Kinetics of maternal antibodies against rubella and varicella in infants

Exploring the long-term seroprevalence of SARS-CoV-2 antibodies in infants born to women with clinical or laboratory-confirmed COVID-19

INTRODUCTION

Infants are at a higher risk of severe illness with COVID-19 infection compared to older children. While COVID-19 vaccination is not recommended for young infants, they can acquire maternally-derived anti-SARS-CoV-2 antibodies passively through the placenta and breastmilk. We described the persistence of infection-induced maternal antibodies in infant circulation at 9-12 months of age.

METHODOLOGY

This was a cross-sectional study nested within the INTERCOVID multinational cohort study. For each COVID positive pregnant woman, two unmatched consecutive COVID negative pregnant women were enrolled between April and September 2020. Women with a positive PCR test, radiographic signs consistent with COVID-19, or at least 2 predefined symptoms of COVID-19 were considered as COVID positive. For this nested cross-sectional study, all COVID positive and either one of the COVID negative participants recruited from the Aga Khan University, Pakistan were approached 9-12 months after delivery, and maternal and infant sera were collected for antibody detection.

RESULTS

Altogether, 83 mothers provided consent, of whom 32 (38.6 %) were COVID positive and 51 (61.4 %) were COVID negative during pregnancy. Anti-SARS-CoV-2 antibodies were present in 13 (41 %) infants born to COVID positive and 19 (39 %) infants born to COVID negative mothers (p = 0.87). The presence of reactive antibodies in infants at follow-up was associated with maternal antibodies at follow-up (OR:9.50, 95 % CI:2.03-44.42; p = 0.004). COVID infection occurred in 3 (6 %) infants born to COVID negative mothers while no infant born to a COVID positive mother had a history of infection (p = 0.27).

CONCLUSION

The presence of reactive anti-SARS-CoV-2 antibodies in infants at 9-12 months of age is associated with maternal seropositivity 9-12 months after delivery rather than maternal infection during pregnancy. Further studies are required to validate these findings and assess whether passive immunity in infants is protective against COVID-19 infection.

Genital VZV in a Third Trimester Pregnancy and the Critical Role of Interdisciplinary Planning

Introduction

Herpes simplex (HSV) and varicella zoster (VZV) viruses are harmful infectious agents in pregnancy due to their ability to impact maternal-fetal dyads through various modalities including vertical transmission, neonatal infection, and maternal morbidity. As a result, accurate diagnosis and prompt treatment of these infections in pregnancy is critical.

Case

A 19-year-old primigravida presented to our tertiary care center at 30 weeks' gestation with vulvar swelling, burning, and pain. Workup included direct PCR testing of a particularly erythematous area of the vulva which returned positive for VZV. The patient was treated with a 10-day course of acyclovir with resolution of her symptoms. She later had a full-term spontaneous vaginal delivery outside of the infectious window with no significant morbidity for either her or her neonate.

Conclusion

Although a rare presentation, the presence of a genital lesion or labial swelling during pregnancy warrants workup for VZV, particularly among patients known to be varicella nonimmune. If genital VZV is diagnosed during pregnancy, the development of contingency plans through interdisciplinary collaboration should be pursued to ensure a safe delivery and postpartum course for both the maternal-fetal dyad as well as other patients on the unit and the provider care team.

Life-threatening infections in human newborns: Reconciling age-specific vulnerability and interindividual variability

In humans, the interindividual variability of clinical outcome following exposure to a microorganism is immense, ranging from silent infection to life-threatening disease. Age-specific immune responses partially account for the high incidence of infection during the first 28 days of life and the related high mortality at population level. However, the occurrence of life-threatening disease in individual newborns remains unexplained. By contrast, inborn errors of immunity and their immune phenocopies are increasingly being discovered in children and adults with life-threatening viral, bacterial, mycobacterial and fungal infections. There is a need for convergence between the fields of neonatal immunology, with its in-depth population-wide characterization of newborn-specific immune responses, and clinical immunology, with its investigations of infections in patients at the cellular and molecular levels, to facilitate identification of the mechanisms of susceptibility to infection in individual newborns and the design of novel preventive and therapeutic strategies.

[Varicella vaccination, pregnancy and breastfeeding: The current situation]

The varicella vaccine is recommended for women with no history of varicella who are planning to become pregnant, as well as for post-pregnancy women, to prevent the occurrence of this illness and its severe complications, especially an embryopathy, when it occurs in a pregnant woman (congenital varicella syndrome). This live attenuated vaccine should not be administered during pregnancy, nor in the month preceding it. However, when this occurs inadvertently, the data collected on the outcomes of exposed pregnancies, although few in women seronegative at the time of vaccination, allow to reassure the patients to date, as no congenital varicella syndrome has been reported to date following accidental vaccination in early pregnancy. On the other hand, during breastfeeding, a woman may be vaccinated if there is an expected short- or medium-term benefit (varicella exposure, planned pregnancy…).

