Ten years of serological surveillance in England and Wales: methods, results, implications and action

Immunity of Canadians and risk of epidemics workshop - Conference report

On November 18-19, 2019, the Immunity of Canadians and Risk of Epidemics (iCARE) Network convened a workshop in Toronto, Ontario, Canada. The objectives of the workshop were to raise the profile of sero-epidemiology in Canada, discuss best practice and methodological innovations, and strategize on the future direction of sero-epidemiology work in Canada. In this conference report, we describe the presentations and discussions from the workshop, and comment on the impact of the COVID-19 pandemic on serosurveillance initiatives, both in Canada and abroad.

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).

Serosurveillance of SARS-CoV-2 in Welsh Blood Donors: Establishment of the surveillance system and results up to November 2022

BackgroundIn 2020, Wales experienced some of the highest rates of confirmed COVID-19 cases in Europe. We set up a serosurveillance scheme using residual samples from blood donations to inform the pandemic response in Wales.AimTo identify changes in SARS-CoV-2 antibody seroprevalence in Wales by time, demography and location.MethodsResidual samples from blood donations made in Wales between 29 June 2020 and 20 November 2022 were tested for antibodies to the nucleocapsid antigen (anti-N) of SARS-CoV-2, resulting from natural infection. Donations made between 12 April 2021 and 20 November 2022 were also tested for antibodies to the spike antigen (anti-S) occurring as a result of natural infection and vaccination.ResultsAge-standardised seroprevalence of anti-N antibodies in donors remained stable (4.4-5.5%) until November 2020 before increasing to 16.7% by February 2021. Trends remained steady until November 2021 before increasing, peaking in November 2022 (80.2%). For anti-S, seroprevalence increased from 67.1% to 98.6% between May and September 2021, then remained above 99%. Anti-N seroprevalence was highest in younger donors and in donors living in urban South Wales. In contrast, seroprevalence of anti-S was highest in older donors and was similar across regions. No significant difference was observed by sex. Seroprevalence of anti-N antibodies was higher in Black, Asian and other minority ethnicities (self-reported) compared with White donors, with the converse observed for anti-S antibodies.ConclusionWe successfully set up long-term serological surveillance of SARS-CoV-2 using residual samples from blood donations, demonstrating variation based on age, ethnicity and location.

Lessons learned from the implementation of integrated serosurveillance of communicable diseases in the Americas

Objective

Systematize the experience and identify challenges and lessons learned in the implementation of an initiative for integrated serosurveillance of communicable diseases using a multiplex bead assay in countries of the Americas.

Methods

Documents produced in the initiative were compiled and reviewed. These included concept notes, internal working papers, regional meetings reports, and survey protocols from the three participating countries (Mexico, Paraguay, and Brazil) and two additional countries (Guyana and Guatemala) where serology for several communicable diseases was included in neglected tropical diseases surveys. Information was extracted and summarized to describe the experience and the most relevant challenges and lessons learned.

Results

Implementing integrated serosurveys requires interprogrammatic and interdisciplinary work teams for the design of survey protocols to respond to key programmatic questions aligned to the needs of the countries. Valid laboratory results are critical and rely on the standardized installment and roll-out of laboratory techniques. Field teams require adequate training and supervision to properly implement survey procedures. The analysis and interpretation of serosurveys results should be antigen-specific, contextualizing the responses for each disease, and triangulated with programmatic and epidemiological data for making decisions tailored to specific population socioeconomic and ecologic contexts.

Conclusions

Integrated serosurveillance as a complementary tool for functional epidemiological surveillance systems is feasible to use and key components should be considered: political engagement, technical engagement, and integrated planning. Aspects such as designing the protocol, selecting target populations and diseases, laboratory capacities, anticipating the capacities to analyze and interpret complex data, and how to use it are key.

Estimating the Transmissibility of Mumps: A Modelling Study in Wuhan City, China

Despite the adoption of a national immunization program in China, the incidence of mumps remains high. This study aimed to describe the epidemiological characteristics, including the time, region, occupation, and age, of mumps in Wuhan from 2005 to 2018 and to evaluate its transmissibility. In this study, the susceptible-exposed-infectious-asymptomatic-recovered (SEIAR) model fitted the actual incidence data of mumps. The effective reproduction number (R t ) was used to evaluate and compare the transmission capacity in different areas. From 2005 to 2018, there were 36,415 cases. The incidence of mumps was highest among people aged 5-10 years (460.02 per 100,000). The SEIAR model fitted the reported mumps data well (P < 0.01). The median transmissibility (R t ) was 1.04 (range = 0-2.50). There were two peak spreads every year (from March to May and from October to December). The R t peak always appeared in the first 2 months of the peak incidence rate. The peak time of the epidemic spread of mumps was 1-2 months earlier than the peak incidence rate. The prevention and control measures of vaccination for children aged 5-10 years should be taken before the peak transmission capacity each year, 2 months before the peak of the outbreak, to reduce the spread of mumps.

Population (Antibody) Testing for COVID-19-Technical Challenges, Application and Relevance, an English Perspective

In the UK, population virus or antibody testing using virus swabs, serum samples, blood spots or oral fluids has been performed to a limited extent for several diseases including measles, mumps, rubella and hepatitis and HIV. The collection of population-based infection and immunity data is key to the monitoring of disease prevalence and assessing the effectiveness of interventions such as behavioural modifications and vaccination. In particular, the biological properties of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) and its interaction with the human host have presented several challenges towards the development of population-based immunity testing. Measuring SARS-CoV-2 immunity requires the development of antibody assays of acceptable sensitivity and specificity which are capable of accurately detecting seroprevalence and differentiating protection from non-protective responses. Now that anti-COVID-19 vaccines are becoming available there is a pressing need to measure vaccine efficacy and the development of herd immunity. The unprecedented impact of the SARS-CoV-2 pandemic in the UK in terms of morbidity, mortality, and economic and social disruption has mobilized a national scientific effort to learn more about this virus. In this article, the challenges of testing for SARS-CoV-2 infection, particularly in relation to population-based immunity testing, will be considered and examples given of relevant national level studies.

Severe Acute Respiratory Syndrome Coronavirus 2 Serosurveillance in a Patient Population Reveals Differences in Virus Exposure and Antibody-Mediated Immunity According to Host Demography and Healthcare Setting

Identifying drivers of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) exposure and quantifying population immunity is crucial to prepare for future epidemics. We performed a serial cross-sectional serosurvey throughout the first pandemic wave among patients from the largest health board in Scotland. Screening of 7480 patient serum samples showed a weekly seroprevalence ranging from 0.10% to 8.23% in primary and 0.21% to 17.44% in secondary care, respectively. Neutralization assays showed that highly neutralizing antibodies developed in about half of individuals who tested positive with enzyme-linked immunosorbent assay, mainly among secondary care patients. We estimated the individual probability of SARS-CoV-2 exposure and quantified associated risk factors. We show that secondary care patients, male patients, and 45–64-year-olds exhibit a higher probability of being seropositive. The identification of risk factors and the differences in virus neutralization activity between patient populations provided insights into the patterns of virus exposure during the first pandemic wave and shed light on what to expect in future waves.

Estimating force of infection from serologic surveys with imperfect tests

BACKGROUND

The force of infection, or the rate at which susceptible individuals become infected, is an important public health measure for assessing the extent of outbreaks and the impact of control programs.

