What Is the Evidence to Support a Correlate of Protection for Measles? A Systematic Review

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.

Serosurveillance for Measles and Rubella

Measles and rubella remain global health threats, despite the availability of safe and effective vaccines. Estimates of population immunity are crucial for achieving elimination goals and assessing the impact of vaccination programs, yet conducting well-designed serosurveys can be challenging, especially in resource-limited settings. In this review, we provide a comprehensive assessment of 130 measles and rubella studies published from January 2014 to January 2024. Methodologies and design aspects of serosurveys varied greatly, including sample size, assay type, and population demographics. Most studies utilized enzyme immunoassays for IgG detection. Sample sizes showed diverse sampling methods but favored convenience sampling despite its limitations. Studies spanned 59 countries, predominantly including adults, and revealed disparities in seroprevalence across demographics, regions, and notably among migrants and women. Age-related declines in antibodies were observed, particularly among infants, and correlations between vaccination status and seropositivity varied. We conclude with an outlook on measles and rubella serosurveillance, emphasizing the need for proper survey design and the advantages of standardized, multiplex serology assays.

Age-specific prevalence of IgG against measles/rubella and the impact of routine and supplementary immunization activities: A multistage random cluster sampling study with mathematical modelling

BACKGROUND

Vietnam continues to have measles and rubella outbreaks following supplementary immunization activities (SIA) and routine immunization despite both having high reported coverage. To evaluate immunization activities, age-specific immunity against measles and rubella, and the number of averted Congenital Rubella Syndrome (CRS) cases, must be estimated.

METHODS

Dried blood spots were collected from 2091 randomly selected individuals aged 1-39 years. Measles and rubella virus-specific immunoglobulin G (IgG) were measured by enzyme immunoassay. Results were considered positive at ≥120 mIU/mL for measles and ≥10 IU/mL for rubella. The number of CRS cases averted by immunization since 2014 were estimated using mathematical modelling.

RESULTS

Overall IgG seroprevalence was 99.7% (95%CI: 99.2-99.9) for measles and 83.6% (95%CI: 79.3-87.1) for rubella. Rubella IgG seroprevalence was higher among age groups targeted in the SIA than in non-targeted young adults (95.4% [95%CI: 92.9-97.0] vs 72.4% [95%CI: 63.1-80.1]; P < 0.001). The estimated number of CRS cases averted in 2019 by immunization activities since 2014 ranged from 126 (95%CI: 0-460) to 883 (95%CI: 0-2271) depending on the assumed postvaccination reduction in the force of infection.

CONCLUSIONS

The results suggest the SIA was effective, while young adults born before 1998 who remain unprotected for rubella require further vaccination.

Measles Foci Reduction Neutralization Test (FRNT)

The plaque reduction neutralization test (PRNT) and the enzyme-linked immunosorbent assay (ELISA) are both widely used to assess immunity to infectious diseases such as measles, but they use two different measurement principles: ELISA measures the ability of antibodies to bind to virus components, while the PRNT detects the aptitude of antibodies to prevent the infection of a susceptible cell. As a result, detection of measles virus (MV) neutralizing antibodies is the gold standard for assessing immunity to measles. However, the assay is laborious and requires experience and excellent technical skills. In addition, the result is only available after several days. Therefore, the classical PRNT is not suitable for high-throughput testing. By using an immunocolorimetric assay (ICA) to detect MV-infected cells, the standard PRNT has been developed into a focus reduction neutralization test (FRNT). This assay is faster and has improved specificity. The FRNT described here is extremely useful when immunity to measles virus needs to be assessed in patients with a specific medical condition, such as immunocompromised individuals in whom presumed residual immunity needs to be assessed. The FRNT is not generally recommended for use with large numbers of specimens, such as in a seroprevalence study.

Population measles seroprevalence: Heterogeneity by birth-year cohort

Objective

This work sought to estimate population measles seroprevalence and heterogeneity in the antibody concentration distribution that could be explained by the birth-year cohort according to the opportunity of viral and vaccine exposure, applied to data from Medellín, Colombia.

