Performance assessment and validation of a plaque reduction neutralization test (PRNT) in support to yellow fever diagnostic and vaccine clinical trials.

Yellow fever (YF) virus is a mosquito-borne virus belonging to the Flaviviridae family that circulates in tropical and subtropical areas of Africa and South America. Despite the availability of an effective vaccine, YF remains a threat to travelers, residents of endemic areas, and unvaccinated populations. YF vaccination and natural infection both induce the production of neutralizing antibodies. Serological diagnostic methods detecting YF virus-specific antibodies demonstrate high levels of cross-reactivities with other flaviviruses. To date, the plaque reduction neutralization test (PRNT) is the most specific serological test for the differentiation of flavivirus infections and is considered the reference method for detecting YF neutralizing antibodies and assessing the protective immune response following vaccination. In this study, we developed and validated a YF PRNT. We optimized different parameters including cell concentration and virus-serum neutralization time period and then assessed the intra- and inter-assay precisions, dilutability, specificity, and lower limit of quantification (LLOQ) using international standard YF serum, sera from vaccinees and human specimens collected through YF surveillance. The YF PRNT has shown good robustness and 100% of intra-assay precision, 95.6% of inter-assay precision, 100% of specificity, 100% of LLOQ, and 95.3% of dilutability. The test is, therefore, suitable for use in the YF diagnostic as well as evaluation of the YF vaccine neutralizing antibody response and risk assessment studies.

Clinical Management of Yellow Fever in the Region of the Americas. Experiences and Recommendations for Health Services

The waves of yellow fever transmission in the Region of the Americas in 2016–2018 involved the largest number of human and epizootic cases to be reported in several decades. Yellow fever is a serious viral hemorrhagic disease that poses a challenge for health professionals. It requires early recognition of signs and symptoms, which are often nonspecific, and it can mimic other acute febrile syndromes. Early detection of suspected or confirmed cases, monitoring of vital signs, life support measures, and treatment of acute kidney failure continue to be the recommended strategies for case management. This report is the result of discussions among experienced specialists in the Americas on the clinical management of yellow fever patients, especially during outbreaks and epidemics, in the context of current medical and scientific evidence and taking into account the technical guidelines already available in the countries of the Region. It includes flowcharts for initially addressing patients with clinical suspicion of yellow fever and proposes a minimum package of laboratory tests that may be useful in contexts where resources are limited. In addition, it considers aspects of health system organization for dealing with yellow fever outbreaks and epidemics.

Manejo clínico de la fiebre amarilla en la Región de las Américas. Experiencias y recomendaciones para los servicios de salud

Las olas de transmisión de la fiebre amarilla ocurridas en la Región de las Américas entre el 2016 y el 2018 causaron el mayor número de casos humanos y epizoóticos registrados en varios decenios. La fiebre amarilla es una enfermedad hemorrágica viral grave que representa un desafío para el profesional de salud: exige el reconocimiento temprano de signos y síntomas muchas veces inespecíficos, que pueden parecerse a otros síndromes febriles agudos. La detección temprana de los casos sospechosos o confirmados, el monitoreo de los signos vitales y las medidas de soporte vital, y el tratamiento de la insuficiencia hepática aguda siguen siendo las estrategias recomendadas para el manejo de los casos. El presente informe es el resultado de las deliberaciones sobre la experiencia de expertos de la Región en cuanto al manejo clínico de pacientes con fiebre amarilla, especialmente en brotes y epidemias, mediante la contextualización de esa experiencia en el conjunto actual de la evidencia médico-científica y la consideración de las directrices técnicas ya disponibles en los países de la Región. Presenta flujogramas para la evaluación inicial del paciente con sospecha clínica de fiebre amarilla y sugiere un conjunto mínimo de pruebas de laboratorio que puede ser útil cuando hay pocos recursos; además, detalla aspectos de la organización de los sistemas de salud para enfrentar brotes y epidemias de fiebre amarilla.

A Globally Distributed Insecticide Resistance Allele Confers a Fitness Cost in the Absence of Insecticide in Aedes aegypti (Diptera: Culicidae), the Yellow Fever Mosquito.