METHODS AND FINDINGS

We present Bayesian methods for estimating force of infection using serological surveys of infections which produce a lasting immune response, accounting for imperfections of the test, and uncertainty in such imperfections. In this estimation, the sensitivity and specificity can either be fixed, or belief distributions of their values can be elicited to allow for uncertainty. We analyse data from two published serological studies of dengue, one in Colombo, Sri Lanka, with a single survey and one in Medellin, Colombia, with repeated surveys in the same individuals. For the Colombo study, we illustrate how the inferred force of infection increases as the sensitivity decreases, and the reverse for specificity. When 100% sensitivity and specificity are assumed, the results are very similar to those from a standard analysis with binomial regression. For the Medellin study, the elicited distribution for sensitivity had a lower mean and higher variance than the one for specificity. Consequently, taking uncertainty in sensitivity into account resulted in a wide credible interval for the force of infection.

CONCLUSIONS

These methods can make more realistic estimates of force of infection, and help inform the choice of serological tests for future serosurveys.

Influenza and Respiratory Virus Surveillance, Vaccine Uptake, and Effectiveness at a Time of Cocirculating COVID-19: Protocol for the English Primary Care Sentinel System for 2020-2021

Background

The Oxford–Royal College of General Practitioners (RCGP) Research and Surveillance Centre (RSC) and Public Health England (PHE) are commencing their 54th season of collaboration at a time when SARS-CoV-2 infections are likely to be cocirculating with the usual winter infections.

Objective

The aim of this study is to conduct surveillance of influenza and other monitored respiratory conditions and to report on vaccine uptake and effectiveness using nationally representative surveillance data extracted from primary care computerized medical records systems. We also aim to have general practices collect virology and serology specimens and to participate in trials and other interventional research.

Methods

The RCGP RSC network comprises over 1700 general practices in England and Wales. We will extract pseudonymized data twice weekly and are migrating to a system of daily extracts. First, we will collect pseudonymized, routine, coded clinical data for the surveillance of monitored and unexpected conditions; data on vaccine exposure and adverse events of interest; and data on approved research study outcomes. Second, we will provide dashboards to give general practices feedback about levels of care and data quality, as compared to other network practices. We will focus on collecting data on influenza-like illness, upper and lower respiratory tract infections, and suspected COVID-19. Third, approximately 300 practices will participate in the 2020-2021 virology and serology surveillance; this will include responsive surveillance and long-term follow-up of previous SARS-CoV-2 infections. Fourth, member practices will be able to recruit volunteer patients to trials, including early interventions to improve COVID-19 outcomes and point-of-care testing. Lastly, the legal basis for our surveillance with PHE is Regulation 3 of the Health Service (Control of Patient Information) Regulations 2002; other studies require appropriate ethical approval.

Results

The RCGP RSC network has tripled in size; there were previously 100 virology practices and 500 practices overall in the network and we now have 322 and 1724, respectively. The Oxford–RCGP Clinical Informatics Digital Hub (ORCHID) secure networks enable the daily analysis of the extended network; currently, 1076 practices are uploaded. We are implementing a central swab distribution system for patients self-swabbing at home in addition to in-practice sampling. We have converted all our primary care coding to Systematized Nomenclature of Medicine Clinical Terms (SNOMED CT) coding. Throughout spring and summer 2020, the network has continued to collect specimens in preparation for the winter or for any second wave of COVID-19 cases. We have collected 5404 swabs and detected 623 cases of COVID-19 through extended virological sampling, and 19,341 samples have been collected for serology. This shows our preparedness for the winter season.

Conclusions

The COVID-19 pandemic has been associated with a groundswell of general practices joining our network. It has also created a permissive environment in which we have developed the capacity and capability of the national primary care surveillance systems and our unique public health institute, the RCGP and University of Oxford collaboration.

Serogroup C Neisseria meningitidis disease epidemiology, seroprevalence, vaccine effectiveness and waning immunity, England, 1998/99 to 2015/16

Background

In 1999, the United Kingdom (UK) was the first country to introduce meningococcal group C (MenC) conjugate vaccination. This vaccination programme has evolved with further understanding, new vaccines and changing disease epidemiology.

Aim

To characterise MenC disease and population protection against MenC disease in England.

Methods

Between 1998/99–2015/16, surveillance data from England for laboratory-confirmed MenC cases were collated; using the screening method, we updated vaccine effectiveness (VE) estimates. Typing data and genomes were obtained from the Meningitis Research Foundation Meningococcus Genome Library and PubMLST Neisseria database. Phylogenetic network analysis of MenC cc11 isolates was undertaken. We compared bactericidal antibody assay results using anonymised sera from 2014 to similar data from 1996–1999, 2000–2004 and 2009.

Results

MenC cases fell from 883 in 1998/99 (1.81/100,000 population) to 42 cases (0.08/100,000 population) in 2015/16. Lower VE over time since vaccination was observed after infant immunisation (p = 0.009) and a single dose at 1–4 years (p = 0.03). After vaccination at 5–18 years, high VE was sustained for ≥ 8 years; 95.0% (95% CI: 76.0– 99.5%). Only 25% (75/299) children aged 1–14 years were seroprotected against MenC disease in 2014. Recent case isolates mostly represented two cc11 strains.

Conclusion

High quality surveillance has furthered understanding of MenC vaccines and improved schedules, maximising population benefit. The UK programme provides high direct and indirect protection despite low levels of seroprotection in some age groups. High-resolution characterisation supports ongoing surveillance of distinct MenC cc11 lineages.

Emergence of a Novel Coronavirus (COVID-19): Protocol for Extending Surveillance Used by the Royal College of General Practitioners Research and Surveillance Centre and Public Health England

Background

The Royal College of General Practitioners (RCGP) Research and Surveillance Centre (RSC) and Public Health England (PHE) have successfully worked together on the surveillance of influenza and other infectious diseases for over 50 years, including three previous pandemics. With the emergence of the international outbreak of the coronavirus infection (COVID-19), a UK national approach to containment has been established to test people suspected of exposure to COVID-19. At the same time and separately, the RCGP RSC’s surveillance has been extended to monitor the temporal and geographical distribution of COVID-19 infection in the community as well as assess the effectiveness of the containment strategy.

Objectives

The aims of this study are to surveil COVID-19 in both asymptomatic populations and ambulatory cases with respiratory infections, ascertain both the rate and pattern of COVID-19 spread, and assess the effectiveness of the containment policy.

Methods

The RCGP RSC, a network of over 500 general practices in England, extract pseudonymized data weekly. This extended surveillance comprises of five components: (1) Recording in medical records of anyone suspected to have or who has been exposed to COVID-19. Computerized medical records suppliers have within a week of request created new codes to support this. (2) Extension of current virological surveillance and testing people with influenza-like illness or lower respiratory tract infections (LRTI)—with the caveat that people suspected to have or who have been exposed to COVID-19 should be referred to the national containment pathway and not seen in primary care. (3) Serology sample collection across all age groups. This will be an extra blood sample taken from people who are attending their general practice for a scheduled blood test. The 100 general practices currently undertaking annual influenza virology surveillance will be involved in the extended virological and serological surveillance. (4) Collecting convalescent serum samples. (5) Data curation. We have the opportunity to escalate the data extraction to twice weekly if needed. Swabs and sera will be analyzed in PHE reference laboratories.

Results

General practice clinical system providers have introduced an emergency new set of clinical codes to support COVID-19 surveillance. Additionally, practices participating in current virology surveillance are now taking samples for COVID-19 surveillance from low-risk patients presenting with LRTIs. Within the first 2 weeks of setup of this surveillance, we have identified 3 cases: 1 through the new coding system, the other 2 through the extended virology sampling.

Conclusions

We have rapidly converted the established national RCGP RSC influenza surveillance system into one that can test the effectiveness of the COVID-19 containment policy. The extended surveillance has already seen the use of new codes with 3 cases reported. Rapid sharing of this protocol should enable scientific critique and shared learning.

