Measles and the canonical path to elimination

Spatial scales of COVID-19 transmission in Mexico

During outbreaks of emerging infectious diseases, internationally connected cities often experience large and early outbreaks, while rural regions follow after some delay. This hierarchical structure of disease spread is influenced primarily by the multiscale structure of human mobility. However, during the COVID-19 epidemic, public health responses typically did not take into consideration the explicit spatial structure of human mobility when designing nonpharmaceutical interventions (NPIs). NPIs were applied primarily at national or regional scales. Here, we use weekly anonymized and aggregated human mobility data and spatially highly resolved data on COVID-19 cases at the municipality level in Mexico to investigate how behavioral changes in response to the pandemic have altered the spatial scales of transmission and interventions during its first wave (March-June 2020). We find that the epidemic dynamics in Mexico were initially driven by exports of COVID-19 cases from Mexico State and Mexico City, where early outbreaks occurred. The mobility network shifted after the implementation of interventions in late March 2020, and the mobility network communities became more disjointed while epidemics in these communities became increasingly synchronized. Our results provide dynamic insights into how to use network science and epidemiological modeling to inform the spatial scale at which interventions are most impactful in mitigating the spread of COVID-19 and infectious diseases in general.

Possible Paths to Measles Eradication: Conceptual Frameworks, Strategies, and Tactics

Measles elimination refers to the interruption of measles virus transmission in a defined geographic area (e.g., country or region) for 12 months or more, and measles eradication refers to the global interruption of measles virus transmission. Measles eradication was first discussed and debated in the late 1960's shortly after the licensure of measles vaccines. Most experts agree that measles meets criteria for disease eradication, but progress toward national and regional measles elimination has slowed. Several paths to measles eradication can be described, including an incremental path through country-wide and regional measles elimination and phased paths through endgame scenarios and strategies. Infectious disease dynamic modeling can help inform measles elimination and eradication strategies, and all paths would be greatly facilitated by innovative technologies such as microarray patches to improve vaccine access and demand, point-of-contact diagnostic tests to facilitate outbreak responses, and point-of-contact IgG tests to identify susceptible populations. A pragmatic approach to measles eradication would identify and realize the necessary preconditions and clearly articulate various endgame scenarios and strategies to achieve measles eradication with an intensified and coordinated global effort in a specified timeframe, i.e., to "go big and go fast". To encourage and promote deliberation among a broad array of stakeholders, we provide a brief historical background and key considerations for setting a measles eradication goal.

Congenital Rubella Syndrome Does Not Increase with Introduction of Rubella-Containing Vaccine

Rubella infection is typically mild or asymptomatic except when infection occurs during pregnancy. Infection in early pregnancy can cause miscarriage, stillbirth, or congenital rubella syndrome. Only individuals that are still susceptible to rubella infection during child-bearing age are vulnerable to this burden. Rubella-containing vaccine (RCV) is safe and effective, providing life-long immunity. However, average age-at-infection increases with increasing vaccination coverage, which could potentially lead to increased disease burden if the absolute risk of infection during child-bearing age increases. The dynamics of rubella transmission were explored using EMOD, a software tool for building stochastic, agent-based infection models. Simulations of pre-vaccine, endemic transmission of rubella virus introduced RCV at varying levels of coverage to determine the expected future trajectories of disease burden. Introducing RCV reduces both rubella virus transmission and disease burden for a period of around 15 years. Increased disease burden is only possible more than a decade post-introduction, and only for contexts with persistently high transmission intensity. Low or declining rubella virus transmission intensity is associated with both greater burden without vaccination and greater burden reduction with vaccination. The risk of resurgent burden due to incomplete vaccination only exists for locations with persistently high infectivity, high connectivity, and high fertility. A trade-off between the risk of a small, future burden increase versus a large, immediate burden decrease strongly favors RCV introduction.

Epidemiology of confirmed measles virus cases, surveillance, incidence, and associated factors in Eritrea: 18-year retrospective analysis

Background

Despite the outstanding measles vaccine coverage (MVC) in Eritrea, sporadic outbreaks are not uncommon. Therefore, understanding the incidence of laboratory-confirmed measles virus cases, related factors, and spatial inequalities in testing and surveillance remains crucial. In this analysis, we evaluated the incidence and spatiotemporal distribution of measles in Eritrea. An evaluation of the factors associated with measles vaccination and IgM positive (+) febrile rash was also undertaken.

Methods

A retrospective (period: 2002-2020) study was carried out by abstracting data from the integrated disease surveillance and response database (IDSR). Data was analyzed using descriptive statistics and binary logistic regression. Spatial variability and distribution of confirmed cases was evaluated using ArcGIS Pro version 3.0.1.

