Rapid diagnostic tests to address challenges for global measles surveillance

The Global Measles and Rubella Laboratory Network Supports High-Quality Surveillance

With 762 laboratories, the Global Measles and Rubella Laboratory Network (GMRLN) is the largest laboratory network coordinated by the World Health Organization (WHO). Like the Global Polio Laboratory Network, the GMRLN has multiple tiers, including global specialized laboratories, regional reference laboratories, national laboratories, and, in some countries, subnational laboratories. Regional networks are supervised by regional laboratory coordinators reporting to a global coordinator at WHO headquarters. Laboratories in the GMRLN have strong links to national disease control and vaccination programs. The GMRLN's goal is to support member states in obtaining timely, complete, and reliable laboratory-based surveillance data for measles and rubella as part of the strategy for achieving measles and rubella elimination. Surveillance data are reported to the national program and are included in annual reports on the status of measles and rubella elimination to national verification committees for review by regional verification commissions. Quality within the GMRLN is ensured by monitoring performance through external quality assurance programs, confirmatory and quality control testing, accreditation, and coordination of corrective action and training where needed. The overall performance of the laboratories has remained high over the years despite many challenges, particularly the COVID-19 pandemic. The GMRLN is well-positioned to support high-quality laboratory-based surveillance for measles and rubella and to transition to supporting laboratory testing for other pathogens, including vaccine-preventable diseases.

Tracking Measles and Rubella Elimination Progress-World Health Organization African Region, 2022-2023

Measles or rubella elimination is verified when endemic transmission of the corresponding virus has been absent for over 36 months in a defined area, in the presence of a well-performing surveillance system. This report updates the progress by 47 countries in the WHO African Region towards the goal of attaining verification of measles and rubella elimination in at least 80% of the countries of the region by 2030. We reviewed the WHO-UNICEF vaccination coverage estimates for the first and second doses of measles- and measles-rubella-containing vaccines, as well as the available coverage data for measles supplementary immunization activities, during 2022-2023. We also reviewed the measles-surveillance performance and analyzed the epidemiological trends of measles and rubella as reported in the case-based surveillance database. The WHO-UNICEF estimates of first measles vaccine dose (MCV1) and second measles vaccine dose (MCV2) coverage for the African Region for 2022 were 69% and 45%, respectively. Rubella-containing vaccines have been introduced in the routine immunization program in 32 of 47 (68%) countries as of the end of 2022, with no introductions during 2023. In 2022 and 2023, a total of 144,767,764 children were vaccinated in the region with measles or MR vaccines in 24 countries through 32 mass vaccination campaigns. The administrative coverage target of 95% was reached in only 15 (49%) of the 32 vaccination campaigns. In 2023, a total of 125,957 suspected cases of measles were reported through the case-based surveillance system, and 73,625 cases (58%) were confirmed to be measles, either by laboratory testing, by epidemiological linkage, or based on clinical compatibility. A total of 4805 confirmed rubella cases were reported, though this total represents substantial under-ascertainment. The regional incidence of measles was 60.3 cases per million population. Twenty-six countries (55%) met the targets for the two principal surveillance system performance-monitoring indicators. No country in the region has attained the verification of measles or rubella elimination as of the end of 2023. Addressing systemic problems with routine immunization and using tailored approaches to reach unvaccinated children can contribute to progress towards measles and rubella elimination. In addition, periodic and timely high-quality preventive SIAs remain a critical programmatic strategy to reach unvaccinated children.

What's going on with measles?

Measles is a highly transmissible systemic viral infection associated with substantial mortality primarily due to secondary infections. Measles induces lifelong immunity to reinfection but loss of immunity to other pathogens. An attenuated live virus vaccine is highly effective, but lapses in delivery have resulted in increasing cases worldwide. Although the primary cause of failure to control measles is failure to vaccinate, waning vaccine-induced immunity and the possible emergence of more virulent virus strains may also contribute.