Methods

Prevalence of IgG antibodies was analyzed for measles based on a population study with a random sample of 2098 individuals from 6 to 64 years of age. Finite mixture models were used to estimate global seroprevalence and that of three birth-year cohorts (I: born up to 1982; II: 1983-1994; III: born since 1995). Multiple linear regression permitted adjusting the concentration of antibodies by cohort, zone, and sex.

Results

Globally, seronegativity was 6.5% (95% CI 4.9- 8.6), seropositivity of 78.4% (95% CI 75.1-81.4), and equivocal of 15.1% (95% CI 12.5-18.1). Two components were found with skewed normal distribution, which reclassified those equivocal as seropositive. Differences were observed by cohort in the geometric mean of antibodies [Cohort I: 1704.6; II: 562.2; III: 802.1 milli-international units per milliliter (mIU/mL] and seronegativity (Cohort I: 4%; II:13.3%; III: 8.9%). Antibody concentration increased by 1.26 mIU/mL in residents in the rural area, while diminishing in individuals from cohort II (by 3.02 mIU/mL) and cohort III (by 2.14 mIU/mL).

Conclusion

The younger cohorts (II and III) had a lower antibody concentration (higher seronegativity), indicating the need to monitor periodically seroprevalence and an eventual reestablishment of the transmission in these groups with higher risk of infection.

Safety, Tolerability, and Immunogenicity of Measles and Rubella Vaccine Delivered with a High-Density Microarray Patch: Results from a Randomized, Partially Double-Blinded, Placebo-Controlled Phase I Clinical Trial

Microarray patches (MAPs) have the potential to be a safer, more acceptable, easier-to-use, and more cost-effective means for the administration of vaccines than injection by needle and syringe. Here, we report findings from a randomized, partially double-blinded, placebo-controlled Phase I trial using the Vaxxas high-density MAP (HD-MAP) to deliver a measles rubella (MR) vaccine. Healthy adults (N = 63, age 18-50 years) were randomly assigned 1:1:1:1 to four groups: uncoated (placebo) HD-MAPs, low-dose MR HD-MAPs (~3100 median cell-culture infectious dose [CCID50] measles, ~4300 CCID50 rubella); high-dose MR-HD-MAPs (~9300 CCID50 measles, ~12,900 CCID50 rubella); or a sub-cutaneous (SC) injection of an approved MR vaccine, MR-Vac (≥1000 CCID50 per virus). The MR vaccines were stable and remained viable on HD-MAPs when stored at 2-8 °C for at least 24 months. When MR HD-MAPs stored at 2-8 °C for 24 months were transferred to 40 °C for 3 days in a controlled temperature excursion, loss of potency was minimal, and MR HD-MAPs still met World Health Organisation (WHO) specifications. MR HD-MAP vaccination was safe and well-tolerated; any systemic or local adverse events (AEs) were mild or moderate. Similar levels of binding and neutralizing antibodies to measles and rubella were induced by low-dose and high-dose MR HD-MAPs and MR-Vac. The neutralizing antibody seroconversion rates on day 28 after vaccination for the low-dose HD-MAP, high-dose HD-MAP and MR-Vac groups were 37.5%, 18.8% and 35.7%, respectively, for measles, and 37.5%, 25.0% and 35.7%, respectively, for rubella. Most participants were seropositive for measles and rubella antibodies at baseline, which appeared to negatively impact the number of participants that seroconverted to vaccines delivered by either route. The data reported here suggest HD-MAPs could be a valuable means for delivering MR-vaccine to hard-to-reach populations and support further development. Clinical trial registry number: ACTRN12621000820808.

Seroprevalence and prevention of hepatitis B, measles and rubella among healthcare workers in Dili, Timor-Leste

Introduction

The World Health Organisation recommends that healthcare workers (HCWs) are immune to measles and rubella, and those at risk of exposure are offered the hepatitis B vaccine. No formal programme for occupational assessment and provision of vaccinations to HCWs currently exists in Timor-Leste.