The cosmopolitan mosquito Aedes aegypti is a vector of harmful arboviruses. Pyrethroid insecticides are used to reduce adult populations and prevent the spread of disease. Pyrethroids target the insect voltage-gated sodium channel (VGSC). Collectively, mutations in Vgsc that confer resistance are referred to as knock-down resistance or kdr. There are numerous kdr mutations found in A. aegypti Vgsc, and there is co-occurrence of some mutations. Full-length cDNA sequences have identified nine known kdr (e.g., 1534C) alleles. The 1534C allele is among the most common kdr alleles, but allele frequencies between populations vary considerably. We used the 1534C:RK strain, which has the 1534C (kdr) allele in the genetic background of the insecticide susceptible Rockefeller (ROCK) strain, and conducted population cage experiments to assess the potential intrinsic fitness cost of the 1534C allele relative to the susceptible allele (F1534) in the ROCK strain. Individuals were genotyped across generations using allele specific PCR. A fitness cost of the 1534C allele was detected across seven generations of mosquitos reared in the absence of insecticide selection pressure. The decrease in allele frequency was not due to drift. Comparison of our results to previous studies suggests that the magnitude of the fitness cost of kdr alleles in the absence of insecticide is disconnected from the level of resistance they confer, and that the fitness costs of different kdr alleles can be variable.

Manejo clínico da febre amarela na Região das Américas. Experiências e recomendações para os serviços de saúde

As ondas de transmissão de febre amarela (FA) ocorridas na Região das Américas de 2016 a 2018 envolveram o maior número de casos humanos e epizoóticos registrados em várias décadas. A febre amarela é uma doença hemorrágica viral grave que representa um desafio para o profissional de saúde: requer reconhecimento precoce de sinais e sintomas muitas vezes inespecíficos e que podem mimetizar outras síndromes febris agudas. A detecção precoce dos casos suspeitos ou confirmados, a monitorização de sinais vitais e as medidas de suporte de vida e terapêutica de manejo de insuficiência hepática aguda continuam sendo as estratégias recomendadas para o manejo dos casos. Este Informe é resultado das discussões de experiência de especialistas das Américas quanto ao manejo clínico de pacientes com febre amarela, especialmente em surtos e epidemias, contextualizando essa experiência no conjunto atual de evidências médico-científicas e considerando as diretrizes técnicas já disponíveis nos países da Região. Apresenta fluxogramas para a abordagem inicial do paciente com suspeita clínica de febre amarela e sugere um pacote de exames laboratoriais mínimos que pode ser útil em contextos com poucos recursos; ainda, detalha aspectos da organização dos sistemas de saúde para o enfrentamento de surtos e epidemias de febre amarela.

Risk assessment of urban yellow fever virus transmission in Kenya: is Aedes aegypti an efficient vector?

The absence of urban yellow fever epidemics in East Africa remains a mystery amidst the proliferation of Aedes aegypti in this region. To understand the transmission dynamics of the disease, we tested urban (Mombasa, Kisumu, and Nairobi) Aedes mosquito populations in Kenya for their susceptibility to an East African yellow fever virus (YFV) genotype. Overall, 22% (n = 805) of the Ae. aegypti that were orally challenged with an infectious dose of YFV had a midgut infection, with comparable rates for Mombasa and Kisumu (χ2 = 0.35, df = 1, P = 0.55), but significantly lower rates for Nairobi (χ2 ≥ 11.08, df = 1, P ≤ 0.0009). Variations in YFV susceptibility (midgut infection) among Ae. aegypti subspecies were not associated with discernable cytochrome c oxidase subunit 1 gene haplotypes. Remarkably, no YFV dissemination or transmission was observed among the orally challenged Ae. aegypti populations. Moreover, Ae. aegypti mosquitoes that were intrathoracically inoculated with YFV failed to transmit the virus via capillary feeding. In contrast, dissemination (oral exposure) and transmission (intrathoracic inoculation) of YFV was observed among a few peri-domestic Ae. bromeliae mosquitoes (n = 129) that were assessed from these urban areas. Our study highlights an inefficient urban Ae. aegypti population, and the potential for Ae. bromeliae in sustaining an urban YFV transmission in Kenya. An assessment of urban Ae. aegypti susceptibility to other YFV genotypes, and vector potential of urban Ae. bromeliae populations in Kenya is recommended to guide cost-effective vaccination.

FluoRNT: A robust, efficient assay for the detection of neutralising antibodies against yellow fever virus 17D.