Results

In total, 9,111 suspected cases, 2,767 [1,431 (51.7%) females] were serologically tested. The median (IQR) age, minimum-maximum age were 7 years (IQR: 4-14 years) and 1 month-97 years, respectively. Among the 608(21.9%) laboratory-confirmed cases, 534 (87.8%) were unvaccinated and 53 (9.92%) were < 1 year old. The crude incidence rate for MV was 14/100,000 persons. The age-specific positivity rate per 100,000 suspected cases tested was 21.5 with individuals >30 years presenting with the highest rates (69.9/100,000). Higher odds (OR) of MV test positivity was associated with age at onset - higher in the following age-bands [10-14 years: OR = 1.6 (95%CI, 1.1-2.2, value of p = 0.005); 15-29 years: OR = 7.0 (95%CI, 5.3-9.2, value of p = 0.005); and > =30 years: OR = 16.7 (95%CI, 11.7-24) p < 0.001]. Other associations included: Address - higher in Anseba (OR = 2.3, 95%CI: 1.7-3.1, value of p<0.001); Debub (OR = 2.7, 95%CI: 1.9-3.9, value of p < 0.001); Gash-Barka (OR = 15.4, 95%CI: 10.9-21.7, value of p < 0.001); Northern Red Sea (OR = 11.8, 95%CI: 8.5-16.2, value of p < 0.001); and Southern Red Sea (OR = 14.4, 95%CI: 8.2-25.2, value of p < 0.001). Further, test positivity was higher in health centers (OR = 2.5, 95%CI: 1.9-3.4, value of p < 0.001) and hospitals (OR = 6.8, 95%CI: 5.1-9.1, value of p < 0.001). Additional factors included vaccination status - higher in the unvaccinated (OR = 14.7, 95%CI: 11.4-19.1, value of p < 0.001); and year of onset of rash - (higher >2015: OR = 1.4, 95%CI: 1.1-1.7, value of p<0.001). Uptake of measles vaccine associated with a similar complement of factors.

Conclusion

In large part, efforts to eliminate measles in Eritrea are hindered by disparities in vaccine coverage, under-surveillance, and low vaccination rates in neighboring countries. Enhanced surveillance and regional micro planning targeting hard-to-reach areas can be an effective strategy to improve measles elimination efforts in Eritrea.

Feasibility of measles and rubella vaccination programmes for disease elimination: a modelling study

Background

Marked reductions in the incidence of measles and rubella have been observed since the widespread use of the measles and rubella vaccines. Although no global goal for measles eradication has been established, all six WHO regions have set measles elimination targets. However, a gap remains between current control levels and elimination targets, as shown by large measles outbreaks between 2017 and 2019. We aimed to model the potential for measles and rubella elimination globally to inform a WHO report to the 73rd World Health Assembly on the feasibility of measles and rubella eradication.

Methods

In this study, we modelled the probability of measles and rubella elimination between 2020 and 2100 under different vaccination scenarios in 93 countries of interest. We evaluated measles and rubella burden and elimination across two national transmission models each (Dynamic Measles Immunisation Calculation Engine [DynaMICE], Pennsylvania State University [PSU], Johns Hopkins University, and Public Health England models), and one subnational measles transmission model (Institute for Disease Modeling model). The vaccination scenarios included a so-called business as usual approach, which continues present vaccination coverage, and an intensified investment approach, which increases coverage into the future. The annual numbers of infections projected by each model, country, and vaccination scenario were used to explore if, when, and for how long the infections would be below a threshold for elimination.

Findings

The intensified investment scenario led to large reductions in measles and rubella incidence and burden. Rubella elimination is likely to be achievable in all countries and measles elimination is likely in some countries, but not all. The PSU and DynaMICE national measles models estimated that by 2050, the probability of elimination would exceed 75% in 14 (16%) and 36 (39%) of 93 modelled countries, respectively. The subnational model of measles transmission highlighted inequity in routine coverage as a likely driver of the continuance of endemic measles transmission in a subset of countries.

Interpretation

To reach regional elimination goals, it will be necessary to innovate vaccination strategies and technologies that increase spatial equity of routine vaccination, in addition to investing in existing surveillance and outbreak response programmes.

Funding

WHO, Gavi, the Vaccine Alliance, US Centers for Disease Control and Prevention, and the Bill & Melinda Gates Foundation.

Prioritizing COVID-19 vaccination efforts and dose allocation within Madagascar

Background

While mass COVID-19 vaccination programs are underway in high-income countries, limited availability of doses has resulted in few vaccines administered in low and middle income countries (LMICs). The COVID-19 Vaccines Global Access (COVAX) is a WHO-led initiative to promote vaccine access equity to LMICs and is providing many of the doses available in these settings. However, initial doses are limited and countries, such as Madagascar, need to develop prioritization schemes to maximize the benefits of vaccination with very limited supplies. There is some consensus that dose deployment should initially target health care workers, and those who are more vulnerable including older individuals. However, questions of geographic deployment remain, in particular associated with limits around vaccine access and delivery capacity in underserved communities, for example in rural areas that may also include substantial proportions of the population.