International Registered Report Identifier (IRRID)

DERR1-10.2196/18606

Current Status of Mumps Virus Infection: Epidemiology, Pathogenesis, and Vaccine

Mumps is an important childhood infectious disease caused by mumps virus (MuV). We reviewed the epidemiology, pathogenesis, and vaccine development of mumps. Previous studies were identified using the key words “mumps” and “epidemiology”, “pathogenesis” or “vaccine” in MEDLINE, PubMed, Embase, Web of Science, and Google Scholar. We excluded the articles that were not published in the English language, manuscripts without abstracts, and opinion articles from the review. The number of cases caused by MuV decreased steeply after the introduction of the mumps vaccine worldwide. In recent years, a global resurgence of mumps cases in developed countries and cases of aseptic meningitis caused by some mumps vaccine strains have renewed the importance of MuV infection worldwide. The performance of mumps vaccination has become an important issue for controlling mumps infections. Vaccine development and routine vaccination are still effective measures to globally reduce the incidence of mumps infections. During outbreaks, a third of MMR vaccine is recommended for groups of persons determined by public authorities.

Seroprevalence of vaccine-preventable diseases among children and adolescents in Singapore: Results from the National Paediatric Seroprevalence Survey 2018

OBJECTIVES

The Ministry of Health (MOH), Singapore, conducted the National Paediatric Seroprevalence Survey 2018 (NPSS 2018) to estimate the latest immunity levels against measles, rubella, varicella, diphtheria, tetanus and hepatitis B, and the seroprevalence of chronic hepatitis B virus (HBV) carriage in children and adolescents in Singapore.

METHODS

The survey involved prospective collection of residual sera from 1,200 children and adolescents aged 1-17 years in two public acute hospitals. Enzyme-linked immunosorbent assays (EIA) or plague reduction neutralisation tests (PRNT) were used to determine the seroprevalence of the vaccine-preventable diseases.

RESULTS

Overall prevalence of measles and rubella antibodies among Singaporean children and adolescents aged 1-17 years were 98.2% (95% CI: 91.2-98.8%) and 94.8% (95% CI: 93.4-95.9%) respectively. 97.1% (95% CI: 96.0-97.9%) of subjects had at least basic protection against diphtheria, while 89.3% (95% CI: 87.5-91.0%) were protected against tetanus. The prevalence of chronic HBV carriage was 0.4% (95% CI: 0.2-1.0%), while 45.7% (95% CI: 42.9-48.5%) were immune against HBV. The seroprevalence for varicella antibodies was 52.9% (95% CI: 50.1-55.7%). Concordance between vaccination status and seroprevalence was observed for measles, rubella, diphtheria and tetanus.

CONCLUSION

Singapore's children and adolescents are well-protected against measles, rubella, diphtheria and tetanus. Continual efforts in ensuring high vaccination coverage should be sustained.

Serosurveillance for vaccine-preventable diseases: A look inside the pertussis experience

INTRODUCTION

Serological surveillance (serosurveillance) provides the most direct measure of herd immunity of vaccine-preventable diseases. Little is known about the opportunities and challenges of serosurveillance experiences, particularly pertussis.

OBJECTIVE

To describe the process of serosurveillance for vaccine-preventable diseases with an emphasis on the experience of pertussis in the metropolitan area of Antioquia (Valle de Aburrá) in 2015 and 2016 and analyze the contributions and challenges for its sustainability.

MATERIALS AND METHODS

We described the planning and conduction of serosurveillance of pertussis antibodies of mothers and in the umbilical cord at the time of delivery in eight hospitals based on random sampling and their capacity to advance the serosurveillance periodically. We compared the contributions and the challenges of this experience with other probabilistic and non-probabilistic programs.

RESULTS

We achieved the participation of hospitals and mothers respecting the delivery care process. We established a serum bank following ethical and technical guidelines. This program based on the random selection of hospitals and mothers has enabled the estimation of antibodies prevalence in mothers and in the umbilical cord, which has been possible given the high coverage of hospital care during childbirth at a lower cost and fewer risks than a population-based survey in conflictive areas. The main challenges for the sustainability of this program are the creation of stable jobs and access to funding and legal and methodological long-term frameworks.

CONCLUSIONS

Hospital serosurveillance as described is an option to monitor the impact of vaccination on the population. Our experience could be reproduced in other regions under similar conditions if the above-mentioned challenges are solved.

Increase in Enterovirus D68 Infections in Young Children, United Kingdom, 2006-2016

We determined the change in seroprevalence of enterovirus D68 (EV-D68) in the United Kingdom in age-stratified cohorts from 2006 to 2016, the period during which EV-D68 emerged as a cause of severe respiratory disease occasionally leading to paralysis. Infections were acquired primarily in infants and young children, and incidence was markedly higher in 2016.

The value of seroprevalence data as surveillance tool for Lyme borreliosis in the general population: the experience of Belgium

BACKGROUND

Serological surveillance, based on the measurement of the presence of specific antibodies in a given population, can be used in addition to traditional and routine disease surveillance methods. The added value of this has been largely documented for vaccine-preventable diseases, but to a lesser extent for vector-borne diseases. This study aimed to evaluate the utility of seroprevalence data as additional source of information on the epidemiology of Lyme borreliosis in Belgium.

METHODS

In total, 3215 residual blood samples collected in 2013-2015 were analysed with Liaison® Borrelia IgG kit (DiaSorin S.p.A, Saluggia, Italy). Positive and equivocal results were further examined with immunoblotting (recomLine Borrelia IgG kit, Mikrogen, Neuried, Germany). Crude prevalence estimates of equivocal and seropositive results were calculated and further adjusted accounting for clustered sampling and standardized for age, sex and population per province, according to the Belgian population structure in 2014. The effect of age, sex and region on seropositivity was assessed using log-binomial regression.

RESULTS

The overall weighted national seroprevalence for Borrelia burgdorferi sensu lato, adjusted for clustered sampling, age, sex and province was 1.06% (95%CI 0.67-1.67). Although not statistically significant, the highest prevalences were observed in men and in those younger than 15 years or older than 59 years of age. At provincial level, the seroprevalence estimates do not follow the geographical distribution of tick bites and diagnoses of Lyme borreliosis as detected through other surveillance systems.

CONCLUSIONS

Although the use of residual samples for seroprevalence estimates has several advantages, it seems to be a limited tool for serological surveillance of Lyme borreliosis in Belgium, other than follow-up of trends if repeated over time. A population-based sampling strategy might provide a more representative nationwide sample, but would be very time intensive and expensive. Seroprevalence studies within risk groups or risk areas in Belgium could provide a useful alternative approach to complement routine surveillance data of Lyme borreliosis.

Nationally-representative serostudy of dengue in Bangladesh allows generalizable disease burden estimates

Serostudies are needed to answer generalizable questions on disease risk. However, recruitment is usually biased by age or location. We present a nationally-representative study for dengue from 70 communities in Bangladesh. We collected data on risk factors, trapped mosquitoes and tested serum for IgG. Out of 5866 individuals, 24% had evidence of historic infection, ranging from 3% in the north to >80% in Dhaka. Being male (aOR:1.8, [95%CI:1.5–2.0]) and recent travel (aOR:1.3, [1.1–1.8]) were linked to seropositivity. We estimate that 40 million [34.3–47.2] people have been infected nationally, with 2.4 million ([1.3–4.5]) annual infections. Had we visited only 20 communities, seropositivity estimates would have ranged from 13% to 37%, highlighting the lack of representativeness generated by small numbers of communities. Our findings have implications for both the design of serosurveys and tackling dengue in Bangladesh.