There is an urgent need for better diagnostic and analytical methods for vaccine research and infection control in virology. This has been highlighted by recently emerging viral epidemics and pandemics (Zika, SARS-CoV-2), and recurring viral outbreaks like the yellow fever outbreaks in Angola and the Democratic Republic of Congo (2016) and in Brazil (2016-2018). Current assays to determine neutralising activity against viral infections in sera are costly in time and equipment and suffer from high variability. Therefore, both basic infection research and diagnostic population screenings would benefit from improved methods to determine virus-neutralising activity in patient samples. Here we describe a robust, objective, and scalable Fluorescence Reduction Neutralisation Test (FluoRNT) for yellow fever virus, relying on flow cytometric detection of cells infected with a fluorescent Venus reporter containing variant of the yellow fever vaccine strain 17D (YF-17D-Venus). It accurately measures neutralising antibody titres in human serum samples within as little as 24 h. Samples from 32 vaccinees immunised with YF-17D were tested for neutralising activity by both a conventional focus reduction neutralisation test (FRNT) and FluoRNT. Both types of tests proved to be equally reliable for the detection of neutralising activity, however, FluoRNT is significantly more precise and reproducible with a greater dynamic range than conventional FRNT. The FluoRNT assay protocol is substantially faster, easier to control, and cheaper in per-assay costs. FluoRNT additionally reduces handling time minimising exposure of personnel to patient samples. FluoRNT thus brings a range of desirable features that can accelerate and standardise the measurement of neutralising anti-yellow fever virus antibodies. It could be used in applications ranging from vaccine testing to large cohort studies in systems virology and vaccinology. We also anticipate the potential to translate the methodology and analysis of FluoRNT to other flaviviruses such as West Nile, Dengue and Zika or to RNA viruses more generally.

Analysis of yellow fever prevention strategy from the perspective of mathematical model and cost-effectiveness analysis.

We developed a new mathematical model for yellow fever under three types of intervention strategies: vaccination, hospitalization, and fumigation. Additionally, the side effects of the yellow fever vaccine were also considered in our model. To analyze the best intervention strategies, we constructed our model as an optimal control model. The stability of the equilibrium points and basic reproduction number of the model are presented. Our model indicates that when yellow fever becomes endemic or disappears from the population, it depends on the value of the basic reproduction number, whether it larger or smaller than one. Using the Pontryagin maximum principle, we characterized our optimal control problem. From numerical experiments, we show that the optimal levels of each control must be justified, depending on the strategies chosen to optimally control the spread of yellow fever.

An evaluation of the diagnostic performance characteristics of the Yellow Fever IgM immunochromatographic rapid diagnostic test kit from SD Biosensor in Ghana.

Yellow fever is endemic in Ghana and outbreaks occur periodically. The prodromal signs due to Yellow Fever Virus (YFV) infection are non-specific, making clinical signs unreliable as the sole criteria for diagnosis. Accurate laboratory confirmation of suspected yellow fever cases is therefore vital in surveillance programs. Reporting of ELISA IgM testing results by laboratories can delay due to late arrival of samples from the collection sites as well as limited availability of ELISA kits. In this study, the diagnostic performance characteristics of a rapid immunochromatographic Standard Q Yellow Fever IgM test kit (SD Biosensor) was evaluated for the rapid diagnosis of Yellow Fever infection in Ghana. A panel of 275 sera, comprising 81 confirmed YFV positives and 194 negatives were re-tested in this study using the Standard Q Yellow Fever IgM test kit. Using the CDC/WHO Yellow Fever IgM capture ELISA as a benchmark, the sensitivity, specificity and accuracy of the Standard Q Yellow Fever test kit were 96.3%, 97.9% and 97.5%, respectively. The false positivity rate was 5.1% and there was no cross-reactivity when the Standard Q Yellow Fever test kit was tested against dengue, malaria and hepatitis B and C positive samples. In addition, inter-reader variability and invalid rate were both zero. The results indicate that the diagnostic performance of the Standard Q Yellow Fever IgM test kit on serum or plasma is comparable to the serum IgM detection by ELISA and can be used as a point of care rapid diagnostic test kit for YFV infection in endemic areas.

[Yellow fever prevention and control: assessment of surveillance activities in a previously unaffected area in Brazil]. / Prevenção e controle da febre amarela: avaliação de ações de vigilância em área indene no Brasil.