Methods

To address these questions, we developed a mathematical model of SARS-CoV-2 transmission dynamics and simulated various vaccination allocation strategies for Madagascar. Simulated strategies were based on a number of possible geographical prioritization schemes, testing sensitivity to initial susceptibility in the population, and evaluating the potential of tests for previous infection.

Results

Using cumulative deaths due to COVID-19 as the main outcome of interest, our results indicate that distributing the number of vaccine doses according to the number of elderly living in the region or according to the population size results in a greater reduction of mortality compared to distributing doses based on the reported number of cases and deaths. The benefits of vaccination strategies are diminished if the burden (and thus accumulated immunity) has been greatest in the most populous regions, but the overall strategy ranking remains comparable. If rapid tests for prior immunity may be swiftly and effectively delivered, there is potential for considerable gain in mortality averted, but considering delivery limitations modulates this.

Conclusion

At a subnational scale, our results support the strategy adopted by the COVAX initiative at a global scale.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12889-022-13150-8.

Dissecting recurrent waves of pertussis across the boroughs of London

Pertussis has resurfaced in the UK, with incidence levels not seen since the 1980s. While the fundamental causes of this resurgence remain the subject of much conjecture, the study of historical patterns of pathogen diffusion can be illuminating. Here, we examined time series of pertussis incidence in the boroughs of Greater London from 1982 to 2013 to document the spatial epidemiology of this bacterial infection and to identify the potential drivers of its percolation. The incidence of pertussis over this period is characterized by 3 distinct stages: a period exhibiting declining trends with 4-year inter-epidemic cycles from 1982 to 1994, followed by a deep trough until 2006 and the subsequent resurgence. We observed systematic temporal trends in the age distribution of cases and the fade-out profile of pertussis coincident with increasing national vaccine coverage from 1982 to 1990. To quantify the hierarchy of epidemic phases across the boroughs of London, we used the Hilbert transform. We report a consistent pattern of spatial organization from 1982 to the early 1990s, with some boroughs consistently leading epidemic waves and others routinely lagging. To determine the potential drivers of these geographic patterns, a comprehensive parallel database of borough-specific features was compiled, comprising of demographic, movement and socio-economic factors that were used in statistical analyses to predict epidemic phase relationships among boroughs. Specifically, we used a combination of a feed-forward neural network (FFNN), and SHapley Additive exPlanations (SHAP) values to quantify the contribution of each covariate to model predictions. Our analyses identified a number of predictors of a borough's historical epidemic phase, specifically the age composition of households, the number of agricultural and skilled manual workers, latitude, the population of public transport commuters and high-occupancy households. Univariate regression analysis of the 2012 epidemic identified the ratio of cumulative unvaccinated children to the total population and population of Pakistan-born population to have moderate positive and negative association, respectively, with the timing of epidemic. In addition to providing a comprehensive overview of contemporary pertussis transmission in a large metropolitan population, this study has identified the characteristics that determine the spatial spread of this bacterium across the boroughs of London.

Measles

Measles is a highly contagious, potentially fatal, but vaccine-preventable disease caused by measles virus. Symptoms include fever, maculopapular rash, and at least one of cough, coryza, or conjunctivitis, although vaccinated individuals can have milder or even no symptoms. Laboratory diagnosis relies largely on the detection of specific IgM antibodies in serum, dried blood spots, or oral fluid, or the detection of viral RNA in throat or nasopharyngeal swabs, urine, or oral fluid. Complications can affect many organs and often include otitis media, laryngotracheobronchitis, pneumonia, stomatitis, and diarrhoea. Neurological complications are uncommon but serious, and can occur during or soon after the acute disease (eg, acute disseminated encephalomyelitis) or months or even years later (eg, measles inclusion body encephalitis and subacute sclerosing panencephalitis). Patient management mainly involves supportive therapy, such as vitamin A supplementation, monitoring for and treatment of secondary bacterial infections with antibiotics, and rehydration in the case of severe diarrhoea. There is no specific antiviral therapy for the treatment of measles, and disease control largely depends on prevention. However, despite the availability of a safe and effective vaccine, measles is still endemic in many countries and causes considerable morbidity and mortality, especially among children in resource-poor settings. The low case numbers reported in 2020, after a worldwide resurgence of measles between 2017 and 2019, have to be interpreted cautiously, owing to the effect of the COVID-19 pandemic on disease surveillance. Disrupted vaccination activities during the pandemic increase the potential for another resurgence of measles in the near future, and effective, timely catch-up vaccination campaigns, strong commitment and leadership, and sufficient resources will be required to mitigate this threat.