Use of Measles and Rubella Rapid Diagnostic Tests to Improve Case Detection and Targeting of Vaccinations

Efforts to control and eliminate measles and rubella are aided by high-quality surveillance data-supported by laboratory confirmation-to guide decision-making on routine immunization strategies and locations for conducting preventive supplementary immunization activities (SIAs) and outbreak response. Important developments in rapid diagnostic tests (RDTs) for measles and rubella present new opportunities for the global measles and rubella surveillance program to greatly improve the ability to rapidly detect and respond to outbreaks. Here, we review the status of RDTs for measles and rubella Immunoglobulin M (IgM) testing, as well as ongoing questions and challenges regarding the operational use and deployment of RDTs as part of global measles and rubella surveillance. Efforts to develop IgM RDTs that can be produced at scale are underway. Once validated RDTs are available, clear information on the benefits, challenges, and costs of their implementation will be critical for shaping deployment guidance and informing country plans for sustainably deploying such tests. The wide availability of RDTs could provide new programmatic options for measles and rubella elimination efforts, potentially enabling improvements and flexibility for testing, surveillance, and vaccination.

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.

The Problem with Delaying Measles Elimination

Measles is a highly infectious disease leading to high morbidity and mortality impacting people's lives and economies across the globe. The measles vaccine saves more lives than any other vaccine in the Essential Programme of Immunization and is also the most cost-effective vaccine, with an extremely high return on investment. This makes achieving measles elimination through vaccination a key child health intervention, particularly in low-income countries, where the overwhelming majority of measles deaths continue to occur. All countries and regions of the world have committed to achieving measles elimination, yet many have faced challenges securing political commitment at national and global levels and predictable, timely, and flexible support from global donors, and experienced setbacks during the COVID-19 pandemic. This has happened against a backdrop of stagnant measles vaccination coverage and declining enthusiasm for vertical programmes, culminating in a World Health Organization Strategic Advisory Group of Experts (WHO SAGE) review of the feasibility of measles eradication in 2019. Sustaining the elimination of measles long term is extremely difficult, and some countries have lost or nearly lost their measles elimination status in the face of ongoing importation of cases from neighbouring or closely connected countries in which elimination had been delayed. Thus, a widening equity gap in measles immunisation coverage creates challenges for all countries, not just those facing the greatest burden of measles morbidity and mortality. Delaying elimination of measles in some countries makes it cumulatively harder for all countries to succeed for three principal reasons: increased inequity in measles immunisation coverage makes outbreaks more likely to happen and to be larger; political will is very difficult to sustain; and immunity may wane to a point that transmission is re-established. New strategies are needed to support countries and regions in their vision for a world without measles, including ways to galvanise domestic, regional and global resources and ignite the political will that is essential to make the vision a reality.

Measles and Rubella Diagnostic and Classification Challenges in Near- and Post-Elimination Countries

Measles and rubella are vaccine-preventable viral diseases and can be prevented by safe, highly effective vaccination with measles- and rubella-containing vaccines. Given the myriad causes of febrile exanthems, laboratory surveillance for both measles and rubella is important to document the incidence of these diseases and to track the progress and maintenance of elimination in near- and post-elimination settings. Diagnostic challenges can hinder effective surveillance and classification challenges can hinder efforts to demonstrate achievement or maintenance of elimination. In this report, we review diagnostic and classification challenges for measles and rubella in near- and post-elimination settings.

Modeling the transmission mitigation impact of testing for infectious diseases

A fundamental question of any program focused on the testing and timely diagnosis of a communicable disease is its effectiveness in reducing transmission. Here, we introduce testing effectiveness (TE)-the fraction by which testing and post-diagnosis isolation reduce transmission at the population scale-and a model that incorporates test specifications and usage, within-host pathogen dynamics, and human behaviors to estimate TE. Using TE to guide recommendations, we show that today's rapid diagnostics should be used immediately upon symptom onset to control influenza A and respiratory syncytial virus but delayed by up to two days to control omicron-era severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Furthermore, while rapid tests are superior to reverse transcription quantitative polymerase chain reaction (RT-qPCR) to control founder-strain SARS-CoV-2, omicron-era changes in viral kinetics and rapid test sensitivity cause a reversal, with higher TE for RT-qPCR despite longer turnaround times. Last, we illustrate the model's flexibility by quantifying trade-offs in the use of post-diagnosis testing to shorten isolation times.