Following the reemergence of yellow fever in 2014/2015, Brazil recorded its largest yellow fever epidemic in recent decades, mainly affecting the country's Southeast region. Yellow fever is a hemorrhagic viral disease caused by a flavivirus transmitted by sylvatic mosquitos (Haemagogus; Sabethes). In the urban cycle, eradicated in Brazil since 1942, the virus is transmitted by Aedes aegypti. Nonhuman primates are the principal hosts of the virus and constitute "sentinels" in yellow fever surveillance. This article describes the control and prevention activities launched during the yellow fever epidemic in the State of Espírito Santo, Brazil, and the implementation of vaccination, through an ecological study with a spatial approach. The study revealed the lack of detection of epizootics in nonhuman primates by surveillance services in Espírito Santo, with simultaneous detection in humans. The study presented the evolution of vaccination activities, reaching 85% overall coverage for the state in six months, varying widely, from 59% to 122%, between municipalities (counties). Importantly, 55% of the municipalities with timely immunization, considering the interval adopted for this study, did not present human cases. The intensification of surveillance activities, communication between areas, and multidisciplinary teams in managing the epidemic optimized the detection and diagnosis of human cases and allowed control of the epidemic. The study identifies progress and points to some late measures and gaps in surveillance that require improvements.

A partir da reemergência da febre amarela em 2014/2015, o Brasil registrou nos anos sequentes sua maior epidemia de febre amarela das últimas décadas, atingindo principalmente a região sudeste. A febre amarela, doença viral hemorrágica, é causada por um flavivírus, transmitido por mosquitos silvestres (Haemagogus; Sabethes). Na ocorrência do ciclo urbano, erradicado no Brasil desde 1942, a transmissão se dá pelo Aedes aegypti. Primatas não humanos são os principais hospedeiros do vírus e constituem "sentinelas" na vigilância da febre amarela. Este artigo descreve as ações de controle e prevenção desencadeadas durante a epidemia de febre amarela no Estado do Espírito Santo, Brasil, e a implementação da vacinação por meio de um estudo ecológico com abordagem espacial. O estudo evidenciou a falha na detecção de epizootias em primatas não humanos pelos serviços de vigilância do Espírito Santo, sendo simultânea à detecção em humanos. Apresentou a evolução das ações de vacinação, com alcance de 85% de cobertura vacinal geral para o estado em seis meses, sendo heterogênea entre os municípios (de 59% a 122%). Destaca-se que 55% dos municípios com ações de imunização em tempo oportuno, considerando o intervalo adotado para este estudo, não apresentaram casos em humanos. A intensificação das ações de vigilância, interlocução entre as áreas e equipes multidisciplinares na condução da epidemia otimizou a detecção e o diagnóstico dos casos em humanos e viabilizou o controle da epidemia. Foi possível reconhecer avanços, apontar algumas medidas tardias e lacunas na vigilância que necessitam melhorias.

A partir del resurgimiento de la fiebre amarilla en 2014/2015, Brasil registró los años siguientes su mayor epidemia de fiebre amarilla de las últimas décadas, alcanzando principalmente la región sudeste. La fiebre amarilla, enfermedad viral hemorrágica, es causada por un flavivirus, transmitido por mosquitos silvestres (Haemagogus; Sabethes). Respecto a la ocurrencia del ciclo urbano, erradicado en Brasil desde 1942, la transmisión se produce por el Aedes aegypti. Primates no humanos son los principales huéspedes del virus, y constituyen "centinelas" en la vigilancia de la fiebre amarilla. Este artículo describe las acciones de control y prevención desencadenadas durante la epidemia de fiebre amarilla en el Estado de Espírito Santo, Brasil, y la implementación de la vacunación mediante un estudio ecológico con abordaje espacial. El estudio evidenció el fallo en la detección de epizootias en primates no humanos por los servicios de vigilancia de Espírito Santo, siendo simultánea a la detección en humanos. Presentó la evolución de las acciones de vacunación, con alcance de un 85% de cobertura en la vacunación general para el estado en seis meses, siendo heterogénea entre los municipios (de 59% a 122%). Se destaca que un 55% de los municipios con acciones de inmunización en tiempo oportuno, considerando el intervalo adoptado para este estudio, no presentaron casos humanos. La intensificación de las acciones de vigilancia, interlocución entre las áreas y equipos multidisciplinarios en la gestión de la epidemia optimizó la detección y diagnóstico de los casos humanos y viabilizó el control de la epidemia. Fue posible reconocer avances, apuntar algunas medidas tardías y lagunas en la vigilancia que necesitan mejorías.