Infectious disease in an era of global change

The twenty-first century has witnessed a wave of severe infectious disease outbreaks, not least the COVID-19 pandemic, which has had a devastating impact on lives and livelihoods around the globe. The 2003 severe acute respiratory syndrome coronavirus outbreak, the 2009 swine flu pandemic, the 2012 Middle East respiratory syndrome coronavirus outbreak, the 2013-2016 Ebola virus disease epidemic in West Africa and the 2015 Zika virus disease epidemic all resulted in substantial morbidity and mortality while spreading across borders to infect people in multiple countries. At the same time, the past few decades have ushered in an unprecedented era of technological, demographic and climatic change: airline flights have doubled since 2000, since 2007 more people live in urban areas than rural areas, population numbers continue to climb and climate change presents an escalating threat to society. In this Review, we consider the extent to which these recent global changes have increased the risk of infectious disease outbreaks, even as improved sanitation and access to health care have resulted in considerable progress worldwide.

Examination of scenarios introducing rubella vaccine in the Democratic Republic of the Congo

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Serosurvey data suggest R₀ values for rubella in the DRC on the range 3 to 8.

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Supplementary immunization activities provide multi-decade reduction in burden.

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Post-vaccine introduction, burden will likely be concentrated in outbreaks.

Background

Rubella vaccine has yet to be introduced into the national immunization schedule of the Democratic Republic of the Congo (DRC); the current burden of congenital rubella syndrome (CRS) is unknown and likely to be high. An important consideration prior to introducing rubella containing vaccine (RCV) is the potential inverse relationship between RCV coverage and CRS incidence. Increasing RCV coverage will also increase in the average age of infection. Cumulative infections across all age groups will decrease, but the number of infections in age groups vulnerable to CRS may increase.

Methods

Rubella transmission dynamics in the DRC were simulated using a stochastic agent-based model of transmission. Input parameter values for known properties, demographic variables, and interventions were fixed; infectivity was inferred from seropositivity profiles in survey data.

Results

Our simulations of RCV introduction for the DRC demonstrate that an increase in CRS burden is unlikely. Continued endemic transmission is only plausible when routine immunization coverage is less than 40% and follow-up supplemental immunization activities have poor coverage for decades.

Conclusion

Increased vaccination coverage tends to increase the annual variability of CRS burden. Simulations examining low vaccination coverage and high mean CRS burden are outbreak prone, with multiple years of reduced burden followed by acute outbreaks. These outcomes contrast simulations with no vaccination coverage and high mean CRS burden, which have more consistent burden from year to year.

Challenges in evaluating risks and policy options around endemic establishment or elimination of novel pathogens

When a novel pathogen emerges there may be opportunities to eliminate transmission - locally or globally - whilst case numbers are low. However, the effort required to push a disease to elimination may come at a vast cost at a time when uncertainty is high. Models currently inform policy discussions on this question, but there are a number of open challenges, particularly given unknown aspects of the pathogen biology, the effectiveness and feasibility of interventions, and the intersecting political, economic, sociological and behavioural complexities for a novel pathogen. In this overview, we detail how models might identify directions for better leveraging or expanding the scope of data available on the pathogen trajectory, for bounding the theoretical context of emergence relative to prospects for elimination, and for framing the larger economic, behavioural and social context that will influence policy decisions and the pathogen’s outcome.

Current understandings of the impact of mandatory vaccination laws in Europe

Vaccinations are among the most successful preventive tools to protect collective health. In response to alarming vaccines preventable diseases (VPDs) outbreaks resurgence, decreased vaccination coverage and vaccine refusal, several European countries have recently revised their vaccination policies introducing or extending mandatory vaccinations. This review examines the health, political and ethical aspects of mandatory vaccination.The authors first clarify terms and definitions and propose a conceptual framework of mandatory policies. Second, they describe the current status of mandatory childhood immunization programmes in Europe, assessing selected mandatory laws. Third, as the authors conduct a systematic review of the literature (retrieving from Medline 17 relevant records between 2010 and 2020), they take an analytical approach to measure the impact of mandatory vaccination policies on both VPDs control and immunization coverage, but also on population attitudes toward vaccines. 40% of European countries currently have mandatory vaccination policies; however, policies vary widely and, although there is evidence of increased vaccine uptake, their impact on informed adherence to preventive behaviors is scant.Although mandatory vaccination policies might be needed to protect collective health in times of emergency, public health goals of VPD prevention and health promotion should primarily be pursued through health education and population empowerment.