Dengue is a mosquito-borne virus that infects millions of people each year. Often the countries most affected by the virus, such as Bangladesh, do not have the resources needed to tackle the disease. For resources sent to these countries to have the greatest impact, it is important to know which areas are most affected, and which subsets of the population are most at risk. A way to gather this information is to test for dengue virus antibodies a protein produced by the immune system in response to the infection in the blood of individuals. However, previous efforts to use these tests to understand dengue risk in communities have generally only been done in single locations, typically a major city, and the findings of these tests are unlikely to be applicable to the wider population.

Now, Salje et al. have visited 70 different communities from all around Bangladesh and used these tests on blood samples collected from over 5,000 individuals from a range of age-groups. From these measurements it was estimated that an average 2.4 million people are infected with dengue each year in Bangladesh, with major cities, such as Dhaka, experiencing more concentrated levels. The exposure to dengue outside major cities was much lower, and men, who tend to travel more, were found to be at greater risk of infection.

Salje et al. also showed that using a small number of communities to estimate national levels of infection led to misleading results. This highlights the danger of using information collected from a limited number of places to represent the effects of a disease on the wider population.

Public health agencies in Bangladesh will be able to use this information to tackle dengue more effectively, focusing on the areas and the populations most affected by the disease. In addition, the design and analytical approaches used in this study could be applied to other countries, and to different diseases.

Evaluation of measles immunity in Turkey: is it still a threat?

Background/aim

Measles is one of the important vaccine-preventable diseases with many complications in childhood. This study presents cross-sectional seroepidemiological data, beginning from neonatal cord blood in infants to children under 6 years of age, about waning of measles antibody and tries to suggest the proper time for measles immunization.

Materials and methods

A total of 564 blood samples consisting of neonatal cord blood and samples taken from infants and children at ages of 6, 9, 24–48, and 49–72 months were analyzed for measles seropositivity in a period of 6 months.

Results

Measles seropositivity rate was 72.5% in 109 cord blood samples, 2.6% in 117 infants of 6 months of age, and 3.6% in 111 infants of 9 months of age. Seropositivity was determined in 118 children at 24–48 months and in 109 children at 49–72 months and was 80.5% and 66%, respectively (P = 0.001). These children were vaccinated in the 12th month.

Conclusion

Though measles immunization coverage is 97% in Turkey, population immunity is somewhat lower than expected. Increases of measles cases in Europe and the refugee problem in the country could easily lead to outbreaks. Implementing the first dose of the immunization at 9 months may be an option.

Real-time modelling of a pandemic influenza outbreak

BACKGROUND

Real-time modelling is an essential component of the public health response to an outbreak of pandemic influenza in the UK. A model for epidemic reconstruction based on realistic epidemic surveillance data has been developed, but this model needs enhancing to provide spatially disaggregated epidemic estimates while ensuring that real-time implementation is feasible.

OBJECTIVES

To advance state-of-the-art real-time pandemic modelling by (1) developing an existing epidemic model to capture spatial variation in transmission, (2) devising efficient computational algorithms for the provision of timely statistical analysis and (3) incorporating the above into freely available software.

METHODS

Markov chain Monte Carlo (MCMC) sampling was used to derive Bayesian statistical inference using 2009 pandemic data from two candidate modelling approaches: (1) a parallel-region (PR) approach, splitting the pandemic into non-interacting epidemics occurring in spatially disjoint regions; and (2) a meta-region (MR) approach, treating the country as a single meta-population with long-range contact rates informed by census data on commuting. Model discrimination is performed through posterior mean deviance statistics alongside more practical considerations. In a real-time context, the use of sequential Monte Carlo (SMC) algorithms to carry out real-time analyses is investigated as an alternative to MCMC using simulated data designed to sternly test both algorithms. SMC-derived analyses are compared with 'gold-standard' MCMC-derived inferences in terms of estimation quality and computational burden.

RESULTS

The PR approach provides a better and more timely fit to the epidemic data. Estimates of pandemic quantities of interest are consistent across approaches and, in the PR approach, across regions (e.g. R₀ is consistently estimated to be 1.76-1.80, dropping by 43-50% during an over-summer school holiday). A SMC approach was developed, which required some tailoring to tackle a sudden 'shock' in the data resulting from a pandemic intervention. This semi-automated SMC algorithm outperforms MCMC, in terms of both precision of estimates and their timely provision. Software implementing all findings has been developed and installed within Public Health England (PHE), with key staff trained in its use.

LIMITATIONS

The PR model lacks the predictive power to forecast the spread of infection in the early stages of a pandemic, whereas the MR model may be limited by its dependence on commuting data to describe transmission routes. As demand for resources increases in a severe pandemic, data from general practices and on hospitalisations may become unreliable or biased. The SMC algorithm developed is semi-automated; therefore, some statistical literacy is required to achieve optimal performance.

CONCLUSIONS

Following the objectives, this study found that timely, spatially disaggregate, real-time pandemic inference is feasible, and a system that assumes data as per pandemic preparedness plans has been developed for rapid implementation.

FUTURE WORK RECOMMENDATIONS

Modelling studies investigating the impact of pandemic interventions (e.g. vaccination and school closure); the utility of alternative data sources (e.g. internet searches) to augment traditional surveillance; and the correct handling of test sensitivity and specificity in serological data, propagating this uncertainty into the real-time modelling.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN40334843.

FUNDING

This project was funded by the National Institute for Health Research (NIHR) Health Technology programme and will be published in full in Health Technology Assessment; Vol. 21, No. 58. See the NIHR Journals Library website for further project information. Daniela De Angelis was supported by the UK Medical Research Council (Unit Programme Number U105260566) and by PHE. She received funding under the NIHR grant for 10% of her time. The rest of her salary was provided by the MRC and PHE jointly.

SEROEPIDEMIOLOGY IN THE SURVEILLANCE OF VACCINE-PREVENTABLE DISEASES

Seroepidemiology is a potentially powerful tool for predicting and monitoring the effectiveness of specific prevention program using studies of antibody prevalence. The availability of a certified collection of blood serum (serum bank) allows to carry out a reliable assessment of population immunity to vaccine-preventable diseases; to determine the degree of epidemiological risk of the infection spread in various areas of the country; to implement short-term and long-term forecasting of changes in the situation on topical infections; to substantiate preventive measures in the system of biosafety for defined population groups and decreed contingents; to provide information necessary for making the optimal management decisions.

The immunogenicity and safety of a Hib-MenAC vaccine: a non-inferiority randomized, observer-blind trial in infants aged 3-5 months

BACKGROUND

The objective of this study was to evaluate the immunogenicity and safety of the novel combined Haemophilus influenzae type b-Neisseria meningitidis serogroup A and C-tetanus toxoid conjugate vaccine (Hib-MenAC).

METHODS

We conducted a non-inferiority, randomized, observer-blind, positive control clinical trial in 900 healthy infants aged between 3-5 months in Funing County, Jiangsu Province, China. Participants were randomly allocated, in a ratio of 2:1 (block = 6), to receive experimental combined Hib-MenAC vaccines co-administrated with placebo or the co-administration of licensed Hib vaccine and MenAC vaccine, according to a three-dose immunization schedule. The seroconversion of antibody titer against meningococcal serogroups A, C and Hib was the primary endpoint.

RESULTS

The experimental vaccines was non-inferior to the licensed two control vaccines. Participants receiving experimental Hib-MenAC vaccines showed a seroconversion rate of 99.0%, 96.1% and 97.7% for rSBA-MenA, rSBA-MenC and anti-PRP antibodies, respectively. The Hib-MenAC vaccine did not result in an increase in adverse reaction, and no serious adverse event was judged to be related to the vaccination.