Inmunización en las Américas. Resumen 2021

Los países de las Américas, con apoyo de la Organización Panamericana de la Salud (OPS), han logrado avances notables al proporcionar a los niños y las niñas una protección general contra las enfermedades prevenibles mediante vacunación. Los niveles sostenidos de elevadas coberturas nacionales de vacunación, la erradicación de la poliomielitis, la interrupción de la transmisión endémica del virus del sarampión y las iniciativas más recientes en favor de la eliminación de la rubéola y el síndrome de rubéola congénita son hitos continentales de este progreso. En la actualidad, los países administran vacunas a grupos etarios distintos de los incluidos en los programas tradicionales de inmunización infantil. La introducción de la vacuna estacional contra la gripe en los adultos en riesgo; la vacunación de adolescentes y adultos, hombres y mujeres, para la eliminación de la rubéola, y la definición de la carga de enfermedad del cáncer cervicouterino son las actividades que apoyan la necesidad fundamental de efectuar una transición de los programas nacionales de inmunización infantil a programas de inmunización de la familia. Una de las funciones de la OPS en su apoyo a los países es difundir información que destaque el progreso de la Región y los desafíos que enfrenta. Con ese fin, publica varios documentos técnicos relacionados con la inmunización, tales como los boletines de inmunización, los módulos de capacitación en inmunización y la serie de guías prácticas sobre rubéola, sarampión, tétanos neonatal, poliomielitis, vacuna pentavalente y fiebre amarilla.

Prevenção e controle da febre amarela: avaliação de ações de vigilância em área indene no Brasil / Yellow fever prevention and control: assessment of surveillance activities in a previously unaffected area in Brazil / Prevención y control de la fiebre amarilla: evaluación de acciones de vigilancia en un área indemne de Brasil

A partir da reemergência da febre amarela em 2014/2015, o Brasil registrou nos anos sequentes sua maior epidemia de febre amarela das últimas décadas, atingindo principalmente a região sudeste. A febre amarela, doença viral hemorrágica, é causada por um flavivírus, transmitido por mosquitos silvestres (Haemagogus; Sabethes). Na ocorrência do ciclo urbano, erradicado no Brasil desde 1942, a transmissão se dá pelo Aedes aegypti. Primatas não humanos são os principais hospedeiros do vírus e constituem "sentinelas" na vigilância da febre amarela. Este artigo descreve as ações de controle e prevenção desencadeadas durante a epidemia de febre amarela no Estado do Espírito Santo, Brasil, e a implementação da vacinação por meio de um estudo ecológico com abordagem espacial. O estudo evidenciou a falha na detecção de epizootias em primatas não humanos pelos serviços de vigilância do Espírito Santo, sendo simultânea à detecção em humanos. Apresentou a evolução das ações de vacinação, com alcance de 85% de cobertura vacinal geral para o estado em seis meses, sendo heterogênea entre os municípios (de 59% a 122%). Destaca-se que 55% dos municípios com ações de imunização em tempo oportuno, considerando o intervalo adotado para este estudo, não apresentaram casos em humanos. A intensificação das ações de vigilância, interlocução entre as áreas e equipes multidisciplinares na condução da epidemia otimizou a detecção e o diagnóstico dos casos em humanos e viabilizou o controle da epidemia. Foi possível reconhecer avanços, apontar algumas medidas tardias e lacunas na vigilância que necessitam melhorias.

Following the reemergence of yellow fever in 2014/2015, Brazil recorded its largest yellow fever epidemic in recent decades, mainly affecting the country's Southeast region. Yellow fever is a hemorrhagic viral disease caused by a flavivirus transmitted by sylvatic mosquitos (Haemagogus; Sabethes). In the urban cycle, eradicated in Brazil since 1942, the virus is transmitted by Aedes aegypti. Nonhuman primates are the principal hosts of the virus and constitute "sentinels" in yellow fever surveillance. This article describes the control and prevention activities launched during the yellow fever epidemic in the State of Espírito Santo, Brazil, and the implementation of vaccination, through an ecological study with a spatial approach. The study revealed the lack of detection of epizootics in nonhuman primates by surveillance services in Espírito Santo, with simultaneous detection in humans. The study presented the evolution of vaccination activities, reaching 85% overall coverage for the state in six months, varying widely, from 59% to 122%, between municipalities (counties). Importantly, 55% of the municipalities with timely immunization, considering the interval adopted for this study, did not present human cases. The intensification of surveillance activities, communication between areas, and multidisciplinary teams in managing the epidemic optimized the detection and diagnosis of human cases and allowed control of the epidemic. The study identifies progress and points to some late measures and gaps in surveillance that require improvements.