Feasibility assessment of measles and rubella eradication

This report addresses the epidemiological aspects and feasibility of measles and rubella eradication and the potential resource requirements in response to the request of the Director-General at the Seventieth World Health Assembly held on May 31, 2017. A guiding principle is that the path toward measles and rubella eradication should serve to strengthen primary health care, promote universal health coverage, and be a pathfinder for new vision and strategy for immunization over the next decade as laid out in the Immunization Agenda 2030. Specifically, this report: 1) highlights the importance of measles and rubella as global health priorities; 2) reviews the current global measles and rubella situation; 3) summarizes prior assessments of the feasibility of measles and rubella eradication; 4) assesses the progress and challenges in achieving regional measles and rubella elimination; 5) assesses additional considerations for measles and rubella eradication, including the results of modelling and economic analyses; 6) assesses the implications of establishing a measles and rubella eradication goal and the process for setting an eradication target date; 7) proposes a framework for determining preconditions for setting a target date for measles and rubella eradication and how these preconditions should be understood and used; and 8) concludes with recommendations endorsed by SAGE.

Socioeconomic deprivation is inversely associated with measles incidence: a longitudinal small-area analysis, Germany, 2001 to 2017

BackgroundAlthough measles is endemic throughout the World Health Organization European Region, few studies have analysed socioeconomic inequalities and spatiotemporal variations in the disease's incidence.AimTo study the association between socioeconomic deprivation and measles incidence in Germany, while considering relevant demographic, spatial and temporal factors.MethodsWe conducted a longitudinal small-area analysis using nationally representative linked data in 401 districts (2001-2017). We used spatiotemporal Bayesian regression models to assess the potential effect of area deprivation on measles incidence, adjusted for demographic and geographical factors, as well as spatial and temporal effects. We estimated risk ratios (RR) for deprivation quintiles (Q1-Q5), and district-specific adjusted relative risks (ARR) to assess the area-level risk profile of measles in Germany.ResultsThe risk of measles incidence in areas with lowest deprivation quintile (Q1) was 1.58 times higher (95% credible interval (CrI): 1.32-2.00) than in those with highest deprivation (Q5). Areas with medium-low (Q2), medium (Q3) and medium-high deprivation (Q4) had higher adjusted risks of measles relative to areas with highest deprivation (Q5) (RR: 1.23, 95%CrI: 0.99-1.51; 1.05, 95%CrI: 0.87-1.26 and 1.23, 95%CrI: 1.05-1.43, respectively). We identified 54 districts at medium-high risk for measles (ARR > 2) in Germany, of which 22 were at high risk (ARR > 3).ConclusionSocioeconomic deprivation in Germany, one of Europe's most populated countries, is inversely associated with measles incidence. This association persists after demographic and spatiotemporal factors are considered. The social, spatial and temporal patterns of elevated risk require targeted public health action and policy to address the complexity underlying measles epidemiology.

The Changing Global Epidemiology of Measles, 2013-2018

BACKGROUND

Measles incidence and mortality rates have significantly decreased since vaccine introduction. Despite this progress, however, there has been a global resurgence of measles. To understand the current global epidemiology, we analyzed measles surveillance data.

METHODS

We analyzed data on measles cases from 2013-2018 reported to the World Health Organization. Univariate analysis was undertaken based on age, vaccination history, onset year, World Health Organization region, and World Bank income status for the country where the case was reported, and a surrogate indicator of the historical strength of the country's immunization program. Annual incidence and a 2013-2018 mean country incidence per million were calculated.

RESULTS

From 2013 through 2018, there were 899 800 reported measles cases, of which 57% occurred unvaccinated or undervaccinated persons, with an unknown vaccination history in another 30%. Lower-middle-income countries accounted for 66% of cases, 23% occurred in persons ≥15 years of age. In countries with stronger historical vaccination programs and higher country income, case patients had higher median ages.

CONCLUSIONS

Although most measles case patients are <15 years of age, an age shift is seen in countries with a higher income or a stronger historical vaccination program. Countries must strengthen immunization programs to achieve high vaccination coverage; some must undertake strategies to reach persons ≥15 years of age and close immunity gaps.

Measles dynamics on network models with optimal control strategies

To investigate the influences of heterogeneity and waning immunity on measles transmission, we formulate a network model with periodic transmission rate, and theoretically examine the threshold dynamics. We numerically find that the waning of immunity can lead to an increase in the basic reproduction number R 0 and the density of infected individuals. Moreover, there exists a critical level for average degree above which R 0 increases quicker in the scale-free network than in the random network. To design the effective control strategies for the subpopulations with different activities, we examine the optimal control problem of the heterogeneous model. Numerical studies suggest us no matter what the network is, we should implement control measures as soon as possible once the outbreak takes off, and particularly, the subpopulation with high connectivity should require high intensity of interventions. However, with delayed initiation of controls, relatively strong control measures should be given to groups with medium degrees. Furthermore, the allocation of costs (or resources) should coincide with their contact patterns.