CONCLUSIONS

The novel combined Hib-MenAC conjugate vaccine was safe and highly immunogenic in infants aged between 3 to 5 months.

Use of Pathogen-Specific Antibody Biomarkers to Estimate Waterborne Infections in Population-Based Settings

PURPOSE OF REVIEW

This review discusses the utility of pathogen-specific antibody biomarkers for improving estimates of the population burden of waterborne infections, assessing the fraction of infections that can be prevented by specific water treatments, and understanding transmission routes and the natural history and ecology of disease in different populations (including asymptomatic infection rates).

RECENT FINDINGS

We review recent literature on the application of pathogen-specific antibody response data to estimate incidence and prevalence of acute infections and their utility to assess the contributions of waterborne transmission pathways. Advantages and technical challenges associated with the use of serum versus minimally invasive salivary antibody biomarkers in cross-sectional and prospective surveys are discussed. We highlight recent advances and challenges and outline future directions for research, development, and application of antibody-based and other immunological biomarkers of waterborne infections.

Clustering of contacts relevant to the spread of infectious disease

OBJECTIVE

Infectious disease spread depends on contact rates between infectious and susceptible individuals. Transmission models are commonly informed using empirically collected contact data, but the relevance of different contact types to transmission is still not well understood. Some studies select contacts based on a single characteristic such as proximity (physical/non-physical), location, duration or frequency. This study aimed to explore whether clusters of contacts similar to each other across multiple characteristics could better explain disease transmission.

METHODS

Individual contact data from the POLYMOD survey in Poland, Great Britain, Belgium, Finland and Italy were grouped into clusters by the k medoids clustering algorithm with a Manhattan distance metric to stratify contacts using all four characteristics. Contact clusters were then used to fit a transmission model to sero-epidemiological data for varicella-zoster virus (VZV) in each country.

RESULTS AND DISCUSSION

Across the five countries, 9-15 clusters were found to optimise both quality of clustering (measured using average silhouette width) and quality of fit (measured using several information criteria). Of these, 2-3 clusters were most relevant to VZV transmission, characterised by (i) 1-2 clusters of age-assortative contacts in schools, (ii) a cluster of less age-assortative contacts in non-school settings. Quality of fit was similar to using contacts stratified by a single characteristic, providing validation that single stratifications are appropriate. However, using clustering to stratify contacts using multiple characteristics provided insight into the structures underlying infection transmission, particularly the role of age-assortative contacts, involving school age children, for VZV transmission between households.

Seroepidemiology: an underused tool for designing and monitoring vaccination programmes in low- and middle-income countries

Seroepidemiology, the use of data on the prevalence of bio-markers of infection or vaccination, is a potentially powerful tool to understand the epidemiology of infection before vaccination and to monitor the effectiveness of vaccination programmes. Global and national burden of disease estimates for hepatitis B and rubella are based almost exclusively on serological data. Seroepidemiology has helped in the design of measles, poliomyelitis and rubella elimination programmes, by informing estimates of the required population immunity thresholds for elimination. It contributes to monitoring of these programmes by identifying population immunity gaps and evaluating the effectiveness of vaccination campaigns. Seroepidemiological data have also helped to identify contributing factors to resurgences of diphtheria, Haemophilus Influenzae type B and pertussis. When there is no confounding by antibodies induced by natural infection (as is the case for tetanus and hepatitis B vaccines), seroprevalence data provide a composite picture of vaccination coverage and effectiveness, although they cannot reliably indicate the number of doses of vaccine received. Despite these potential uses, technological, time and cost constraints have limited the widespread application of this tool in low-income countries. The use of venous blood samples makes it difficult to obtain high participation rates in surveys, but the performance of assays based on less invasive samples such as dried blood spots or oral fluid has varied greatly. Waning antibody levels after vaccination may mean that seroprevalence underestimates immunity. This, together with variation in assay sensitivity and specificity and the common need to take account of antibody induced by natural infection, means that relatively sophisticated statistical analysis of data is required. Nonetheless, advances in assays on minimally invasive samples may enhance the feasibility of including serology in large survey programmes in low-income countries. In this paper, we review the potential uses of seroepidemiology to improve vaccination policymaking and programme monitoring and discuss what is needed to broaden the use of this tool in low- and middle-income countries.

A 16-year review of seroprevalence studies on measles and rubella

The determination of the seroprevalence of vaccine-preventable diseases is critical in monitoring the efficacy of vaccination programmes and to assess the gaps in population immunity but requires extensive organisation and is time and resource intensive. The results of the studies are frequently reported in peer-reviewed scientific, government and non-government publications. A review of scientific literature was undertaken to advise the development of WHO guidelines for the assessment of measles and rubella seroprevalence. A search of the National Library of Medicine's PubMed online publications using key words of 'measles', 'rubella', combined with 'serosurvey', 'seroprevalence', 'immunity' and 'population immunity' was conducted. A total of 97 articles published between January 1998 and June 2014 were retrieved, 68 describing serosurveys for measles and 58 serosurveys for rubella, conducted in 37 and 36 different countries respectively. Only 13 (19%) and 8 (14%) respectively were UN classified "least developed countries". The study sample varied markedly and included combinations of male and female infants, children, adolescents and adults. The study sizes also varied with 28% and 33% of measles and rubella studies respectively, having greater than 2000 participants. Microtitre plate enzyme immunoassays were used in 52 (76%) measles studies and 40 (69%) rubella studies. A total of 39 (57%) measles and 44 (76%) rubella studies reported quantitative test results. Seroprevalence ranged from 60.8% to 95.9% for measles and 53.0% to 99.3% for rubella studies. The review highlighted that infants lost maternally-acquired immunity within 9months of birth and were unprotected until vaccination. Two groups at higher risk of infection were identified: young adults between the ages of 15 and 30years and immigrants.

Epidemiology of Lyme Disease, Nova Scotia, Canada, 2002-2013

Nova Scotia has the highest reported incidence in Canada, but risk is localized to identified disease-endemic regions.

Ixodes scapularis ticks, which transmit Borreliaburgdorferi, the causative agent of Lyme disease (LD), are endemic to at least 6 regions of Nova Scotia, Canada. To assess the epidemiology and prevalence of LD in Nova Scotia, we analyzed data from 329 persons with LD reported in Nova Scotia during 2002–2013. Most patients reported symptoms of early localized infection with rash (89.7%), influenza-like illness (69.6%), or both; clinician-diagnosed erythema migrans was documented for 53.2%. In a separate serosurvey, of 1,855 serum samples screened for antibodies to B.burgdorferi, 2 were borderline positive (both with an indeterminate IgG on Western blot), resulting in an estimated seroprevalence of 0.14% (95% CI 0.02%–0.51%). Although LD incidence in Nova Scotia has risen sharply since 2002 and is the highest in Canada (16/100,000 population in 2013), the estimated number of residents with evidence of infection is low, and risk is localized to currently identified LD-endemic regions.

HPV Serology Testing Confirms High HPV Immunisation Coverage in England

Background

Reported human papillomavirus (HPV) vaccination coverage in England is high, particularly in girls offered routine immunisation at age 12 years. Serological surveillance can be used to validate reported coverage and explore variations within it and changes in serological markers over time.

Methods

Residual serum specimens collected from females aged 15–19 years in 2010–2011 were tested for anti-HPV16 and HPV18 IgG by ELISA. Based on these results, females were classified as follows: seronegative, probable natural infection, probable vaccine-induced seropositivity, or possible natural infection/possible vaccine-induced seropositivity. The proportion of females with vaccine-induced seropositivity was compared to the reported vaccination coverage.