A partir del resurgimiento de la fiebre amarilla en 2014/2015, Brasil registró los años siguientes su mayor epidemia de fiebre amarilla de las últimas décadas, alcanzando principalmente la región sudeste. La fiebre amarilla, enfermedad viral hemorrágica, es causada por un flavivirus, transmitido por mosquitos silvestres (Haemagogus; Sabethes). Respecto a la ocurrencia del ciclo urbano, erradicado en Brasil desde 1942, la transmisión se produce por el Aedes aegypti. Primates no humanos son los principales huéspedes del virus, y constituyen "centinelas" en la vigilancia de la fiebre amarilla. Este artículo describe las acciones de control y prevención desencadenadas durante la epidemia de fiebre amarilla en el Estado de Espírito Santo, Brasil, y la implementación de la vacunación mediante un estudio ecológico con abordaje espacial. El estudio evidenció el fallo en la detección de epizootias en primates no humanos por los servicios de vigilancia de Espírito Santo, siendo simultánea a la detección en humanos. Presentó la evolución de las acciones de vacunación, con alcance de un 85% de cobertura en la vacunación general para el estado en seis meses, siendo heterogénea entre los municipios (de 59% a 122%). Se destaca que un 55% de los municipios con acciones de inmunización en tiempo oportuno, considerando el intervalo adoptado para este estudio, no presentaron casos humanos. La intensificación de las acciones de vigilancia, interlocución entre las áreas y equipos multidisciplinarios en la gestión de la epidemia optimizó la detección y diagnóstico de los casos humanos y viabilizó el control de la epidemia. Fue posible reconocer avances, apuntar algunas medidas tardías y lagunas en la vigilancia que necesitan mejorías.

Regional Risk Assessment on Vaccine−Preventable Diseases (Diphteria, Measles, Yellow Fever, and Polio) in the Context of the COVID−19 Pandemic: Implications for the Region of the Americas (15 December 2021)

After more than 22 months of the ongoing COVID-19 pandemic in the Region of the Americas, and COVID-19 cases and deaths have been reported from all 56 countries and territories in the Region of the Americas, health systems are still being challenged and routine immunization activities are still behind in most of countries. The pandemic has affected compliance with the vaccine-preventable diseases (VPDs) surveillance indicators. Furthermore, imposed restrictions on movement as well as concerns due to the pandemic have limited primary healthcare activities, including preventive services such as vaccination, with a consequent decline in the vaccination coverage and an increase of the susceptible population. In addition, the migration phenomena in the Region, the relaxing of public health and social measures, and the impact of COVID-19 on the capacity of the healthcare systems, have led to challenges. Therefore, the occurrence of new outbreaks of VPDs of varying magnitude in the Americas Region cannot be ruled out, and the regional risk remains assessed as Very High.

Después de más de 22 meses de la pandemia de la COVID-19 en la Región de las Américas, se han notificado casos y muertes por COVID-19 en los 56 países y territorios de la Región de las Américas, los sistemas de salud aún enfrentan desafíos y las actividades de inmunización de rutina se están poniendo al día en la mayoría de los países. La pandemia ha afectado el cumplimiento de los indicadores de vigilancia de Enfermedades Prevenibles por Vacunas (EPV). Las restricciones impuestas a la circulación y la preocupación por la pandemia, han limitado las actividades de atención primaria de la salud, incluidos los servicios preventivos como la vacunación, con la consiguiente disminución de la cobertura de vacunación y un aumento de la población susceptible. A esto se suman, los fenómenos migratorios en la Región, el relajamiento de las medidas de salud pública y sociales, además del impacto de la COVID-19 en la capacidad de los sistemas de salud. Por lo tanto, no se puede descartar la ocurrencia de nuevos brotes de EPV de diversa magnitud en la Región de las Américas y el riesgo regional aún se evalúa como: Muy Alto.