Methods

A cross-sectional study was undertaken to determine the seroprevalence of hepatitis B, measles and rubella among HCWs in Dili, Timor-Leste. All patient-facing employees at three healthcare institutions during April-June 2021 were invited to participate. Epidemiological data were collected by interview-questionnaire and a serum sample was collected by phlebotomy and analysed at the National Health Laboratory. Participants were contacted to discuss their results. Relevant vaccines were offered to seronegative individuals and those with active hepatitis B infection were referred for further assessment and management in a hepatology clinic as per national guidelines.

Results

Three-hundred-and-twenty-four HCWs were included (representing 51.3% of all eligible HCWs working at the three participating institutions). Sixteen (4.9%; 95% CI: 2.8-7.9%) had active hepatitis B infection, 121 (37.3%; 95% CI: 32.1-42.9%) had evidence of previous (cleared) hepatitis B infection, 134 (41.4%; 95% CI: 35.9-46.9%) were hepatitis B seronegative, and 53 (16.4%; 95% CI: 12.5-20.8%) had been vaccinated. Two-hundred-and-sixty-seven (82.4%; 95% CI: 77.8-86.4%) and 306 (94.4%; 95% CI: 91.4-96.7%) individuals exhibited antibodies to measles and rubella, respectively.

Interpretation

There are significant immunity gaps and a high prevalence of hepatitis B infection among HCWs in Dili Municipality, Timor-Leste. Routine occupational assessment and targeted vaccination of this group would be beneficial and should include all types of HCWs. This study provided an opportunity to develop a programme for the occupational assessment and vaccination of HCWs and forms the template for a national guideline.

Funding

This work was supported by the Department of Foreign Affairs and Trade, Australian Government [Complex Grant Agreement Number 75889].

Comparison of measles IgG enzyme immunoassays (EIA) versus plaque reduction neutralization test (PRNT) for measuring measles serostatus: a systematic review of head-to-head analyses of measles IgG EIA and PRNT

BACKGROUND

As countries move towards or achieve measles elimination status, serosurveillance is an important public health tool. However, a major challenge of serosurveillance is finding a feasible, accurate, cost-effective, and high throughput assay to measure measles antibody concentrations and estimate susceptibility in a population. We conducted a systematic review to assess, characterize, and - to the extent possible - quantify the performance of measles IgG enzyme-linked assays (EIAs) compared to the gold standard, plaque reduction neutralization tests (PRNT).

METHODS

We followed the PRISMA statement for a systematic literature search and methods for conducting and reporting systematic reviews and meta-analyses recommended by the Cochrane Screening and Diagnostic Tests Methods Group. We identified studies through PubMed and Embase electronic databases and included serologic studies detecting measles virus IgG antibodies among participants of any age from the same source population that reported an index (any EIA or multiple bead-based assays, MBA) and reference test (PRNT) using sera, whole blood, or plasma. Measures of diagnostic accuracy with 95% confidence intervals (CI) were abstracted for each study result, where reported.

RESULTS

We identified 550 unique publications and identified 36 eligible studies for analysis. We classified studies as high, medium, or low quality; results from high quality studies are reported. Because most high quality studies used the Siemens Enzygnost EIA kit, we generate individual and pooled diagnostic accuracy estimates for this assay separately. Median sensitivity of the Enzygnost EIA was 92.1% [IQR = 82.3, 95.7]; median specificity was 96.9 [93.0, 100.0]. Pooled sensitivity and specificity from studies using the Enzygnost kit were 91.6 (95%CI: 80.7,96.6) and 96.0 (95%CI: 90.9,98.3), respectively. The sensitivity of all other EIA kits across high quality studies ranged from 0% to 98.9% with median (IQR) = 90.6 [86.6, 95.2]; specificity ranged from 58.8% to 100.0% with median (IQR) = 100.0 [88.7, 100.0].

CONCLUSIONS

Evidence on the diagnostic accuracy of currently available measles IgG EIAs is variable, insufficient, and may not be fit for purpose for serosurveillance goals. Additional studies evaluating the diagnostic accuracy of measles EIAs, including MBAs, should be conducted among diverse populations and settings (e.g., vaccination status, elimination/endemic status, age groups).