Results

Of 2146 specimens tested, 1380 (64%) were seropositive for both types HPV16 and HPV18 and 159 (7.4%) positive for only one HPV type. The IgG concentrations were far higher for those positive for both HPV types than those positive for only one HPV type. 1320 (62%) females were considered to have probable vaccine-induced seropositivity. Among vaccine-induced seropositives, antibody concentrations declined with increasing age at vaccination and increasing time since vaccination.

Conclusions

The proportion of females with vaccine-induced seropositivity was closest to the reported 3-dose coverage in those offered the vaccination at younger ages, with a greater discrepancy in the older females. This suggests either some under-reporting of immunisations of older females and/or that partial vaccination (i.e. one- or two-doses) has provided high antibody responses in 13–17 year olds.

C. trachomatis Pgp3 antibody prevalence in young women in England, 1993-2010

Seroepidemiology of chlamydia can offer study opportunities and insights into cumulative risk of exposure that may contribute to monitoring the frequency of, and control of, genital chlamydia-the most commonly diagnosed STI in England. We undertook retrospective anonymous population-based cross-sectional surveys using an indirect IgG ELISA for chlamydia Pgp3 antibody. Sera from 4,732 women aged 17-24 years were tested. Samples were taken at 3-yearly intervals between 1993 and 2002, a period during which other data suggest chlamydia transmission may have been increasing, and from each year between 2007 and 2010. Seroprevalence increased in 17-24 year olds over time between 1993 and 2002. Between 2007 and 2010, age-standardised seroprevalence among 17-24 year olds decreased from 20% (95% CI: 17-23) to 15% (95%CI 12-17) (p = 0.0001). The biggest drop was among 20 to 21 year olds, where seroprevalence decreased from 21% in 2007 to 9% in 2010 (p = 0.002). These seroprevalence data reflect some known features of the epidemiology of chlamydia infection, and show that exposure to antibody-inducing chlamydia infection has declined in recent years. This decline was concurrent with increasing rates of screening for asymptomatic chlamydia. Serology should be explored further as a tool for evaluation of chlamydia control, including chlamydia screening programmes.

Correlated infections: quantifying individual heterogeneity in the spread of infectious diseases

In this paper, we propose new methods for investigating the extent of heterogeneity in effective contact rates relevant to the transmission of infections. These methods exploit the correlations between ages at infection for different infections within individuals. The methods are developed for serological surveys, which provide accessible individual data on several infections, and are applied to a wide range of infections. We find that childhood infections are often highly correlated within individuals in early childhood, with the correlations persisting into adulthood only for infections sharing a transmission route. We discuss 2 applications of the methods: 1) to making inferences about routes of transmission when these are unknown or uncertain and 2) to estimating epidemiologic parameters such as the basic reproduction number and the critical immunization threshold. Two examples of such applications are presented: elucidating the transmission route of polyomaviruses BK and JC and estimating the basic reproduction number and critical immunization coverage of varicella-zoster infection in Belgium, Italy, Poland, and England and Wales. We speculate that childhood correlations stem from confounding of different transmission routes and represent heterogeneity in childhood circumstances, notably nursery-school attendance. In contrast, it is suggested that correlations in adulthood are route-specific.

Influenza serological studies to inform public health action: best practices to optimise timing, quality and reporting

BACKGROUND

Serological studies can detect infection with a novel influenza virus in the absence of symptoms or positive virology, providing useful information on infection that goes beyond the estimates from epidemiological, clinical and virological data. During the 2009 A(H1N1) pandemic, an impressive number of detailed serological studies were performed, yet the majority of serological data were available only after the first wave of infection. This limited the ability to estimate the transmissibility and severity of this novel infection, and the variability in methodology and reporting limited the ability to compare and combine the serological data.

OBJECTIVES

  To identify best practices for conduct and standardisation of serological studies on outbreak and pandemic influenza to inform public policy.

METHODS/SETTING

An international meeting was held in February 2011 in Ottawa, Canada, to foster the consensus for greater standardisation of influenza serological studies.

RESULTS

Best practices for serological investigations of influenza epidemiology include the following: classification of studies as pre-pandemic, outbreak, pandemic or inter-pandemic with a clearly identified objective; use of international serum standards for laboratory assays; cohort and cross-sectional study designs with common standards for data collection; use of serum banks to improve sampling capacity; and potential for linkage of serological, clinical and epidemiological data. Advance planning for outbreak studies would enable a rapid and coordinated response; inclusion of serological studies in pandemic plans should be considered.

CONCLUSIONS

Optimising the quality, comparability and combinability of influenza serological studies will provide important data upon emergence of a novel or variant influenza virus to inform public health action.

Seroprevalence of hepatitis B virus infection among children and adolescents in Singapore, 2008-2010

A national pediatric survey was undertaken to determine the prevalence of hepatitis B virus markers in Singapore. The aim was to assess the impact of the national childhood immunization program against hepatitis B implemented for all newborns since 1987. The survey involved prospective collection of residual sera from Singapore residents aged 1-17 years attending inpatient services or day surgery in two public hospitals between August 2008 and July 2010. A total of 1,200 sera were collected comprising 400 in each of the three age groups of 1-6, 7-12, and 13-17 years. The sera were tested for hepatitis B surface antigen (HBsAg) and antibody to HBsAg (anti-HBs). Four of the 1,200 samples tested positive for HBsAg, giving an overall prevalence of 0.3%. One and three in the 7-12 years and 13-17 years age groups, respectively, were positive for HBsAg. About 40% possessed anti-HBs (≥10 mIU/ml); the antibody prevalence decreased significantly from 63.8% in children aged 1-6 years to 32.8% in 7-12 year olds, and 23.5% in 13-17 year olds (P < 0.0005). The successful implementation of the national childhood hepatitis B immunization program over the last two decades has resulted in a low prevalence of HBsAg among children and adolescents. Singapore has achieved the World Health Organization Western Pacific Region's goal in reducing the prevalence of chronic HBV infection to below 2% among children aged 5 years and older by 2012 and to below 1% by 2017.

Immunity to tetanus and diphtheria in the UK in 2009

INTRODUCTION

This study aimed to estimate the immunity of the UK population to tetanus and diphtheria, including the potential impact of new glycoconjugatate vaccines, and the addition of diphtheria to the school leaver booster in 1994.

METHODS

Residual sera (n=2697) collected in England in 2009/10 were selected from 18 age groups and tested for tetanus and diphtheria antibody. Results were standardised by testing a panel of sera (n=150) to enable comparison with a previously (1996) published serosurvey. Data were then standardised to the UK population.

RESULTS

In 2009, 83% of the UK population were protected (≥0.1 IU/mL) against tetanus compared to 76% in 1996 (p=0.079), and 75% had at least basic protection against diphtheria (≥0.01 IU/mL) in 2009 compared to 60% in 1996 (p<0.001). Higher antibody levels were observed in those aged 1-3 years in 2009 compared to 1996 for both tetanus and diphtheria. Higher diphtheria immunity was observed in those aged 16-34 years in 2009 compared to 1996 (geometric mean concentration [GMC] 0.15 IU/mL vs. 0.03 IU/mL, p<0.001). Age groups with the largest proportion of susceptible individuals to both tetanus and diphtheria in 2009 were <1 year old (>29% susceptible), 45-69 years (>20% susceptible) and 70+ years (>32% susceptible). Low immunity was observed in those aged 10-11 years (>19% susceptible), between the scheduled preschool and school leaver booster administration.