Repeated AAV9 Titer Determination in a Presymptomatic SMA Patient with Three SMN2 Gene Copies - A Case Report

Adeno-associated viruses (AAV) are well-suited to serve as gene transfer vectors. Onasemnogene abeparvovec uses AAV9 as virus vector. Previous exposure to wild-type AAVs or placental transfer of maternal AAV antibodies, however, can trigger an immune response to the vector virus which may limit the therapeutic effectiveness of gene transfer and impact safety. We present the case of a female patient with spinal muscular atrophy (SMA) and three survival motor neuron 2 (SMN2) gene copies. The infant had elevated titers of AAV9 antibodies at diagnosis at 9 days of age. Being presymptomatic at diagnosis, it was decided to retest the patient's AAV9 antibody titer at two-weekly intervals. Six weeks after initial diagnosis, a titer of 1:12.5 allowed treatment with onasemnogene abeparvovec. The presented case demonstrates that, provided the number of SMN2 gene copies and the absence of symptoms allow, onasemnogene abeparvovec therapy is feasible in patients with initially exclusionary AAV9 antibody titers of >1:50.

Maternal varicella antibodies in children aged less than one year: Assessment of antibody decay

OBJECTIVES

To investigate maternal antibody levels to varicella in infants <12 months of age in Ontario, Canada.

STUDY DESIGN

In this study, we included specimens from infants <12 months of age, born at ≥37 weeks gestational age, who had sera collected at The Hospital for Sick Children (Toronto, Canada) between 2014-2016. We tested sera using a glycoprotein-based enzyme-linked immunosorbent assay (gpELISA). We measured varicella susceptibility (antibody concentration <150mIU/mL) and mean varicella antibody concentration, and assessed the probability of susceptibility and concentration between one and 11 months of age using multivariable logistic regression and Poisson regression.

RESULTS

We found that 32% of 196 included specimens represented infants susceptible to varicella at one month of age, increasing to nearly 80% at three months of age. At six months of age, all infants were susceptible to varicella and the predicted mean varicella antibody concentration declined to 62 mIU/mL (95% confidence interval 40, 84), well below the threshold of protection.

CONCLUSIONS

We found that varicella maternal antibody levels wane rapidly in infants, leaving most infants susceptible by four months of age. Our findings have implications for the timing of first dose of varicella-containing vaccine, infection control measures, and infant post-exposure prophylaxis recommendations.

Passive transfer of alloantibodies through breast milk as a mediator of hemolytic anemia

BACKGROUND

Hemolytic disease of the fetus and newborn (HDFN) is characterized by destruction of fetal/neonatal red blood cells (RBCs) secondary to maternally derived antibodies, which are typically thought to be passively acquired via placental transfer. Few cases have examined the possibility of HDFN mediated by maternal antibodies passively transferred via breast milk.

METHODS

We describe two cases of persistent HDFN in infants potentially mediated by passively acquired antibodies via maternal breast milk. We discuss supporting and refuting evidence that may account for this possibility and describe testing methodology illustrating how maternal alloantibodies can be detected in breast milk.

RESULTS

In both cases, anti-D antibodies were detected in maternal breast milk. One patient experienced a significant decrease in anti-D plasma titer from 64 to 4 dilutions following 2 weeks of breastfeeding cessation. The other patient experienced a resolution of anemia without breastfeeding cessation.

CONCLUSION

There is a paucity of data regarding the lifespan of passively acquired RBC antibodies in neonatal circulation, with significant variation noted between passively acquired IgG based on studies utilizing intravenous immunoglobulin compared to studies of maternally-acquired antiviral IgG antibodies. While our data do not definitively implicate passive transfer of alloantibodies in breast milk as a mediator of HDFN, they do illustrate the need for further investigation into the mechanisms and kinetics of passively acquired antibodies in neonatal circulation.

Within-host modeling to measure dynamics of antibody responses after natural infection or vaccination: A systematic review

BACKGROUND

Within-host models describe the dynamics of immune cells when encountering a pathogen, and how these dynamics can lead to an individual-specific immune response. This systematic review aims to summarize which within-host methodology has been used to study and quantify antibody kinetics after infection or vaccination. In particular, we focus on data-driven and theory-driven mechanistic models.

MATERIALS

PubMed and Web of Science databases were used to identify eligible papers published until May 2022. Eligible publications included those studying mathematical models that measure antibody kinetics as the primary outcome (ranging from phenomenological to mechanistic models).

RESULTS

We identified 78 eligible publications, of which 8 relied on an Ordinary Differential Equations (ODEs)-based modelling approach to describe antibody kinetics after vaccination, and 12 studies used such models in the context of humoral immunity induced by natural infection. Mechanistic modeling studies were summarized in terms of type of study, sample size, measurements collected, antibody half-life, compartments and parameters included, inferential or analytical method, and model selection.

CONCLUSIONS

Despite the importance of investigating antibody kinetics and underlying mechanisms of (waning of) the humoral immunity, few publications explicitly account for this in a mathematical model. In particular, most research focuses on phenomenological rather than mechanistic models. The limited information on the age groups or other risk factors that might impact antibody kinetics, as well as a lack of experimental or observational data remain important concerns regarding the interpretation of mathematical modeling results. We reviewed the similarities between the kinetics following vaccination and infection, emphasising that it may be worth translating some features from one setting to another. However, we also stress that some biological mechanisms need to be distinguished. We found that data-driven mechanistic models tend to be more simplistic, and theory-driven approaches lack representative data to validate model results.