Vaccine Preventable Disease Seroprevalence in a Nationwide Assessment of Timor-Leste (VASINA-TL): study protocol for a population-representative cross-sectional serosurvey

INTRODUCTION

Historic disruption in health infrastructure combined with data from a recent vaccine coverage survey suggests there are likely significant immunity gaps to vaccine preventable diseases and high risk of outbreaks in Timor-Leste. Community-based serological surveillance is an important tool to augment understanding of population-level immunity achieved through vaccine coverage and/or derived from prior infection.

METHODS AND ANALYSIS

This national population-representative serosurvey will take a three-stage cluster sample and aims to include 5600 individuals above 1 year of age. Serum samples will be collected by phlebotomy and analysed for measles IgG, rubella IgG, SARS-CoV-2 antispike protein IgG, hepatitis B surface antibody and hepatitis B core antigen using commercially available chemiluminescent immunoassays or ELISA. In addition to crude prevalence estimates and to account for differences in Timor-Leste's age structure, stratified age-standardised prevalence estimates will be calculated, using Asia in 2013 as the standard population. Additionally, this survey will derive a national asset of serum and dried blood spot samples which can be used for further investigation of infectious disease seroepidemiology and/or validation of existing and novel serological assays for infectious diseases.

ETHICS AND DISSEMINATION

Ethical approval has been obtained from the Research Ethics and Technical Committee of the Instituto Nacional da Saúde, Timor-Leste and the Human Research Ethics Committee of the Northern Territory Department of Health and Menzies School of Health Research, Australia. Co-designing this study with Timor-Leste's Ministry-of-Health and other relevant partner organisations will allow immediate translation of findings into public health policy, which may include changes to routine immunisation service delivery and/or plans for supplementary immunisation activities.

Effect of remdesivir post-exposure prophylaxis and treatment on pathogenesis of measles in rhesus macaques

Measles is a systemic disease initiated in the respiratory tract with widespread measles virus (MeV) infection of lymphoid tissue. Mortality can be substantial, but no licensed antiviral therapy is available. We evaluated both post-exposure prophylaxis and treatment with remdesivir, a broad-spectrum antiviral, using a well-characterized rhesus macaque model of measles. Animals were treated with intravenous remdesivir for 12 days beginning either 3 days after intratracheal infection (post-exposure prophylaxis, PEP) or 11 days after infection at the onset of disease (late treatment, LT). As PEP, remdesivir lowered levels of viral RNA in peripheral blood mononuclear cells, but RNA rebounded at the end of the treatment period and infectious virus was continuously recoverable. MeV RNA was cleared more rapidly from lymphoid tissue, was variably detected in the respiratory tract, and not detected in urine. PEP did not improve clinical disease nor lymphopenia and reduced the antibody response to infection. In contrast, LT had little effect on levels of viral RNA or the antibody response but also did not decrease clinical disease. Therefore, remdesivir transiently suppressed expression of viral RNA and limited dissemination when provided as PEP, but virus was not cleared and resumed replication without improvement in the clinical disease parameters evaluated.

Long-term measles antibody profiles following different vaccine schedules in China, a longitudinal study

Characterizing the long-term kinetics of maternally derived and vaccine-induced measles immunity is critical for informing measles immunization strategies moving forward. Based on two prospective cohorts of children in China, we estimate that maternally derived immunity against measles persists for 2.4 months. Following two-dose series of measles-containing vaccine (MCV) at 8 and 18 months of age, the immune protection against measles is not lifelong, and antibody concentrations are extrapolated to fall below the protective threshold of 200 mIU/ml at 14.3 years. A catch-up MCV dose in addition to the routine doses between 8 months and 5 years reduce the cumulative incidence of seroreversion by 79.3-88.7% by the age of 6 years. Our findings also support a good immune response after the first MCV vaccination at 8 months. These findings, coupled with the effectiveness of a catch-up dose in addition to the routine doses, could be instrumental to relevant stakeholders when planning routine immunization schedules and supplemental immunization activities.