A measles IgM rapid diagnostic test to address challenges with national measles surveillance and response in Malaysia

INTRODUCTION

A lateral flow rapid diagnostic test (RDT) enables detection of measles specific immunoglobulin M (IgM) antibody in serum, capillary blood, and oral fluid with accuracy consistent with enzyme immunoassay (EIA). The objectives of the study were: 1) to assess measles RDT inter-reader agreement between two clinic staff; 2) to assess the sensitivity and specificity of the measles RDT relative to standard surveillance testing in a low transmission setting; 3) to evaluate the knowledge, attitudes, and practices of staff in clinics using the RDT; and 4) to assess the impact of RDT testing on the measles public health response in Malaysia.

MATERIALS AND METHODS

The clinic-based prospective evaluation included all suspected measles cases captured by routine measles surveillance at 34 purposely selected clinics in 15 health districts in Malaysia between September 2019 and June 2020, following day-long regional trainings on RDT use. Following informed consent, four specimens were collected from each suspected case, including those routinely collected for standard surveillance [serum for EIA and throat swabs for quantitative reverse transcriptase polymerase chain reaction (RT-qPCR)] together with capillary blood and oral fluid tested with RDTs during the study. RDT impact was evaluated by comparing the rapidity of measles public health response between the pre-RDT implementation (December 2018 to August 2019) and RDT implementation periods (September 2019 to June 2020). To assess knowledge, attitudes, and practices of RDT use, staff involved in the public health management of measles at the selected sites were surveyed.

RESULTS

Among the 436 suspect cases, agreement of direct visual readings of measles RDT devices between two health clinic staff was 99% for capillary blood (k = 0.94) and 97% for oral fluid (k = 0.90) specimens. Of the total, 45 (10%) were positive by measles IgM EIA (n = 44, including five also positive by RT-qPCR) or RT-qPCR only (n = 1), and 38 were positive by RDT (using either capillary blood or oral fluid). Using measles IgM EIA or RT-qPCR as reference, RDT sensitivity using capillary blood was 43% (95% CI: 30%-58%) and specificity was 98% (95% CI: 96%-99%); using oral fluid, sensitivity (26%, 95% CI: 15%-40%) and specificity (97%, 95% CI: 94%-98%) were lower. Nine months after training, RDT knowledge was high among staff involved with the public health management of measles (average quiz score of 80%) and was highest among those who received formal training (88%), followed by those trained during supervisory visits (83%). During the RDT implementation period, the number of days from case confirmation until initiation of public response decreased by about 5 days.

CONCLUSION

The measles IgM RDT shows >95% inter-reader agreement, high retention of RDT knowledge, and a more rapid public health response. However, despite ≥95% RDT specificity using capillary blood or oral fluid, RDT sensitivity was <45%. Higher-powered studies using highly specific IgM assays and systematic RT-qPCR for case confirmation are needed to establish the role of RDT in measles elimination settings.

Rapid Detection of Measles Virus Using Reverse Transcriptase/Recombinase Polymerase Amplification Coupled with CRISPR/Cas12a and a Lateral Flow Detection: A Proof-of-Concept Study

The measles virus is highly contagious, and efforts to simplify its diagnosis are essential. A reverse transcriptase/recombinase polymerase amplification assay coupled with CRISPR/Cas12a and an immunochromatographic lateral flow detection (RT-RPA-CRISPR-LFD) was developed for the simple visual detection of measles virus. The assay was performed in less than 1 h at an optimal temperature of 42 °C. The detection limit of the assay was 31 copies of an RNA standard in the reaction tube. The diagnostic performances were evaluated on a panel of 27 measles virus RT-PCR-positive samples alongside 29 measles virus negative saliva samples. The sensitivity and specificity were 96% (95% CI, 81-99%) and 100% (95% CI, 88-100%), respectively, corresponding to an accuracy of 98% (95% CI, 94-100%; p < 0.0001). This method will open new perspectives in the development of the point-of-care testing diagnosis of measles.