Varicella-Zoster Virus Prevalence among Pregnant Women: A European Epidemiological Review

Europe has faced a massive spread of the varicella-zoster virus through the years. Since the introduction of an effective vaccine, complications and severe forms of chickenpox have been restricted. Nevertheless, among the population, some categories need specific care, such as pregnant women, who present one of the most fragile conditions facing this infection, both for the mother and the fetus. In this review, we highlight how the varicella-zoster virus can be dangerous during pregnancy, underlining the problem of treatment and vaccination, and collect information about the European epidemiology among this particular category of women.

Optimizing the Live Attenuated Influenza A Vaccine Backbone for High-Risk Patient Groups

Together with inactivated influenza vaccines (IIV), live attenuated influenza vaccines (LAIV) are an important tool to prevent influenza A virus (IAV) illnesses in patients. LAIVs present the advantages to have a needle-free administration and to trigger a mucosal immune response. LAIV is approved for healthy 2- to 49-year old individuals. However, due to its replicative nature and higher rate of adverse events at-risk populations are excluded from the benefits of this vaccine. Using targeted mutagenesis, we modified the nonstructural protein 1 of the currently licensed LAIV in order to impair its ability to bind the host cellular protein CPSF30 and thus its ability to inhibit host mRNA poly-adenylation. We characterized our optimized LAIV (optiLAIV) in three different mouse models mimicking healthy and high-risk patients. Using a neonatal mouse model, we show faster clearance of our optimized vaccine compared to the licensed LAIV. Despite lower replication, optiLAIV equally protected mice against homosubtypic and hetesubtypic influenza strain challenges. We confirmed the safer profile of optiLAIV in Stat1^-/- mice (highly susceptible to viral infections) by showing no signs of morbidity compared to a 50% mortality rate observed following LAIV inoculation. Using a human nasal 3D tissue model, we showed an increased induction of ER stress-related genes following immunization with optiLAIV. Induction of ER stress was previously shown to improve antigen-specific immune responses and is proposed as the mechanism of action of the licensed adjuvant AS03. This study characterizes a safer LAIV candidate in two mouse models mimicking infants and severely immunocompromised patients and proposes a simple attenuation strategy that could broaden LAIV application and reduce influenza burden in high-risk populations. IMPORTANCE Live attenuated influenza vaccine (LAIV) is a needle-free, mucosal vaccine approved for healthy 2- to 49-year old individuals. Its replicative nature and higher rate of adverse events excludes at-risk populations. We propose a strategy to improve LAIV safety and explore the possibility to expand its applications in children under 2-year old and immunocompromised patients. Using a neonatal mouse model, we show faster clearance of our optimized vaccine (optiLAIV) compared to the licensed LAIV. Despite lower replication, optiLAIV equally protected mice against influenza virus challenges. We confirmed the safer profile of optiLAIV in Stat1^-/- mice (highly susceptible to viral infections) by showing no signs of morbidity compared to a 50% mortality rate from LAIV. OptiLAIV could expand the applications of the current LAIV and help mitigate the burden of IAV in susceptible populations.

Evaluation of transplacental transfer of mRNA vaccine products and functional antibodies during pregnancy and infancy

Studies are needed to evaluate the safety and effectiveness of mRNA SARS-CoV-2 vaccination during pregnancy, and the levels of protection provided to their newborns through placental transfer of antibodies. Here, we evaluate the transplacental transfer of mRNA vaccine products and functional anti-SARS-CoV-2 antibodies during pregnancy and early infancy in a cohort of 20 individuals vaccinated during late pregnancy. We find no evidence of mRNA vaccine products in maternal blood, placenta tissue, or cord blood at delivery. However, we find time-dependent efficient transfer of IgG and neutralizing antibodies to the neonate that persists during early infancy. Additionally, using phage immunoprecipitation sequencing, we find a vaccine-specific signature of SARS-CoV-2 Spike protein epitope binding that is transplacentally transferred during pregnancy. Timing of vaccination during pregnancy is critical to ensure transplacental transfer of protective antibodies during early infancy.

Risk of seroconversion and seroreversion of antibodies to Chlamydia trachomatis pgp3 in a longitudinal cohort of children in a low trachoma prevalence district in Tanzania

Background

Serologic testing for chlamydial antibodies is one potential tool for trachoma monitoring. Understanding the dynamics of seroconversion and seroreversion in low endemic districts is critical for determining the value of using serology.