Measles Serostatus in Mothers and Their Newborns in Antioquia, Colombia: Implications for Measles Elimination

To describe the serostatus of measles IgG antibodies in pregnant women and newborns, placental transfer, and factors that determine being below the threshold of 150 mIU/mL, a cross-sectional study was conducted. Blood samples of 790 pregnant women at the time of delivery and 734 umbilical cord samples were analyzed from eight hospitals in the Aburrá Valley of Antioquia, Colombia. Measles IgG antibody measurement was performed with ELISA. The proportion of individuals with antibodies < 150 mIU/mL was 13.9% (95% CI: 12.2-15.8) in pregnant women and 11.1% (95% CI: 9.2-13.4) in newborns. The geometric mean of the antibody level of the pregnant women was 552 mIU/mL (95% CI: 504-605) and in the umbilical cord 662 mIU/mL (95% CI: 604-727). A positive correlation between pregnant woman and umbilical cord antibodies was found. The median ratio of measles IgG antibodies in umbilical cord/pregnant woman was 1.22 for all participants. A seroprevalence below the threshold of 150 mIU/mL was found in newborns whose mothers were born between 1983 and 1994, compared with those born before that period, when exposure to the wildtype virus was common (adjusted prevalence ratio: 3.6, 95% CI: 1.3-9.6). These findings suggest that there are gaps in measles immunity among women of childbearing age, before pregnancy. To close this immune gap and support efforts to maintain measles control, serological screening for measles antibodies should be routinely included in reproductive health and antenatal care programs to identify women without immunity who should be vaccinated before pregnancy or after delivery.

Measles seroprevalence in human immunodeficiency virus-infected adults born in the era of measles vaccination

OBJECTIVE

Widespread use of the measles vaccine should lead to the elimination of this disease. Here, we study the seroprevalence of measles in a cohort of adults living with HIV born after the introduction of measles vaccine in France and attempt to identify risk factors for the absence of serum measles antibody.

DESIGN

In this multi-centre cross-sectional study, adult outpatients born after 1980 were screened for the presence of measles IgG antibody. Demographic and clinical data were obtained from the standardized electronic medical record system. Univariate and multivariate logistic regressions were performed to identify factors associated with the absence of measles antibodies.

RESULTS

Between April 2019 and April 2020, 648 participants were enrolled. The median age was 33 years, 53.6% were born outside of France, and 74% were considered as socially deprived. Plasma HIV RNA was undetectable in 86% of patients. Among 603 evaluable patients, measles serology was positive in 87.2%. Only 81.8% of the patients with documented vaccination tested positive for measles IgG. Younger age was significantly associated with the absence of measles serum antibodies ( P  = 0.004 for each 10-year lower), as was birth in France ( P  < 0.001) and absence of social vulnerability ( P  = 0.04).

CONCLUSION

The current study revealed a low seroprevalence of measles compared with that previously reported in France 6 years earlier and to the expected rate to achieve herd immunity. Checking vaccination record should be systematically carried out in patients living with HIV to fill the immunity gaps.

Identifying immunity gaps for measles using Belgian serial serology data

Vaccine-preventable diseases, such as measles, have been re-emerging in countries with moderate to high vaccine uptake. It is increasingly important to identify and close immunity gaps and increase coverage of routine childhood vaccinations, including two doses of the measles-mumps-rubella vaccine (MMR). Here, we present a simple cohort model relying on a Bayesian approach to evaluate the evolution of measles seroprevalence in Belgium using the three most recent cross-sectional serological survey data collections (2002, 2006 and 2013) and information regarding vaccine properties. We find measles seroprevalence profiles to be similar for the different regions in Belgium. These profiles exhibit a drop in seroprevalence in birth cohorts that were offered vaccination at suboptimal coverages in the first years after routine vaccination has been started up. This immunity gap is observed across all cross-sectional survey years, although it is more pronounced in survey year 2013. At present, the COVID-19 pandemic could negatively impact the immunization coverage worldwide, thereby increasing the need for additional immunization programs in groups of children that are impacted by this. Therefore, it is now even more important to identify existing immunity gaps and to sustain and reach vaccine-derived measles immunity goals.

