (13·0 years [IQR 6·0-25·0]) remained stable, although the 95th percentile of age increased over time.

INTERPRETATION

The incidence and geographical distribution of suspected mpox cases have increased substantially since 2010. Improvements in surveillance and decentralised testing are essential to monitor mpox trends and direct interventions effectively, to address the public health emergency declarations issued in August, 2024.

FUNDING

Belgian Directorate-General Development Cooperation and Humanitarian Aid; European and Developing Countries Clinical Trials Partnership; Research Foundation-Flanders; European Civil Protection and Humanitarian Aid Operations; Department of Economy, Science, and Innovation of the Flemish Government; Canadian Institutes of Health Research; and the International Development Research Centre.

Domestic Dogs Exposed to Orthopoxvirus in Urban Areas of Brazil

Domestic animals can share viral pathogens with humans, acting mainly as a bridge host. The Orthopoxvirus genus hosts important zoonotic species that have emerged in urban areas worldwide. Nevertheless, the role of companion animals, such as dogs and cats, in the circulation of orthopoxviruses in urban areas remains poorly understood. Therefore, the objective of this study was to evaluate the presence of neutralizing anti-orthopoxvirus antibodies in serum samples from owned dogs from three municipalities in Minas Gerais, as well as the presence of the C11R and A56R orthopoxviruses genes. The presence of neutralizing antibodies was detected in 14.3% of the animals investigated. However, no sample was positive for the presence of the genes investigated. Further study of the population of dogs in urban areas may prove a valuable tool for understanding the spread of orthopoxviruses in urbanized areas of Brazil.

The Rise of Mpox in a Post-Smallpox World

Reports of mpox are rising in Africa where the disease is endemic and in new countries where the disease has not been previously seen. The 2022 global outbreak of clade II mpox and an ongoing outbreak of the more lethal clade I mpox highlight the pandemic potential for monkeypox virus. Waning population immunity after the cessation of routine immunization for smallpox plays a key role in the changing epidemiologic patterns of mpox. Sustained human-to-human transmission of mpox is occurring widely in the context of insufficient population immunity, fueling genetic mutations that affect the accuracy of some diagnostic tests and that could lead to changing virulence. Additional research should address complex challenges for control of mpox, including improved diagnostics and medical countermeasures. The availability of vaccines should be expanded not only for outbreak response but also for broader routine use for persons in mpox-endemic countries.

Elderly Individuals Exhibit Elevated Levels of Anti-Monkeypox Virus Antibodies Compared to Adults, Youth, and Children

The variola virus, the causative agent of smallpox, has claimed more human lives than all other infectious diseases combined. Consequently, any epidemiological event involving related viruses (orthopoxviruses) triggers significant concern, as was the case with the pandemic rise of monkeypox virus (MPXV), the causative agent of monkeypox in 2022-2023. Smallpox vaccines, based on vaccinia virus antigens, are expected to provide cross-protection against MPXV. Studying the general seroprevalence of orthopoxviruses in populations worldwide is crucial for estimating susceptibility, risks, and the need for vaccination campaigns. In this study, we aimed to evaluate the seroprevalence of antibodies capable of recognizing MPXV in a Brazilian population and assess the potential for cross-protection from previous smallpox vaccinations. We analyzed demographic data, vaccination records, and serum levels of anti-MPXV IgG measured by enzyme-linked immunosorbent assay (ELISA) in 319 volunteers from Barreiras, Bahia, Brazil. Our main findings show that the numbers of volunteers with serum samples recognizing MPXV in ELISA, as well as their serum levels of anti-MPXV IgG, did not differ significantly according to gender or address type. However, both male and female elderly volunteers exhibited significantly higher concentrations of anti-MPXV IgG than adults, youth, and children. These results suggest that the elderly may benefit from a cross-reactive immune response due to previous smallpox vaccinations, whereas adults, youth, and children appear susceptible to MPXV. Further investigations involving other populations are necessary to assess the necessity of vaccinating potentially vulnerable groups.

The Peculiar Emergence of Mpox (Monkeypox): Directions for the Search for the Natural Reservoir and Vaccination Strategies

Background/Objectives: Mpox (monkeypox) is a zoonosis with origins in a currently unknown African reservoir. The first epidemiological accounts of mpox date back to the early 1980s, yet mpox only emerged as a pandemic threat in 2022-2023, more than 40 years later. This scenario is very different from those of other emerging diseases such as HIV and SARS, which immediately spread globally, in fully susceptible populations, starting from patients zero. Methods: We use mathematical modeling to illustrate the dynamics of mpox herd immunity in small communities in touch with the mpox natural reservoir. In particular, we employ an SEIR stochastic model. Results: The peculiar emergence of mpox can be explained by its relationship with smallpox, which was eradicated through universal mass vaccination in 1980. Mpox first emerged in small rural communities in touch with mpox's animal reservoir and then spread globally. The relative isolation of these communities and their herd-immunity dynamics against mpox worked to delay the introduction of mpox in large urban centers. Conclusions: Mathematical modeling suggests that the search for the mpox animal reservoir would be most fruitful in communities with high mpox seroprevalence and small outbreaks. These are communities is tight contact with the mpox natural reservoir. We propose vaccinating individuals in communities in these communities to severely reduce the importation of cases elsewhere.