Methodology/Principal findings

We surveyed a random sample of 2536 children aged 1–9 years in Kongwa, Tanzania, over three years; 1719 (67.8%) participants had all three follow-ups. Surveys assessed trachomatous inflammation—follicular (TF), Chlamydia trachomatis infection, and anti-pgp3 antibodies. Mass drug administration occurred immediately after the first and second follow-up surveys. The cohort was classified into trajectories of change in serostatus, and risk factors were evaluated for seroconversion and seroreversion. We found that 86.2% of seropositives remained seropositive throughout the study, whereas 12.1% seroreverted. Seroreverters were younger (Odds Ratio [OR] = 0.88 for every one-year increase in age, 95% CI = 0.79–0.99). 84.5% of seronegatives remained seronegative, and 13.0% seroconverted. Seroconverters were also younger (OR = 0.92, 95% CI = 0.87–0.98). Seroconversion and seroreversion were not explained by indeterminate values for the intensity of antibody response. Less than 1% of the cohort had unstable changes in serostatus, mostly explained by values in the indeterminate range. TF and infection in the cohort declined over time, while seropositivity increased from 31.5% to 36.4%.

Conclusions/Significance

Antibody status is relatively stable over time. Both seroconversion and seroreversion occurred over the three years in this low endemic district, especially in younger children. Modeling seroreversion is important for accurate determination of seroconversion. The use of serology as a monitoring tool should target the younger aged children as they will most likely capture recent changes in serostatus.

Trachoma, the leading infectious cause of blindness worldwide, is a chronic conjunctivitis caused by repeated infection with Chlamydia trachomatis. As more endemic regions approach the trachoma elimination goal, it becomes critical to identify tools that can be used for monitoring the potential resurgence or re-emergence of trachoma. Serologic testing for chlamydial antibodies is one potential tool. Understanding the risk of seroconversion and seroreversion in children in low endemic districts is critical for determining the value of serology as a monitoring tool. We followed a cohort of children in the formerly trachoma endemic Kongwa district in Tanzania over three years. We demonstrated the relative stability of antibody status with 85–86% of the children retaining their baseline serostatus. We also documented an overall seroconversion rate of 13% and a seroreversion rate of 12%. We found younger ages to be a risk factor for both seroconversion and seroreversion. Our study provides necessary new evidence for the slow rate of overall change in seroprevalence over three years and highlights the potential use of the younger aged children for sero-monitoring of trachoma as they are more likely to reflect the dynamic interplay of true seroconversion and seroreversion. Furthermore, using only cross-sectional serostatus to estimate seroconversion may result in an underestimate if seroreversion rates are not included in the estimation.

Rubella

Rubella is an acute illness caused by rubella virus and characterised by fever and rash. Although rubella is a clinically mild illness, primary rubella virus infection in early pregnancy can result in congenital rubella syndrome, which has serious medical and public health consequences. WHO estimates that approximately 100 000 congenital rubella syndrome cases occur per year. Rubella virus is transmitted through respiratory droplets and direct contact. 25-50% of people infected with rubella virus are asymptomatic. Clinical disease often results in mild, self-limited illness characterised by fever, a generalised erythematous maculopapular rash, and lymphadenopathy. Complications include arthralgia, arthritis, thrombocytopenic purpura, and encephalitis. Common presenting signs and symptoms of congenital rubella syndrome include cataracts, sensorineural hearing impairment, congenital heart disease, jaundice, purpura, hepatosplenomegaly, and microcephaly. Rubella and congenital rubella syndrome can be prevented by rubella-containing vaccines, which are commonly administered in combination with measles vaccine. Although global rubella vaccine coverage reached only 70% in 2020 global rubella eradiation remains an ambitious but achievable goal.

Long-Term Varicella Zoster Virus Immunity in Paediatric Liver Transplant Patients Can Be Achieved by Booster Vaccinations—A Single-Centre, Retrospective, Observational Analysis

Varicella is one of the most common vaccine-preventable infections after paediatric solid organ transplantation; thus, vaccination offers simple and cheap protection. However, children with liver disease often progress to liver transplantation (LT) before they reach the recommended vaccination age. As a live vaccine, varicella zoster virus (VZV) vaccination after transplantation is controversial; however, many case series demonstrate that vaccination may be safe and effective in paediatric liver transplant recipients. Only limited data exists describing long-term vaccination response in such immunocompromised patients. We investigated retrospectively vaccination response in paediatric patients before and after transplantation and describe long-term immunity over ten years, including the influence of booster-vaccinations. In this retrospective, single-centre study, 458 LT recipients were analysed between September 2004 and June 2021. Of these, 53 were re-transplantations. Patients with no available vaccination records and with a history of post-transplant lymphoproliferative disease, after hematopoietic stem cell transplantation and clinical chickenpox were excluded from this analysis (n = 198). In total, data on 207 children with a median annual follow-up of 6.2 years was available: 95 patients (45.9%) were unvaccinated prior to LT. Compared to healthy children, the response to vaccination, measured by seroconversion, is weaker in children with liver disease: almost 70% after one vaccination and 93% after two vaccinations. One year after transplantation, the mean titres and the number of children with protective antibody levels (VZV IgG ≥ 50 IU/L) decreased from 77.5% to 41.3%. Neither diagnosis, gender, nor age were predictors of vaccination response. Booster-vaccination was recommended for children after seroreversion using annual titre measurements and led to a significant increase in mean titre and number of protected children. Response to vaccination shows no difference from monotherapy with a calcineurin inhibitor to intensified immunosuppression by adding prednisolone or mycophenolate mofetil. Children with liver disease show weaker seroconversion rates to VZV vaccination compared to healthy children. Therefore, VZV-naïve children should receive basic immunization with two vaccine doses as well as those vaccinated only once before transplantation. An average of 2–3 vaccine doses are required in order to achieve a long-term seroconversion and protective antibody levels in 95% of children.