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.

Does infection with or vaccination against SARS-CoV-2 lead to lasting immunity?

Many nations are pursuing the rollout of SARS-CoV-2 vaccines as an exit strategy from unprecedented COVID-19-related restrictions. However, the success of this strategy relies critically on the duration of protective immunity resulting from both natural infection and vaccination. SARS-CoV-2 infection elicits an adaptive immune response against a large breadth of viral epitopes, although the duration of the response varies with age and disease severity. Current evidence from case studies and large observational studies suggests that, consistent with research on other common respiratory viruses, a protective immunological response lasts for approximately 5-12 months from primary infection, with reinfection being more likely given an insufficiently robust primary humoral response. Markers of humoral and cell-mediated immune memory can persist over many months, and might help to mitigate against severe disease upon reinfection. Emerging data, including evidence of breakthrough infections, suggest that vaccine effectiveness might be reduced significantly against emerging variants of concern, and hence secondary vaccines will need to be developed to maintain population-level protective immunity. Nonetheless, other interventions will also be required, with further outbreaks likely to occur due to antigenic drift, selective pressures for novel variants, and global population mobility.

Measles seroprevalence among Dutch travelling families

BACKGROUND

While measles vaccination is widely implemented in national immunisation programmes, measles incidence rates are increasing worldwide. Dutch inhabitants who were born between 1965-1975 may have fallen between two stools, lacking protection from a natural infection, and having missed the introduction of the measles vaccination schedule. With this study we aim to find the measles seroprevalence in travellers born between 1965 and 1975, compared to those born before 1965 and after 1975.

METHODS

Families travelling to Eastern Europe or outside Europe during the preceding year were recruited via Dutch secondary schools between 2016 and 2018. Their vaccination status was assessed using questionnaires, vaccination records and measles serology in dried blood spot (DBS) eluates. Measles virus antibody concentrations were determined with an ELISA (EUROIMMUNE®) and a subset was retested with a focus reduction neutralization assay (FRNT).

RESULTS

In 188 (79%) of the 239 available DBS eluates, the ELISA could detect sufficient measles virus-specific IgG antibodies. Of the negative samples that were retested with FRNT, 85% remained negative, resulting in an overall seroprevalence of 82% [95% CI 76-86]. Children had a lower seroprevalence (72%) than adults (87%). Travellers born between 1965 and 1975 were protected in 89%.

CONCLUSIONS

In this study, we report a measles seroprevalence of 82% among Dutch travelling families. Remarkably, seroprevalence rates were lowest in children (12-18 years) instead of travellers born between 1965 and 1975. Although a fraction of people without detectable antibodies may be protected by other immune mechanisms, these data suggest that measles (re)vaccination should be considered for travellers to endemic regions.

Measles immunity over two decades in two large Italian Regions: How far is the elimination goal?

In Italy, the inclusion of measles vaccine in children immunization schedule and the promotion of national mass vaccination campaigns increased measles vaccination coverage. However, measles outbreaks continue to occur increasingly involving adolescents and adults. The aim of this study was to evaluate the prevalence to measles antibody in a sample of Italian population between 1993 and 2018. Human serum samples from subjects aged 3-40 years were collected between 1993 and 2018 and tested for measles IgG antibodies by commercial ELISA. During the study period, the 3-10-year-old age group showed the most important change, with a significant increase in 2003-2007 in both seroprevalence and IgG levels, followed by a slow decrease. The 11-18-year-old age group showed relatively stable seroprevalence rates and IgG levels over the years. The 19-30-year-old group showed stable seroprevalence rates, albeit with a decrease in IgG levels. After a significant increase in 1999-2002, the 31-40-year-old age group had high seroprevalence rates and IgG levels. Despite efforts at national level for implementing measles vaccination, a large proportion of the population is still susceptible to measles. Even if vaccination coverage increases enough to achieve the level of immunization required for herd immunity in new birth cohorts, outbreaks will continue to occur if there are immunity gaps in older age groups. Establishing policies for measles vaccination targeting adult population is needed to close immunity gaps and reach the elimination goal.