DISCUSSION

The current schedule appears to induce protective levels; increases in the proportions protected/GMCs were observed for the ages receiving vaccinations according to UK policy. Glycoconjugate vaccines appear to have increased immunity, in particular for diphtheria, in preschool age groups. Diphtheria immunity in teenagers and young adults has increased as a result of the addition of diphtheria to the school leaver booster. However, currently older adults remain susceptible, without any further opportunities for immunisations planned according to the present schedule.

Seroepidemiology of mumps in Europe (1996-2008): why do outbreaks occur in highly vaccinated populations?

Mumps outbreaks have recently been recorded in a number of highly vaccinated populations. We related seroprevalence, epidemiological and vaccination data from 18 European countries participating in The European Sero-Epidemiology Network (ESEN) to their risk of mumps outbreaks in order to inform vaccination strategies. Samples from national population serum banks were collected, tested for mumps IgG antibodies and standardized for international comparisons. A comparative analysis between countries was undertaken using age-specific mumps seroprevalence data and information on reported mumps incidence, vaccine strains, vaccination programmes and vaccine coverage 5-12 years after sera collection. Mean geometric mumps antibody titres were lower in mumps outbreak countries [odds ratio (OR) 0·09, 95% confidence interval (CI) 0·01-0·71)]. MMR1 vaccine coverage ⩾95% remained protective in a multivariable model (P < 0·001), as did an interval of 4-8 years between doses (OR 0·08, 95% CI 0·01-0·85). Preventing outbreaks and controlling mumps probably requires several elements, including high-coverage vaccination programmes with MMR vaccine with 4-8 years between doses.

Prevalence of serum bactericidal antibody to serogroup C Neisseria meningitidis in England a decade after vaccine introduction

Serogroup C meningococcal disease incidence and carriage declined rapidly in the United Kingdom after infant serogroup C conjugate vaccination was introduced in 1999, with catch-up vaccination for children under 18 years. Antibody levels and effectiveness waned quickly in children vaccinated at 2, 3, and 4 months of age. Therefore, in 2006, the current revised schedule of doses at 3, 4, and 12 months was introduced. This study assessed age-specific protection in 2009 compared with data from historical prevaccination and early postvaccination studies. Rabbit complement serum bactericidal antibody (SBA) was measured in anonymously banked serum samples collected in England in 2009 (n = 1,174), taking titers of ≥ 8 as protective. Age-stratified proportions of SBA titers that were ≥ 8 and geometric mean titers were compared. SBA titers varied markedly by birth cohort and time since vaccination. Overall, 35% of samples (95% confidence interval [CI], 33 to 38%) had titers that were ≥ 8. Only in cohorts eligible for catch-up vaccination did the majority of individuals have protective antibody levels. Antibody levels were higher in children eligible for vaccination at primary and secondary school ages, compared to those eligible below the age of 5 years. In those eligible for completed vaccination under the current schedule, protective levels were very modest and there was no evidence of superiority to cohorts that were eligible for the previous schedule. This supports a need for older childhood or adolescent booster vaccination in those previously eligible for vaccination during the infant, toddler, or preschool periods, to maintain direct protection and potentially enhance population immunity.

Seroprevalence of serum bactericidal antibodies against group W135 and Y meningococci in England in 2009

Serological surveillance has been used in the United Kingdom to inform vaccine policy for several infections, including those with group C meningococci. Meningococcal conjugate vaccines, containing capsular groups A, W135, and Y in addition to C, are now available, but their use in the United Kingdom is restricted to at-risk groups and travelers to areas of endemicity. The aim of this study was to establish a baseline for natural immunity for groups W135 and Y. Serum samples collected in 2009 from individuals of all ages were obtained from the Health Protection Agency Seroepidemiology Unit, which collects residual sera from participating laboratories across the country. Serum bactericidal antibody (SBA) activity against two reference strains, representing groups Y (strain M03 241125) and W135 (strain M01 240070), was determined with 1,191 sera using a standardized complement-mediated SBA assay, with complement derived from baby rabbits (rSBA). The age-specific geometric mean titers (GMTs) and percentages of individuals with rSBA titers of ≥ 8 were calculated, together with 95% confidence intervals (CI). Overall, 18.4% and 19.6% had rSBA titers of ≥ 8 for groups W135 and Y, respectively. Antibody prevalence varied by age. In general, rSBA titers were low for younger children, with serum samples from 7% and 13% of children under 5 years achieving titers of ≥ 8 against groups W135 and Y, respectively. GMTs peaked for 20- to 24-year-olds for group W135 (GMT, 7.1; 95% CI, 4.7, 10.9) and for 30- to 44-year-olds for group Y (GMT, 8.6; 95% CI, 5.9, 12.7). Unlike seroprevalence against group B meningococci, there was not an obvious peak in SBA titers in samples from teenagers. Natural immunity against group W135 and Y meningococci in England appears to be low.

Prevalence of human papillomavirus antibodies in males and females in England

BACKGROUND

Most studies of human papillomavirus (HPV) epidemiology have employed DNA testing, which measures current infections. Serum antibodies offer a longer-term marker of infection in individuals who seroconvert and can therefore provide additional information about the exposure of populations to HPV.

METHODS

Sera from a population-based sample of males and females aged 10 to 49 years, in England, were tested for type-specific HPV antibodies using a multiplexed competitive Luminex assay and previously defined cutoffs of 20, 16, 20, and 24 mMU mL for HPV 6, 11, 16, and 18, respectively. Seropositivity and geometric mean titers of seropositives were analyzed by HPV type, gender, and age. Catalytic models were developed to explore potential effects of antibody waning over time and changing risk of infection by age-cohort.

RESULTS

Seroprevalence for HPV 6, 11, 16, and 18 was 16.4%, 5.7%, 14.7%, and 6.3%, respectively, among females and 7.6%, 2.2%, 5.0%, and 2.0%, respectively, among males. Seroprevalence in females was significantly higher than males (P < 0.001 for all types) and showed a decline in older ages that was not seen in males. There was no evidence of declining antibody titers with increasing age. Model results suggest that cohort effects mediated through changes in sexual behavior better explain the observed trend in seroprevalence than waning antibodies over time.

CONCLUSIONS

Preimmunization HPV seroprevalence in England shows similar trends to reports from other developed countries. We find the lower seroprevalence in older females probably reflects changes in sexual behavior over the last few decades. This study provides baseline data to monitor the impact of the immunization programme.

The changing seroepidemiology of enterovirus 71 infection among children and adolescents in Singapore

BACKGROUND

Enterovirus 71 (EV71) has caused recurrent epidemics of hand, foot and mouth disease among children in Singapore. Between August 2008 and July 2010, we conducted a survey to estimate the seroprevalence of EV71 infection among children and adolescents aged 1-17 years. We compared our EV71 seroepidemiologic findings with a previous study conducted in 1996-1997.

METHODS

The survey involved the prospective collection of 1,200 residual sera from Singapore residents aged 1-17 years in two hospitals. Neutralizing antibodies to EV71 were detected by the microneutralization test. The geometric mean titer (GMT) of EV71 antibodies and 95% confidence intervals (CI) were calculated and compared by age groups. Statistical significance was taken as P < 0.05.

RESULTS

The overall EV71 antibody prevalence was 26.9% (95% CI: 24.5-29.5%). It increased significantly from 14.3% in children aged 1-6 years to 27.8% in those aged 7-12 years, and reached 38.8% in adolescents aged 13-17 years. The seroconversion rate differed by about 12% between the consecutive age groups. The GMT of EV71 antibodies was higher among primary school children aged 7-12 years in our study than that among the 6-12 year age group in the 1996-1997 study.

CONCLUSIONS

Higher antibody titers were observed in children aged 1-6 years than those in the other two age groups, indicating that most of the infections had been acquired during early childhood. EV71 infection is common among children and adolescents in Singapore, with 39% infected by the time they are in secondary school (13-17 years of age).