Evaluation of transplacental transfer of mRNA vaccine products and functional antibodies during pregnancy and early infancy

Studies are needed to evaluate the safety and effectiveness of mRNA SARS-CoV-2 vaccination during pregnancy, and the levels of protection provided to their newborns through placental transfer of antibodies. We evaluated the transplacental transfer of mRNA vaccine products and functional anti-SARS-CoV-2 antibodies during pregnancy and early infancy in a cohort of 20 individuals vaccinated during pregnancy. We found no evidence of mRNA vaccine products in maternal blood, placenta tissue, or cord blood at delivery. However, we found time-dependent efficient transfer of IgG and neutralizing antibodies to the neonate that persisted during early infancy. Additionally, using phage immunoprecipitation sequencing, we found a vaccine-specific signature of SARS-CoV-2 Spike protein epitope binding that is transplacentally transferred during pregnancy. In conclusion, products of mRNA vaccines are not transferred to the fetus during pregnancy, however timing of vaccination during pregnancy is critical to ensure transplacental transfer of protective antibodies during early infancy.

Relative Ratios of Human Seasonal Coronavirus Antibodies Predict the Efficiency of Cross-Neutralization of SARS-CoV-2 Spike Binding to ACE2

BACKGROUND

Antibodies raised against human seasonal coronaviruses (sCoVs), which are responsible for the common cold, are known to cross-react with SARS-CoV-2 antigens. This prompts questions about their protective role against SARS-CoV-2 infections and COVID-19 severity. However, the relationship between sCoVs exposure and SARS-CoV-2 correlates of protection are not clearly identified.

METHODS

We performed a cross-sectional analysis of cross-reactivity and cross-neutralization to SARS-CoV-2 antigens (S-RBD, S-trimer, N) using pre-pandemic sera from four different groups: pediatrics and adolescents, individuals 21 to 70 years of age, older than 70 years of age, and individuals living with HCV or HIV. Data was then further analysed using machine learning to identify predictive patterns of neutralization based on sCoVs serology.

FINDINGS

Antibody cross-reactivity to SARS-CoV-2 antigens varied between 1.6% and 15.3% depending on the cohort and the isotype-antigen pair analyzed. We also show a range of neutralizing activity (0-45%) with median inhibition ranging from 17.6 % to 23.3 % in serum that interferes with SARS-CoV-2 spike attachment to ACE2 independently of age group. While the abundance of sCoV antibodies did not directly correlate with neutralization, we show that neutralizing activity is rather dependent on relative ratios of IgGs in sera directed to all four sCoV spike proteins. More specifically, we identified antibodies to NL63 and OC43 as being the most important predictors of neutralization.

INTERPRETATION

Our data support the concept that exposure to sCoVs triggers antibody responses that influence the efficiency of SARS-CoV-2 spike binding to ACE2, which may potentially impact COVID-19 disease severity through other latent variables.

FUNDING

This study was supported by a grant by the CIHR (VR2 -172722) and by a grant supplement by the CITF, and by a NRC Collaborative R&D Initiative Grant (PR031-1).

Selective functional antibody transfer into the breastmilk after SARS-CoV-2 infection

Antibody transfer via breastmilk represents an evolutionary strategy to boost immunity in early life. Although severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-specific antibodies have been observed in the breastmilk, the functional quality of these antibodies remains unclear. Here, we apply systems serology to characterize SARS-CoV-2-specific antibodies in maternal serum and breastmilk to compare the functional characteristics of antibodies in these fluids. Distinct SARS-CoV-2-specific antibody responses are observed in the serum and breastmilk of lactating individuals previously infected with SARS-CoV-2, with a more dominant transfer of immunoglobulin A (IgA) and IgM into breastmilk. Although IgGs are present in breastmilk, they are functionally attenuated. We observe preferential transfer of antibodies capable of eliciting neutrophil phagocytosis and neutralization compared to other functions, pointing to selective transfer of certain functional antibodies to breastmilk. These data highlight the preferential transfer of SARS-CoV-2-specific IgA and IgM to breastmilk, accompanied by select IgG subpopulations, positioned to create a non-pathologic but protective barrier against coronavirus disease 2019 (COVID-19).

A M2 protein-based universal influenza vaccine containing Advax-SM adjuvant provides newborn protection via maternal or neonatal immunization

BACKGROUND

Despite newborns being at increased risk of serious influenza infection, influenza vaccines are currently not recommended for use in infants under 6 months of age. We therefore sought to evaluate the protective efficacy in mice of an M2-based influenza vaccine (CapM2e) formulated with Advax-SM adjuvant. Vaccine protection was assessed via both passive maternal immunization and direct neonatal immunization.

METHODS

For maternal transfer studies, female mice were immunized 1 week before and after mating. Blood was collected from both mother and offspring during weaning and pups were challenged when they reached 3 weeks of age with lethal doses of H1N1 and homologous reassortment influenza strain H3N2 with conserved M2. For direct immunization studies, newborns were immunized at 1 and 3 weeks of age and blood was collected prior to challenge at 4 weeks of age.