Linked vaccination coverage surveys plus serosurveys among Ethiopian toddlers undertaken three years apart to compare coverage and serologic evidence of protection in districts implementing the RED-QI approach

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A seroprotective tetanus titer indicates a toddler has received pentavalent vaccine.

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Serosurveys document increased seroprevalence post-measles vaccination campaigns.

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Vaccination coverage/serosurveys can assess interventions to improve immunizations.

In low and middle-income countries, estimating the proportion of vaccinated toddlers in a population is important for controlling vaccine-preventable diseases by identifying districts where immunization services need strengthening. Estimates measured before and several years after specific interventions can assess program performance. However, employing different methods to derive vaccination coverage estimates often yield differing results.

Methods

Linked vaccination coverage surveys and seroprotection surveys performed among ~300 toddlers 12–23 months of age in districts (woredas), one per region, of Ethiopia (total, ~900 toddlers) in 2013 to estimate the proportion vaccinated with tetanus toxoid (a proxy for pentavalent vaccine) and measles vaccine. The surveys were followed by implementation of the Reaching Every District using Quality Improvement (RED-QI) approach to strengthen the immunization system.

Linked coverage/serosurveys were repeated in 2016 to assess effects of the interventions on vaccination coverage. Indicators included “documented coverage” (vaccination card and/or health facility register records) and “crude coverage” (documented plus parent/caretaker recall for children without cards). Seroprotection thresholds were IgG-ELISA tetanus antitoxin ≥0.05 IU/ml and plaque reduction neutralization (PRN) measles titers ≥120 mIU/ml.

Findings

Improved markers in 2016 over 2013 include coverage of pentavalent vaccination, vaccination timeliness, and fewer missed opportunities to vaccinate. In parallel, tetanus seroprotection increased in the 3 woredas from 59.6% to 79.1%, 72.9% to 83.7%, and 94.3 to 99.3%. In 2015, the Ethiopian government conducted supplemental measles mass vaccination campaigns in several regions including one that involved a project woreda and the campaign overlapped with the RED-QI intervention timeframe; protective measles PRN titers there rose from 31.0% to 50.0%.

Interpretation

The prevalence of seroprotective titers of tetanus antitoxin (stimulated by tetanus toxoid components within pentavalent vaccine) provides a reliable biomarker to identify children who received pentavalent vaccine. In the three study woredas, the RED-QI intervention appeared to improve immunization service delivery, as documented by enhanced pentavalent vaccine coverage, vaccination timeliness, and fewer missed vaccination opportunities. A measles mass vaccination campaign was followed by a markedly increased prevalence of measles PRN antibodies. Collectively, these observations suggest that wider implementation of RED-QI can strengthen immunization, and periodic linked vaccination surveys/serosurveys can monitor changes.

Correlates of Vaccine-Induced Protection against SARS-CoV-2

We are in the midst of a pandemic caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes the coronavirus disease 2019 (COVID-19). SARS-CoV-2 has caused more than two million deaths after one year of the pandemic. The world is experiencing a deep economic recession. Safe and effective vaccines are needed to prevent further morbidity and mortality. Vaccine candidates against COVID-19 have been developed at an unprecedented speed, with more than 200 vaccine candidates currently under investigation. Among those, 20 candidates have entered the clinical Phase 3 to evaluate efficacy, and three have been approved by the European Medicines Agency. The aim of immunization is to act against infection, disease and/or transmission. However, the measurement of vaccine efficacy is challenging, as efficacy trials need to include large cohorts with verum and placebo cohorts. In the future, this will be even more challenging as further vaccine candidates will receive approval, an increasing number of humans will receive vaccinations and incidence might decrease. To evaluate novel and second-generation vaccine candidates, randomized placebo-controlled trials might not be appropriate anymore. Correlates of protection (CoP) could be an important tool to evaluate novel vaccine candidates, but vaccine-induced CoP have not been clearly defined for SARS-CoV-2 vaccines. In this review, we report on immunogenicity against natural SARS-CoV-2 infection, vaccine-induced immune responses and discuss immunological markers that can be linked to protection. By discussing the immunogenicity and efficacy of forerunner vaccines, we aim to give a comprehensive overview of possible efficacy measures and CoP.