Dimeric immunoglobulin A as a novel diagnostic marker of measles infection

IMPORTANCE

The world is facing a measles resurgence, and improved diagnostic tests for measles infection are an urgent World Health Organization research priority. Detection of measles-specific immunoglobulin M (IgM) as a standard diagnostic test has low positive predictive value in elimination settings, and there is a need for new biomarkers of measles infection to enable enhanced surveillance and response to outbreaks. We demonstrate the detection of measles-specific dimeric immunoglobulin A (dIgA) in patients with confirmed measles infections using a new indirect enzyme-linked immunosorbent assay protocol that selects for the dIgA fraction from total IgA in the blood. The magnitude of measles-specific dIgA responses showed a low correlation with IgM responses, and our results highlight the potential of dIgA for further development as an alternative and/or complementary biomarker to IgM for serological diagnosis of measles infection.

Use of a rapid digital microfluidics-powered immunoassay for assessing measles and rubella infection and immunity in outbreak settings in the Democratic Republic of the Congo

The Democratic Republic of the Congo (DRC) has a high measles incidence despite elimination efforts and has yet to introduce rubella vaccine. We evaluated the performance of a prototype rapid digital microfluidics powered (DMF) enzyme-linked immunoassay (ELISA) assessing measles and rubella infection, by testing for immunoglobulin M (IgM), and immunity from natural infection or vaccine, by testing immunoglobulin G (IgG), in outbreak settings. Field evaluations were conducted during September 2017, in Kinshasa province, DRC. Blood specimens were collected during an outbreak investigation of suspected measles cases and tested for measles and rubella IgM and IgG using the DMF-ELISA in the field. Simultaneously, a household serosurvey for measles and rubella IgG was conducted in a recently confirmed measles outbreak area. DMF-ELISA results were compared with reference ELISA results tested at DRC's National Public Health Laboratory and the US Centers for Disease Control and Prevention. Of 157 suspected measles cases, rubella IgM was detected in 54% while measles IgM was detected in 13%. Measles IgG-positive cases were higher among vaccinated persons (87%) than unvaccinated persons (72%). In the recent measles outbreak area, measles IgG seroprevalence was 93% overall, while rubella seroprevalence was lower for children (77%) than women (98%). Compared with reference ELISA, DMF-ELISA sensitivity and specificity were 82% and 78% for measles IgG; 88% and 89% for measles IgM; 85% and 85% for rubella IgG; and 81% and 83% for rubella IgM, respectively. Rubella infection was detected in more than half of persons meeting the suspected measles case definition during a presumed measles outbreak, suggesting substantial unrecognized rubella incidence, and highlighting the need for rubella vaccine introduction into the national schedule. The performance of the DMF-ELISA suggested that this technology can be used to develop rapid diagnostic tests for measles and rubella.

Experiences of sharing results of community based serosurvey with participants in a district of Maharashtra, India