RESULTS

Maternal immunization with CapM2e + Advax-SM vaccine induced high maternal M2e antibody levels that were passively transferred to their offspring and provided them with protection against both H1N1 and H3N2 influenza strains when challenged at 3 weeks of age. When used for direct immunization of neonatal mice, CapM2e + Advax-SM vaccine similarly induced high serum M2e antibody levels and protected against H1N1 and H3N2 influenza challenges with protection associated with inhibition of virus replication with a significant reduction in lung virus load in immunized pups.

CONCLUSION

CapM2e + Advax-SM vaccine could be useful for protecting newborns against diverse influenza A strains, with opportunities to achieve protection by passive maternal immunization or active neonatal immunization. This data supports further development of this promising M2e-based vaccine candidate.

Measuring association among censored antibody titer data

Censoring due to a limit of detection or limit of quantification happens quite often in many medical studies. Conventional approaches to deal with censoring when analyzing these data include, for example, the substitution method and the complete case (CC) analysis. More recently, maximum likelihood estimation (MLE) has been increasingly used. While the CC analysis and the substitution method usually lead to biased estimates, the MLE approach appears to perform well in many situations. This article proposes an MLE approach to estimate the association between two measurements in the presence of censoring in one or both quantities. The central idea is to use a copula function to join the marginal distributions of the two measurements. In various simulation studies, we show that our approach outperforms existing conventional methods (CC and substitution analyses). In addition, rank‐based measures of global association such as Kendall's tau or Spearman's rho can be studied, hence, attention is not only confined to Pearson's product‐moment correlation coefficient capturing solely linear association. We have shown in our simulations that our approach is robust to misspecification of the copula function or marginal distributions given a small association. Furthermore, we propose a straightforward MLE method to fit a (multiple) linear regression model in the presence of censoring in a covariate or both the covariate and the response. Given the marginal distribution of the censored covariate, our method outperforms conventional approaches. We also compare and discuss the performance of our method with multiple imputation and missing indicator model approaches.

Comprehensive analysis of COVID-19 during pregnancy

The COVID-19 pandemic resulting from the emergence of the coronavirus SARS-CoV-2 remains a major global health concern. Pregnant individuals are more likely to develop severe COVID-19 and a number of pregnancy complications have been observed in COVID-19 patients. To date, little is known about the impact of COVID-19 on pregnancy. In this review, we examine key aspects of pregnancy that may be impacted by COVID-19 and summarize the current literature on SARS-CoV-2 infection of the placenta and in utero vertical transmission. Furthermore, we highlight recent studies exploring the role of the maternal antibody response to SARS-CoV-2 during pregnancy and the passive transfer of maternal antibodies from mothers with COVID-19 to fetus.

Limited Neonatal Carbohydrate-Specific Antibody Repertoire Consecutive to Partial Prenatal Transfer of Maternal Antibodies

Despite the prominence of carbohydrate-specific antibodies in human sera, data on their emergence and antigen specificities are limited. Whereas maternal IgG are transferred prenatally to the fetal circulation, IgM present in cord blood originate from fetal B lymphocytes. Considering the limited exposure of the fetus to foreign antigens, we assessed the repertoire of carbohydrate-specific antibodies in human cord blood and matched maternal blood samples using glycan arrays. Carbohydrate-specific IgM was absent in cord blood, whereas low cord blood IgG reactivity to glycans was detectable. Comparing IgG reactivities of matched pairs, we observed a general lack of correlation in the antigen specificity of IgG from cord blood and maternal blood due to a selective exclusion of most carbohydrate-specific IgG from maternofetal transfer. Given the importance of intestinal bacteria in inducing carbohydrate-specific antibodies, we analyzed global antibody specificities toward commensal bacteria. Similar IgG reactivities to specific Bacteroides species were detected in matched cord and maternal blood samples, thus pointing to an efficient maternal transfer of anti-microbial IgG. Due to the observed selectivity in maternofetal IgG transfer, the lack of fetal antibodies to carbohydrate epitopes is only partially compensated by maternal IgG, thus resulting in a weak response to carbohydrate antigens in neonates.

Tick-borne encephalitis virus (TBEV) infection in pregnancy: Absence of virus transmission to the fetuses despite severe maternal disease - A case study

Tick-borne encephalitis (TBE) is an emerging infectious disease in large parts of Europe and Asia. Whereas other members of the Flaviviridae family can harm fetal development, there are only very few reports on TBE virus (TBEV) infections during pregnancy. Thus, the implications for fetal health remain largely unknown. In this study, we present detailed pre- and postnatal health assessment of three children in the context of severe maternal TBEV infection during pregnancy. Following acute TBEV infection of the mothers, intrauterine growth and development of all children were assessed by repetitive prenatal ultrasound. Postnatal examinations included clinical and virological analyses over a follow-up period of 18 months. Prenatally, no signs of intrauterine growth restrictions were observed. All neonates were delivered at term. Umbilical cord blood of the newborns tested negative for TBEV RNA. Virus-specific IgG antibodies were positive at birth but negative at 9 and 11 months of age. Importantly, IgM antibodies remained negative throughout the period of observation. Taken together, these clinical and virological data strongly suggest that fetal TBEV infection did not occur, despite severe manifestations in the mothers.