The top 1%: quantifying the unequal distribution of malaria in Brazil

Background

As malaria endemic countries strive towards elimination, intensified spatial heterogeneities of local transmission could undermine the effectiveness of traditional intervention policy.

Methods

The dynamic nature of large-scale and long-term malaria heterogeneity across Brazilian Amazon basin were explored by (1) exploratory analysis of Brazil’s rich clinical malaria reporting database from 2004 to 2018, and (2) adapting Gini coefficient to study the distribution of malaria cases in the region.

Results

As transmission declined, heterogeneity increased with cases clustering into smaller subpopulations across the territory. In 2004, the 1% of health units with the greatest number of cases accounted for 46% of all reported Plasmodium vivax cases, whereas in 2018 52% of P. vivax cases occurred in the top 1% of health units. Plasmodium falciparum had lower levels of transmission than P. vivax, and also had greater levels of heterogeneity with 75% of cases occurring in the top 1% of health units. Age and gender stratification of cases revealed peri-domestic and occupational exposure settings that remained relatively stable.

Conclusion

The pathway to decreasing incidence is characterized by higher proportions of cases in males, in adults, due to importation, and caused by P. vivax. Characterization of spatio-temporal heterogeneity and risk groups can aid stratification for improved malaria control towards elimination with increased heterogeneity potentially allowing for more efficient and cost-effective targeting. Although distinct epidemiological phenomena were clearly observed as malaria transmission declines, the authors argue that there is no canonical path to malaria elimination and a more targeted and dynamic surveillance will be needed if Brazil decides to adopt the elimination target.

Vaccination strategies for measles control and elimination: time to strengthen local initiatives

BACKGROUND

Through a combination of strong routine immunization (RI), strategic supplemental immunization activities (SIA) and robust surveillance, numerous countries have been able to approach or achieve measles elimination. The fragility of these achievements has been shown, however, by the resurgence of measles since 2016. We describe trends in routine measles vaccine coverage at national and district level, SIA performance and demographic changes in the three regions with the highest measles burden.

FINDINGS

WHO-UNICEF estimates of immunization coverage show that global coverage of the first dose of measles vaccine has stabilized at 85% from 2015 to 19. In 2000, 17 countries in the WHO African and Eastern Mediterranean regions had measles vaccine coverage below 50%, and although all increased coverage by 2019, at a median of 60%, it remained far below levels needed for elimination. Geospatial estimates show many low coverage districts across Africa and much of the Eastern Mediterranean and southeast Asian regions. A large proportion of children unvaccinated for MCV live in conflict-affected areas with remote rural areas and some urban areas also at risk. Countries with low RI coverage use SIAs frequently, yet the ideal timing and target age range for SIAs vary within countries, and the impact of SIAs has often been mitigated by delays or disruptions. SIAs have not been sufficient to achieve or sustain measles elimination in the countries with weakest routine systems. Demographic changes also affect measles transmission, and their variation between and within countries should be incorporated into strategic planning.

CONCLUSIONS

Rebuilding services after the COVID-19 pandemic provides a need and an opportunity to increase community engagement in planning and monitoring services. A broader suite of interventions is needed beyond SIAs. Improved methods for tracking coverage at the individual and community level are needed together with enhanced surveillance. Decision-making needs to be decentralized to develop locally-driven, sustainable strategies for measles control and elimination.

Elevated expansion of follicular helper T cells in peripheral blood from children with acute measles infection

BACKGROUND

Measles outbreaks have threatened the global elimination and eradication of measles in recent years. Measles virus (MeV)-specific antibodies are successful in clearing MeV infection. Follicular helper T (Tfh) cells play a crucial role in promoting antibody production. This study investigated the potential role of Tfh cells in peripheral blood mononuclear cells (PBMCs) from children with acute MeV infection.

RESULTS

The frequencies of CXCR5⁺CD4⁺ Tfh, ICOS^high Tfh, and PD-1^high Tfh cells in PBMCs and levels of IL-6 and IL-21 in plasma were significantly elevated in patients with acute MeV infection. Moreover, a positive correlation was discovered among the frequency of ICOS^high Tfh cells, plasma levels of IL-21 and optical density (OD) values of MeV-specific IgM antibodies in the patients with acute MeV infection. However, elevated plasma MeV-specific NAb titres were not associated with the frequency of Tfh, ICOS^high Tfh, or PD-1^high Tfh cells in the patients with acute MeV infection.

CONCLUSION

These results suggest that an elevated Tfh cell frequency and associated molecules possibly play a key role in children with acute MeV infection, which contributes to the prevention and treatment of MeV infection in children.