A growing number of organisations, including medical associations, recommend that research subjects should be given the option of being informed about the general outcome and results of the study. We recently completed a study involving nine serosurveys from 2018 to 2020 in five districts of India among three age groups (children 9 months to < 5 years; 5 to < 15 years of age, and women 15 to < 50 years of age before and after the measles and rubella (MR) vaccination campaigns). In Palghar district of Maharashtra all individuals in 30 selected clusters were enumerated, and 13 individuals per age group were randomly sampled. We established the procedures to return the results to the respondents for each stage of the survey. Of the 1,166 individuals selected for the measles and rubella serosurvey, 971 (83%) agreed to participate and were enrolled. Participants were informed that they will only be contacted if they test seronegative for measles and/or rubella antibodies. Overall, 140 individuals enrolled in the survey tested seronegative for IgG antibodies to measles and/or rubella viruses; were provided the reports and informed to seek medical advice. Upon follow up by phone, 10% (14) of the 140 participants reported to have been vaccinated. In this paper we discuss the procedures, experiences and considerations in returning results to participants in a community-based measles and rubella serosurvey. Although the lessons learned are specific to post measles-rubella vaccine campaign serosurvey in India, they might be helpful to those contemplating sharing results to participants of large scale survey settings.

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.

The impact of the COVID-19 pandemic on measles surveillance in the World Health Organisation African Region, 2020

Introduction

following the declaration of the COVID-19 pandemic, many countries imposed restrictions on public gatherings, health workers were repurposed for COVID-19 response, and public demand for preventive health services declined due to fear of getting COVID-19 in health care settings. These factors led to the disruption in health service delivery, including childhood immunization, in the first months of the pandemic. Measles surveillance supported with laboratory confirmation, is implemented in the African Region as part of the strategies towards attaining measles elimination. World Health Organisation developed guidelines to assist countries to continue to safely provide essential health services including immunization and the surveillance of vaccine preventable diseases during the pandemic.

Methods

we analysed the measles case-based surveillance and laboratory databases for the years 2014 to 2020, to determine the impact of the COVID-19 pandemic on measles surveillance, comparing the performance in 2020 against the preceding years.

Results

the weekly reporting of suspected measles cases declined starting in April 2020. Twelve countries had more than 50% decline in both the number of reported cases as well as in the number of specimens collected in 2020, as compared to the mean for the years 2014-2018. In 2020, only 30% of the specimens from suspected measles cases arrived at the national laboratory within 3 days of collection. At Regional level, 86% of the districts reported suspected measles cases in 2020, while the non-measles febrile rash illness rate was 2.1 per 100,000 population, which was the lowest rate documented since 2014. Only 11 countries met the targets for the two principal surveillance performance indicators in 2020 as compared to an average of 21 countries in the years 2014-2019.

Conclusion

the overall quality of measles surveillance has declined during the COVID pandemic in many countries. Countries should implement immediate and proactive measures to revitalise active surveillance for measles and monitor the quality of surveillance. We recommend that countries consider implementing specimen collection and testing methods that can facilitate timely confirmation of suspected measles cases in remote communities and areas with transportation challenges.

An efficient molecular approach to distinguish chains of measles virus transmission in the elimination phase

Measles viruses continue to spread globally, despite the availability of a safe and effective vaccine. Molecular surveillance of measles virus has become an essential tool to demonstrate whether cascades of infections in a certain region or country are the result of endemic spread or the repeatedly introduction of the virus in contained outbreaks. Currently, molecular surveillance of measles viruses worldwide is mainly based on 450 nucleotides of the C-terminal region of the nucleoprotein (N450). However, as a result of the disappearance of particular measles virus clades over the past decades, this gene segment does not provide sufficient resolution anymore to answer these questions. To increase the molecular resolution, sequence data were collected from three regions of the measles virus genome, the partial non-coding region between the M and F gene (M-F NCR_4465-4754), partial H gene (H_8022-8621) and the partial L gene (L_10724-11438) for measles viruses detected in 2018 and 2019 in the Netherlands. Analysis of obtained sequence data indicated that sequencing of these three regions resulted in an increase in molecular resolution for measles virus genotype B3 and D8 viruses, two of the four global genotypes currently predominant in the European region. Furthermore, this improved resolution was sufficient to support an epidemiology characterized by repeat introduction of measles virus rather than endemic virus spread. In conclusion, sequencing of the M-F NCR_4465-4754, H_8022-8621 and L_10724-11438 regions of the measles virus is an efficient and useful approach for molecular surveillance of measles viruses.

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.