Mother-to-Child Transfer of Reactivated Varicella-Zoster Virus DNA and Varicella-Zoster IgG in Pregnancy

Stress-induced subclinical reactivation of varicella-zoster virus (VZV) has been studied previously. However, subclinical reactivation of VZV induced by the stress of pregnancy has not been investigated. The objective was to study varicella DNA and varicella antibody levels in mothers and their newborn babies. VZV immunoglobulin G (IgG) levels in 350 mother-newborn dyads were studied using indirect enzyme-linked immunosorbent assay testing. A subset of 73 dyads was selected, DNA was isolated from the serum samples, and quantitative polymerase chain reaction (qPCR) was performed. Nearly 15% (14.6%) mothers tested were positive for varicella antibodies (>100 mIU/dL) and 16% were borderline (<100 and >50 mIU/dL). Approximately 16.9% of the babies were positive, and 18% were in borderline. Among those tested for VZV-DNA, 70% of mothers with low VZ-IgG (<100 mIU/dL) and 11.32% of those with high VZ-IgG (>100 mIU/dL) were positive for DNA. Among the newborns, 60% of those with low VZ-IgG and 15% of those with high VZ-IgG were positive for DNA. Mothers who have had VZV infection in the past can transmit VZV DNA to their babies.

Dynamics of the Humoral Immune Response to a Prime-Boost Ebola Vaccine: Quantification and Sources of Variation

The Ebola vaccine based on Ad26.ZEBOV/MVA-BN-Filo prime-boost regimens is being evaluated in multiple clinical trials. The long-term immune response to the vaccine is unknown, including factors associated with the response and variability around the response. We analyzed data from three phase 1 trials performed by the EBOVAC1 Consortium in four countries: the United Kingdom, Kenya, Tanzania, and Uganda. Participants were randomized into four groups based on the interval between prime and boost immunizations (28 or 56 days) and the sequence in which Ad26.ZEBOV and MVA-BN-Filo were administered. Consecutive enzyme-linked immunosorbent assay (ELISA) measurements of the IgG binding antibody concentrations against the Kikwit glycoprotein (GP) were available for 177 participants to assess the humoral immune response up to 1 year postprime. Using a mathematical model for the dynamics of the humoral response, from 7 days after the boost immunization up to 1 year after the prime immunization, we estimated the durability of the antibody response and the influence of different factors on the dynamics of the humoral response. Ordinary differential equations (ODEs) described the dynamics of antibody response and two populations of antibody-secreting cells (ASCs), short-lived (SL) and long-lived (LL). Parameters of the ODEs were estimated using a population approach. We estimated that half of the LL ASCs could persist for at least 5 years. The vaccine regimen significantly affected the SL ASCs and the antibody peak but not the long-term response. The LL ASC compartment dynamics differed significantly by geographic regions analyzed, with a higher long-term antibody persistence in European subjects. These differences could not be explained by the observed differences in cellular immune response.IMPORTANCE With no available licensed vaccines or therapies, the West African Ebola virus disease epidemic of 2014 to 2016 caused 11,310 deaths. Following this outbreak, the development of vaccines has been accelerated. Combining different vector-based vaccines as heterologous regimens could induce a durable immune response, assessed through antibody concentrations. Based on data from phase 1 trials in East Africa and Europe, the dynamics of the humoral immune response from 7 days after the boost immunization onwards were modeled to estimate the durability of the response and understand its variability. Antibody production is maintained by a population of long-lived cells. Estimation suggests that half of these cells can persist for at least 5 years in humans. Differences in prime-boost vaccine regimens affect only the short-term immune response. Geographical differences in long-lived cell dynamics were inferred, with higher long-term antibody concentrations induced in European participants.

Immunity to varicella zoster virus among pregnant women in the Norwegian Mother and Child Cohort Study

Introduction

Infection with varicella zoster virus (VZV) in pregnancy may lead to serious outcomes both for the mother and the newborn. Targeted screening and vaccination of non-immune women during reproductive age could prevent varicella infection in pregnancy. Currently, no universal varicella screening of pregnant women is implemented in Norway, but serological testing in pregnancy is recommended in particular situations. We examined seroprevalence of VZV in a national pregnancy cohort in order to help assess a need for VZV screening of women during reproductive age.

Methods

We determined the susceptibility to VZV and the reliability of self-reported history of VZV infection in the Norwegian obstetric population by using a random sample of 1,184 pregnant women from the Norwegian Mother and Child Cohort study (MoBa). The MoBa study included approximately 95,200 pregnant women in Norway between 1998 and 2009. Blood samples taken at gestational week 17–18 were analysed using a commercial enzyme immunoassay for specific IgG antibodies to Varicella-Zoster virus. Second sample taken at birth was tested if the first sample result was negative or equivocal.