Predicting re-emergence times of dengue epidemics at low reproductive numbers: DENV1 in Rio de Janeiro, 1986-1990

Predicting arbovirus re-emergence remains challenging in regions with limited off-season transmission and intermittent epidemics. Current mathematical models treat the depletion and replenishment of susceptible (non-immune) hosts as the principal drivers of re-emergence, based on established understanding of highly transmissible childhood diseases with frequent epidemics. We extend an analytical approach to determine the number of ‘skip’ years preceding re-emergence for diseases with continuous seasonal transmission, population growth and under-reporting. Re-emergence times are shown to be highly sensitive to small changes in low R₀ (secondary cases produced from a primary infection in a fully susceptible population). We then fit a stochastic Susceptible–Infected–Recovered (SIR) model to observed case data for the emergence of dengue serotype DENV1 in Rio de Janeiro. This aggregated city-level model substantially over-estimates observed re-emergence times either in terms of skips or outbreak probability under forward simulation. The inability of susceptible depletion and replenishment to explain re-emergence under ‘well-mixed’ conditions at a city-wide scale demonstrates a key limitation of SIR aggregated models, including those applied to other arboviruses. The predictive uncertainty and high skip sensitivity to epidemiological parameters suggest a need to investigate the relevant spatial scales of susceptible depletion and the scaling of microscale transmission dynamics to formulate simpler models that apply at coarse resolutions.

Measles immunity gaps in an era of high vaccination coverage: A serology study from Taiwan

BACKGROUND

Routine vaccination for children drastically reduces measles cases. Nonetheless, the global resurgence of measles since 2018 highlights the need for evaluating vaccine-induced immunity in an era of high vaccination coverage, especially in international travelers. This study aims to identify high-risk persons via analyzing the impact of age and different vaccination schedules on seroprevalence of measles in a country with high vaccination coverage, attempting to provide suggestions regarding pre-travel measles vaccination in highly immunized countries.

METHOD

We retrospectively collected serological results of measles from Taiwanese travelers during 2008-2017 and middle-aged subjects from community during 2007-2009. Participants were classified by age groups and cohort based on the national immunization program: cohort I (pre-mass vaccination), cohort II (suboptimal measles vaccination), and cohort III (2-dose MMR in childhood). The effects of age group on seropositivity was shown by odds ratio (OR) with 95% confidence interval (CI) in a logistic regression model.

RESULTS

The overall measles seroprevalence was 74.5% (N = 1096, mean age = 31.7 ± 12.3 years), with adolescents having the lowest seropositivity (65.9%) and participants ≥50 years having the highest (89.4%). Seropositivity was significantly higher in cohort I (pre-mass vaccination) compared with the other 2 cohorts (P < 0.0001). The effect of aging on seropositivity was only significant in cohort II (OR = 1.84, 95% CI = 1.13-2.99, P = 0.014 for 30-39 years vs. 20-29 years).

CONCLUSIONS

Waning immunity to measles in adolescents and young adults is a dominant issue in highly vaccinated cohorts. Enhancing pre-travel vaccination against measles can effectively fill the immunity gaps in highly immunized countries.

Dynamical footprints enable detection of disease emergence

Developing methods for anticipating the emergence or reemergence of infectious diseases is both important and timely; however, traditional model-based approaches are stymied by uncertainty surrounding the underlying drivers. Here, we demonstrate an operational, mechanism-agnostic detection algorithm for disease (re-)emergence based on early warning signals (EWSs) derived from the theory of critical slowing down. Specifically, we used computer simulations to train a supervised learning algorithm to detect the dynamical footprints of (re-)emergence present in epidemiological data. Our algorithm was then challenged to forecast the slowly manifesting, spatially replicated reemergence of mumps in England in the mid-2000s and pertussis post-1980 in the United States. Our method successfully anticipated mumps reemergence 4 years in advance, during which time mitigation efforts could have been implemented. From 1980 onwards, our model identified resurgent states with increasing accuracy, leading to reliable classification starting in 1992. Additionally, we successfully applied the detection algorithm to 2 vector-transmitted case studies, namely, outbreaks of dengue serotypes in Puerto Rico and a rapidly unfolding outbreak of plague in 2017 in Madagascar. Taken together, these findings illustrate the power of theoretically informed machine learning techniques to develop early warning systems for the (re-)emergence of infectious diseases.