A challenging modified measles outbreak in vaccinated healthcare providers

BACKGROUND

Modified measles is rarely reported and thought to be an attenuated, less transmissible form of measles. The occupational safety and management of previously immunized healthcare providers (HCP) facing the global reemergence of measles is controversial and unclear.Aim: We report a measles outbreak with an unusual presentation among our vaccinated HCP at Saint George Hospital University Medical Center (SGHUMC) in Lebanon that occurred during a nationwide measles epidemic.

METHODS

We recorded cases at SGHUMC, a 333-bed tertiary-care center, from April 2018 to June 2018. We established a measles clinic for investigating all febrile patients. HCP exposure was linked to influx of index cases through our Emergency Department. Modified measles was defined as any variation in the classic presentation with a pinpoint/vesicular rash, documented exposure and evidence of prior immunity. We performed serology testing to diagnose and/or document immunity and implemented outbreak controls measures including PPE, airborne isolation, and mass notification.

FINDINGS

We diagnosed 8 inpatients with classic measles, and 9 affected HCP. We diagnosed 8 HCP with modified measles. One previously immunized HCP developed classic measles despite being immunized and having a positive IgG titer. Our contact tracing revealed a total of 96 exposed HCP with 27 HCP showing non-specific signs of viral illness. We required all the 9 affected HCP to undergo home isolation.

CONCLUSION

We believe it is a top priority to achieve adequate measles immunity, especially among HCP that are at the frontline of healthcare systems. This necessitates revisiting vaccination schedules and achieving seroprotective titers to reclaim proper herd immunity.

Seroepidemiologic Study Designs for Determining SARS-COV-2 Transmission and Immunity

Serologic studies are crucial for clarifying dynamics of the coronavirus disease pandemic. Past work on serologic studies (e.g., during influenza pandemics) has made relevant contributions, but specific conditions of the current situation require adaptation. Although detection of antibodies to measure exposure, immunity, or both seems straightforward conceptually, numerous challenges exist in terms of sample collection, what the presence of antibodies actually means, and appropriate analysis and interpretation to account for test accuracy and sampling biases. Successful deployment of serologic studies depends on type and performance of serologic tests, population studied, use of adequate study designs, and appropriate analysis and interpretation of data. We highlight key questions that serologic studies can help answer at different times, review strengths and limitations of different assay types and study designs, and discuss methods for rapid sharing and analysis of serologic data to determine global transmission of severe acute respiratory syndrome coronavirus 2.

Immune surveillance for vaccine-preventable diseases

INTRODUCTION

Immunesurveillance is an important tool to monitor the protection of the population against vaccine-preventable diseases, which is currently mostly based on the detection of specific serum antibodies. However, the landscape of immune surveillance is changing, driven by emerging and evolving pathogens, changes in the age distribution of the population and scientific understanding of protective immunity, necessitating a comprehensive review.

AREAS COVERED

To anticipate these changes, reliable and high-throughput detection of antibody levels is desired to enable screening in larger population settings. Antibody levels alone do not always equate with protection and may require additional functional testing of the antibodies or immune cell-based assays. In addition, the location (systemic or locally mucosal) of the infection and whether the antibodies are induced through infection or vaccination have implications for both immune protection and assessing immune status.

EXPERT COMMENTARY

In order to perform multicenter studies on many samples for multiple antigens, more validated reference materials and wider adoption of high-throughput techniques are needed. The field of serosurveillance will also benefit from better correlates of protection and understanding of (local) mechanisms of protection. Here we give an overview of the current state-of-the-art of serosurveillance and how the field could move forward.