Dynamic epidemic model for influenza with clinical complications

OBJECTIVE

To incorporate clinical complications in the susceptible-infectious-recovered model to estimate parameters needed in dynamic changes of infectious diseases and to further evaluate the impact of disease-controlling methods.

METHODS

We developed a new extended epidemic model that incorporates of disease-related complications. This model was applied to empirical data on influenza during the epidemic season of 2001-2002 in Taipei County, Taiwan, to estimate the transmission parameters that were converted to the basic reproductive rate (R(0)). The proposed model, in conjunction with estimated parameters, was applied in quantifying the efficacy of different preventive strategies.

RESULTS

During the study period there were 5 outbreaks of influenza. The estimated transmission probability for outbreak 1 was 0.135, with corresponding estimate of R(0), 2.7; for outbreak 2, 0.165, with estimated R(0), 3.3; for outbreak 3, 0.15, with R(0), 4.5; for outbreak 4, 0.165, with R(0), 5; and for outbreak 5, 0.165, with R(0), 5. The efficacy of antiviral prophylaxis to reduce the total episodes was 18% (95% CI, 15%-21%) under the coverage rate of 30%, 31% (95% CI, 26%-36%) under the coverage rate of 50%, and 73% (95% CI, 59%-90%) under the coverage rate of 80%. The corresponding figures for the efficacy of vaccination were 17% (95% CI, 15%-20%), 41% (95% CI, 35%-48%), and 76% (95% CI, 61%-95%). Combination of both methods would yield efficacy of 32% (95% CI, 28%-38%), 59% (95% CI, 49%-71%), and 88% (95% CI, 66%-118%), respectively.

CONCLUSIONS

We demonstrate how to apply a novel extended model to empirical surveillance data of an influenza study for estimating parameters pertaining to dynamic changes in the infection process. These parameters were further used to evaluate the impact of antiviral prophylaxis alone, vaccination alone, or the use of both methods.

Are we hitting immunity targets? The 2006 age-specific seroprevalence of measles, mumps, rubella, diphtheria and tetanus in Belgium

Susceptibility to vaccine-preventable diseases in Belgium in 2006 was estimated from a serum survey. Immunoglobulins against measles, mumps, rubella (MMR) and diphtheria at all available ages (1-65 years), and against tetanus in >40-year-olds, were measured by ELISA. Age-standardized overall seronegativity for MMR was low (3·9%, 8·0%, 10·4%, respectively). However, the World Health Organization's targets for measles elimination were not met in 5- to 24-year-olds and about 1 in 7 women at childbearing age (15-39 years) were seronegative for rubella. In adults >40 years, tetanus immunity (87·2%, >0·16 IU/ml) largely exceeded diphtheria immunity (20-45%, >0·1 IU/ml). Despite free universal vaccination against MMR for more than 20 years and against diphtheria and tetanus for almost 60 years, our study revealed specific age groups remaining at risk for infection with these pathogens.

Low serum serotype-specific pneumococcal antibody concentrations in young children with Haemophilus influenzae serotype b (Hib) vaccine failure

Serotype-specific pneumococcal antibody concentrations were measured in 164 children with Hib vaccine failure prior to routine pneumococcal immunisation. Compared with age-matched controls, a higher proportion of cases had non-protective antibody concentrations (< 0.35 microg/ml) for 7/9 (78%) serotypes tested among 2-4 year-olds, 4/9 (44%) among 5-7 year-olds, 1/9 (11%) among 8-11 year-olds and 0/9 (0%) among 12-15 year-olds (chi(2) for trend=14.0, p=0.0002). Cases aged 2-4 years were also more likely to have non-protective antibody concentrations against more serotypes than controls, suggesting that children with Hib vaccine failure may have an intact but physiologically delayed ability to develop protective antibody concentrations against encapsulated organisms.

Incidence of 2009 pandemic influenza A H1N1 infection in England: a cross-sectional serological study

BACKGROUND

Knowledge of the age-specific prevalence of immunity from, and incidence of infection with, 2009 pandemic influenza A H1N1 virus is essential for modelling the future burden of disease and the effectiveness of interventions such as vaccination.

METHODS

In this cross-sectional serological survey, we obtained 1403 serum samples taken in 2008 (before the first wave of H1N1 infection) and 1954 serum samples taken in August and September, 2009 (after the first wave of infection) as part of the annual collection for the Health Protection Agency seroepidemiology programme from patients accessing health care in England. Antibody titres were measured by use of haemagglutination inhibition and microneutralisation assays. We calculated the proportion of samples with antibodies to pandemic H1N1 virus in 2008 by age group and compared the proportion of samples with haemagglutination inhibition titre 1:32 or more (deemed a protective response) before the first wave of infection with the proportion after the first wave.

FINDINGS

In the baseline serum samples from 2008, haemagglutination inhibition and microneutralisation antibody titres increased significantly with age (F test p<0.0001). The proportion of samples with haemagglutination inhibition titre 1:32 or more ranged from 1.8% (three of 171; 95% CI 0.6-5.0) in children aged 0-4 years to 31.3% (52 of 166; 24.8-38.7) in adults aged 80 years or older. In London and the West Midlands, the difference in the proportion of samples with haemagglutination inhibition titre equal to or above 1:32 between baseline and September, 2009, was 21.3% (95% CI 8.8-40.3) for children younger than 5 years of age, 42.0% (26.3-58.2) for 5-14-year-olds, and 20.6% (1.6-42.4) for 15-24-year-olds, with no difference between baseline and September in older age groups. In other regions, only children younger than 15 years showed a significant increase from baseline (6.3%, 1.8-12.9).

INTERPRETATION

Around one child in every three was infected with 2009 pandemic H1N1 in the first wave of infection in regions with a high incidence, ten times more than estimated from clinical surveillance. Pre-existing antibody in older age groups protects against infection. Children have an important role in transmission of influenza and would be a key target group for vaccination both for their protection and for the protection of others through herd immunity.

FUNDING

National Institute for Health Research Health Technology Assessment Programme.

The role of simple mathematical models in malaria elimination strategy design

Background

Malaria has recently been identified as a candidate for global eradication. This process will take the form of a series of national eliminations. Key issues must be considered specifically for elimination strategy when compared to the control of disease. Namely the spread of drug resistance, data scarcity and the adverse effects of failed elimination attempts. Mathematical models of various levels of complexity have been produced to consider the control and elimination of malaria infection. If available, detailed data on malaria transmission (such as the vector life cycle and behaviour, human population behaviour, the acquisition and decay of immunity, heterogeneities in transmission intensity, age profiles of clinical and subclinical infection) can be used to populate complex transmission models that can then be used to design control strategy. However, in many malaria countries reliable data are not available and policy must be formed based on information like an estimate of the average parasite prevalence.

Methods

A simple deterministic model, that requires data in the form of a single estimate of parasite prevalence as an input, is developed for the purpose of comparison with other more complex models. The model is designed to include key aspects of malaria transmission and integrated control.

Results

The simple model is shown to have similar short-term dynamic behaviour to three complex models. The model is used to demonstrate the potential of alternative methods of delivery of controls. The adverse effects on clinical infection and spread of resistance are predicted for failed elimination attempts. Since elimination strategies present an increased risk of the spread of drug resistance, the model is used to demonstrate the population level protective effect of multiple controls against this very serious threat.

Conclusion

A simple model structure for the elimination of malaria is suitable for situations where data are sparse yet strategy design requirements are urgent with the caveat that more complex models, populated with new data, would provide more information, especially in the long-term.