Monkeypox in Bulgaria: Significance of Various Clinical Samples, Clinical Manifestation, and Molecular Detection

Background/Objectives: Monkeypox (mpox) is currently the most common orthopoxvirus (OPXV) zoonotic disease, and, since 2022, there has been atypical person-to-person transmission observed in non-endemic countries. The present study aimed to investigate the frequency of monkeypox virus (MPXV) and OPXV DNA detection in recommended and alternative clinical materials taken during the acute and convalescent phases of infection in Bulgarian patients. Methods: The study included laboratory investigation by real time PCR of 181 clinical samples from 42 Bulgarian patients with possible mpox infections. Results: MPXV DNA was detected in 23/181 (12.71%), and OPXV DNA in 20/181 (11.05%) clinical samples. There were six mpox-confirmed patients aged 23 to 44. At the highest frequency, MPXV and OPXV DNA were detected in samples of vesicular contents (6/6) and nasal/oropharyngeal secretions (5/6 and 4/6) during the first three days from the appearance of clinical symptoms. We demonstrated MPXV and OPXV DNA in alternative samples (urine, feces, ejaculate, and saliva), and in follow-up patient samples, taken two weeks after mpox confirmation in the convalescent phase (vesicular contentsand urine). Conclusions: Our findings suggested that MPXV may be detected in a larger set of clinical materials, including alternatives, where the virus can persist for more than two weeks.

Effectiveness of historical smallpox vaccination against mpox clade II in men in Denmark, France, the Netherlands and Spain, 2022

BackgroundIn 2022, a global monkeypox virus (MPXV) clade II epidemic occurred mainly among men who have sex with men. Until early 1980s, European smallpox vaccination programmes were part of worldwide smallpox eradication efforts. Having received smallpox vaccine > 20 years ago may provide some cross-protection against MPXV.AimTo assess the effectiveness of historical smallpox vaccination against laboratory-confirmed mpox in 2022 in Europe.MethodsEuropean countries with sufficient data on case vaccination status and historical smallpox vaccination coverage were included. We selected mpox cases born in these countries during the height of the national smallpox vaccination campaigns (latest 1971), male, with date of onset before 1 August 2022. We estimated vaccine effectiveness (VE) and corresponding 95% CI for each country using logistic regression as per the Farrington screening method. We calculated a pooled estimate using a random effects model.ResultsIn Denmark, France, the Netherlands and Spain, historical smallpox vaccination coverage was high (80-90%) until the end of the 1960s. VE estimates varied widely (40-80%, I2 = 82%), possibly reflecting different booster strategies. The pooled VE estimate was 70% (95% CI: 23-89%).ConclusionOur findings suggest residual cross-protection by historical smallpox vaccination against mpox caused by MPXV clade II in men with high uncertainty and heterogeneity. Individuals at high-risk of exposure should be offered mpox vaccination, following national recommendations, regardless of prior smallpox vaccine history, until further evidence becomes available. There is an urgent need to conduct similar studies in sub-Saharan countries currently affected by the MPXV clade I outbreak.

Factors potentially contributing to the decline of the mpox outbreak in the Netherlands, 2022 and 2023

BackgroundIn 2022 and 2023, a global outbreak of mpox affected mostly gay, bisexual and other men having sex with men (GBMSM). Outbreak control in the Netherlands included isolation, quarantine, post-exposure prophylaxis vaccination and primary preventive vaccination (PPV).AimWe describe the course of the outbreak, the vaccination programme, vaccine effectiveness (VE) of full vaccination against symptomatic disease, and trends in behaviour to generate hypotheses about factors that influenced the outbreak's decline.MethodsIn this observational study, we collected data from public health services on notified cases, number of PPV invitations and PPV doses administered. We calculated PPV uptake and coverage. Trends in behavioural data of GBMSM visiting sexual health centres were analysed for all consultations in 2022. We estimated VE using the screening method.ResultsUntil 31 December 2023, 1,294 mpox cases were reported. The outbreak peaked in early July 2022 and then declined sharply. PPV started on 25 July 2022; in total 29,851 doses were administered, 45.8% received at least one dose, 35.4% were fully vaccinated. The estimated VE was 68.2% (95% CI 4.3-89.5%). We did not observe an evident decrease in high-risk behaviour.DiscussionIt is unlikely that PPV was a driver of the outbreak's decline, as incidence started to decline well before the start of the PPV programme. The possible impact of behavioural change could not be demonstrated with the available indicators, however, the data had limitations, hampering interpretation. We hypothesise that infection-induced immunity in high-risk groups was an important factor explaining the decline.