A competing-risks model explains hierarchical spatial coupling of measles epidemics en route to national elimination

Apart from its global health importance, measles is a paradigm for the low-dimensional mechanistic understanding of local nonlinear population interactions. A central question for spatio-temporal dynamics is the relative roles of hierarchical spread from large cities to small towns and metapopulation transmission among local small population clusters in measles persistence. Quantifying this balance is critical to planning the regional elimination and global eradication of measles. Yet, current gravity models do not allow a formal comparison of hierarchical versus metapopulation spread. We address this gap with a competing-risks framework, capturing the relative importance of competing sources of reintroductions of infection. We apply the method to the uniquely spatio-temporally detailed urban incidence dataset for measles in England and Wales, from 1944 to the infection's vaccine-induced nadir in the 1990s. We find that despite the regional influence of a few large cities (for example, London and Liverpool), metapopulation aggregation in neighbouring towns and cities played an important role in driving national dynamics in the prevaccination era. As vaccination levels increased in the 1970s and 1980s, the signature of spatially predictable spread diminished: increasingly, infection was introduced from unidentifiable random sources possibly outside regional metapopulations. The resulting erratic dynamics highlight the challenges of identifying shifting sources of infection and characterizing patterns of incidence in times of high vaccination coverage. More broadly, the underlying incidence and demographic data, accompanying this paper, will also provide an important resource for exploring nonlinear spatiotemporal population dynamics.

Resurgence of measles in the United States: how did we get here?

PURPOSE OF REVIEW

In September 2019, the United States was at risk of losing measles elimination status due to several large-scale outbreaks resulting in more than 1200 confirmed cases across 31 states. This resurgence caps approximately 10 years of increasing incidence, marked by a highly publicized outbreak in 2015 associated with Disneyland when an infected traveler from the Philippines unknowingly spread the virus to susceptible park visitors and the recently ended large outbreak in undervaccinated Orthodox Jewish communities in New York City and Rockland counties. This review highlights current literature elucidating factors associated with current trends in measles epidemiology in the United States, the public health implications of current measles outbreaks and a path forward for addressing challenges contributing to the resurgence of measles in the United States and globally.

RECENT FINDINGS AND SUMMARY

As the most highly transmissible vaccine preventable disease, measles is especially sensitive to changes in herd immunity, the impact of vaccine refusal and globalization. Results highlight the confluence of these factors in current outbreaks, provide tools to predict outbreak risk, demonstrate the growing impact of misinformation and evaluate the impact of policy approaches for outbreak control and prevention.

Using models to shape measles control and elimination strategies in low- and middle-income countries: A review of recent applications

After many decades of vaccination, measles epidemiology varies greatly between and within countries. National immunization programs are therefore encouraged to conduct regular situation analyses and to leverage models to adapt interventions to local needs. Here, we review applications of models to develop locally tailored interventions to support control and elimination efforts. In general, statistical and semi-mechanistic transmission models can be used to synthesize information from vaccination coverage, measles incidence, demographic, and/or serological data, offering a means to estimate the spatial and age-specific distribution of measles susceptibility. These estimates complete the picture provided by vaccination coverage alone, by accounting for natural immunity. Dynamic transmission models can then be used to evaluate the relative impact of candidate interventions for measles control and elimination and the expected future epidemiology. In most countries, models predict substantial numbers of susceptible individuals outside the age range of routine vaccination, which affects outbreak risk and necessitates additional intervention to achieve elimination. More effective use of models to inform both vaccination program planning and evaluation requires the development of training to enhance broader understanding of models and where feasible, building capacity for modelling in-country, pipelines for rapid evaluation of model predictions using surveillance data, and clear protocols for incorporating model results into decision-making.

Multi-sectorial research is paramount for preventing and controlling emerging infectious diseases

The social, economic and political consequences of emerging infectious disease (EID) may escape the sphere in which they first arise. In recent years, many EIDs have revealed the close links between human, animal and plant health, highlighting the need for multi-scale, multisectorial EID management. Human beings play a dual role in EID because they can promote their development through numerous human-environment interfaces and expanding international trade. On the other hand, their ability to analyze, interpret and act on the determinants of EID allows them to access the expertise necessary to control these EIDs. This expertise must be constantly adapted to remain relevant as the EID evolves, particularly in its virulence or transmission channels. Flexibility should become an inherent part of the expertise-based decision-making process even if it means going backwards. A certain degree of transparency and feedback to citizens is necessary for the acceptability of political decisions basing on expertise. A key step in the management of EID is the appropriate management of the early signal of infectious emergence. This step combines multidisciplinary skills allowing access to the best pathway for containing EID by implementing early countermeasures adapted to the situation. New digital technologies could significantly improve this early detection phase. Finally, experts have a fundamental role to play because they are located at the interface between operational actors and decision-makers, which allows multidirectional feedback, ideally in real time, between professional actors and decision makers. To combat current and future EIDs, expertise should be based on a multi-sectorial approach, promotion of collegiality and continuously adaptation to the evolving nature of EIDs.