Tracing the journey of poxviruses: insights from history

The historical significance of the poxviruses is profound, largely due to the enduring impact left by smallpox virus across many centuries. The elimination of smallpox is a remarkable accomplishment in the history of science and medicine, with centuries of devoted efforts resulting in the development and widespread administration of smallpox vaccines. This review provides insight into the pivotal historical events involving medically significant poxviruses. Understanding the remarkable saga of combatting smallpox is crucial, serving as a guidepost for potential future encounters with poxvirus infections. There is a continual need for vigilant observation of poxvirus evolution and spillover from animals to humans, considering the expansive range of susceptible hosts. The recent occurrence of monkeypox cases in non-endemic countries stands as a stark reminder of the ease with which infections can be disseminated through international travel and trade. This backdrop encourages introspection about our journey and the current status of poxvirus research.

Unexpectedly higher levels of anti-orthopoxvirus neutralizing antibodies are observed among gay men than general adult population

BACKGROUND

The confirmed cases in the current outbreak of Monkeypox are predominantly identified in the networks of men who have sex with men (MSM). The preexisting antibodies may profoundly impact the transmission of monkeypox virus (MPXV), however the current-day prevalence of antibodies against MPXV among gay men is not well characterized.

METHODS

A cohort of gay men (n = 326) and a cohort of the general adult population (n = 295) were enrolled in this study. Binding antibodies responses against MPXV/vaccinia and neutralizing antibody responses against vaccinia virus (Tiantan strain) were measured. The antibody responses of these two cohorts were then compared, as well as the responses of individuals born before and in/after 1981 (when the smallpox vaccination ceased in China). Finally, the correlation between the anti-MPXV antibody responses and the anti-vaccinia antibody responses, and the associations between preexisting anti-orthopoxvirus antibody responses and the diagnosed sexually transmitted infections (STIs) in the MSM cohort were analyzed separately.

RESULTS

Our data showed that binding antibodies against MPXV H3, A29, A35, E8, B6, M1 proteins and vaccinia whole-virus lysate could be detected in individuals born both before and in/after 1981, of which the prevalence of anti-vaccinia binding antibodies was significantly higher among individuals born before 1981 in the general population cohort. Moreover, we unexpectedly found that the positive rates of binding antibody responses against MPXV H3, A29, A35, E8 and M1 proteins were significantly lower among individuals of the MSM cohort born in/after 1981, but the positive rates of anti-MPXV B6 and anti-vaccinia neutralizing antibody responses were significantly higher among these individuals compared to those of age-matched participants in the general population cohort. Additionally, we demonstrated that the positive and negative rates of anti-MPXV antibody responses were associated with the anti-vaccinia antibody responses among individuals born before 1981 in the general population cohort, but no significant association was observed among individuals born in/after 1981 in both cohorts. The positive rates of both the binding and the neutralizing antibody responses were comparable between individuals with and without diagnosed STIs in the MSM cohort.

CONCLUSIONS

Anti-MPXV and anti-vaccinia antibodies could be readily detected in an MSM cohort and a general population cohort. And a higher level of anti-vaccinia neutralizing antibody responses was observed among individuals who did not get vaccinated against smallpox in the MSM cohort compared to age-matched individuals in the general population cohort.

Human Monkeypox-A Global Public Health Emergency

Monkeypox, a viral zoonosis caused by an Orthopoxvirus, is clinically characterized by fever, headache, lymphadenopathy, myalgia, rash and burdened by some complications that can be severe and life threatening. Monkeypox, endemic in some central and west African countries, in tropical areas near equator, rose to the headlines following its recent outbreak in non-endemic countries of Europe and the USA. Thus, the World Health Organization, worried about the growing dimension of the problem, declared monkeypox a global public health emergency. Now, after months of careful observation, the western scientific research is drawing conclusion that African endemic countries represent a reserve pool able to feed, through travelers and sexual networks, the outbreak in non-endemic countries in which high-risk communities such as gay and bisexual men are the most affected. Prevention through vaccination and early diagnosis are the core to breaking the chain of diffusion of this epidemic. Particular attention should be paid to avoid the spread from endemic countries, also implementing the economic investments in their public health system. Information campaigns and assistance to high-risk classes in non-endemic countries are important priorities, however, assuming that specific treatments for this disease are still tentative.