Results

Of the 1,184 pregnant women, 98.6% (n = 1,167) were seropositive, 0.83% (n = 10) remained seronegative, and four women (0.34%) seroconverted during their pregnancy. No significant associations were found between serological status and women’s age at birth, gestational age, women’s country of birth and year of child’s birth. One woman reported prior history of varicella, whereas 143 (12.1%) women reported a household exposure to childhood diseases with fever and rash, of which 25 reported exposure to varicella, of which all were seropositive.

Conclusions

The findings support antenatal screening recommendations in Norway advising testing for VZV in pregnant women with unknown immunity to VZV. Further studies are however needed to better identify target groups for screening and vaccination.

Measles, mumps, rubella (vaccine) and varicella vaccines in pediatric liver transplant: An initial analysis of post-transplant immunity

Varicella and measles infection represents a significant source of morbidity and mortality for pediatric LT recipients. We evaluated the prevalence and correlates of post-transplant immunity in pediatric LT recipients previously immunized against measles (n = 72) and varicella (n = 67). Sixteen of seventy-two (22%) patients were measles non-immune, and 42/67 (63%) were varicella non-immune after LT. Median time from LT to titers for measles and varicella was 4.0 and 3.3 years, respectively. In the measles cohort, non-immune patients received fewer pretransplant vaccine doses (P = 0.026) and were younger at both time of vaccination (P = 0.006) and LT (P = 0.004) compared with immune patients. Upon multivariable analysis, weight > 10 kg at LT (OR 5.91, 95% CI 1.27-27.41) and technical variant graft (OR 0.07, 95% CI 0.01-0.37) were independently, significantly associated with measles immunity. In the varicella cohort, non-immune patients received fewer pretransplant vaccine doses (P = 0.028), were younger at transplant (P = 0.022), and had less time lapse between their last vaccine and transplant (P = 0.012) compared with immune patients. Upon multivariate analysis, time > 1 year from last vaccine to LT was independently, significantly associated with varicella immunity (OR 3.78, CI 1.30-11.01). This study demonstrates that non-immunity to measles and varicella is a prevalent problem after liver transplantation in children and identifies 3 unique risk factors for non-immunity in this high-risk population.

Why Should We Advocate Maternal Immunization?

Maternal vaccination provides a method for protecting the pregnant woman, fetus and neonate during a period when there is increased susceptibility to infectious diseases. A dynamic state of immune tolerance during pregnancy and the need to develop adaptive memory to a new foreign antigen-rich environment lead to windows of vulnerability to infection for the mother and neonate, respectively. Passive transfer of humoral immunity through the placenta and breast milk from the mother can bridge the gap in immunity for the neonate. Studies on boosting this natural process of antibody transfer have led to the recommendation for administering inactivated influenza, diphtheria, tetanus toxoid and acellular pertussis vaccines during pregnancy. Several new maternal vaccine candidates are on the horizon.

Epidemiological and clinical characteristics and the approach to infant chickenpox in primary care

Chickenpox is not common in the first year of life (infant varicella) and there is a lack of data on its presentation, especially in primary care. A year-long observational study (July 2015-2016) carried out by a research network of primary care pediatricians throughout Spain.Two hundred and sixty-four pediatricians gathered data from 358 cases of clinically diagnosed chickenpox in infants. The illness was considered mild in 78% of infants < 7 months compared to 65% in those aged 7 to 12 months (p = 0.0144). Fever (46%) was present in 35% of children ≤ 6 months compared to 55% in older children (p = 0.0005). The number of skin lesions was > 50 in 35% of children ≤ 6 months old compared to 47% in > 7 months (p = 0.0273). From the 2% of hospitalized children 86% were younger than 7 months. Oral antiviral treatment was given in 33% of cases ≤ 6 months compared to 18% in older patients (p = 0.0023). Doubts about administering the chickenpox vaccine at a later date were expressed by 18% of pediatricians.Conclusion: Chickenpox is considered benign, having a mild effect on most infants. There is less clinical effect in infants ≤ 6 months although this age group is hospitalized more and is prescribed more antiviral treatment. There are doubts among pediatricians about the subsequent need for vaccination. What is Known: • Chickenpox is uncommon and of uncertain evolution in the first year of life • Hospital admissions for chickenpox are more frequent in the first year of life What is New: • The course of chickenpox in the first year of life is mild, especially in infants younger than 7 months despite the fact they are hospitalized more and are treated more frequently with antivirals. Antivirals are prescribed to 1 in 4 children with chickenpox under 12 months of age. • Almost 50% of pediatricians recommend a subsequent vaccination against chickenpox especially if it occurs in the first 6 months of life.

The repertoire of maternal anti-viral antibodies in human newborns

All circulating immunoglobulin G (IgG) antibodies in human newborns are of maternal origin¹ and transferred across the placenta to provide passive immunity until newborn IgG production takes over 15 weeks after birth². However, maternal IgG can also negatively interfere with newborn vaccine responses³. The concentration of IgG increases sharply during the third trimester of gestation and children delivered extremely preterm are believed to largely lack this passive immunity^1,2,4. Antibodies to individual viruses have been reported^5-12, but the global repertoire of maternal IgG, its variation in children, and the epitopes targeted are poorly understood. Here, we assess antibodies against 93,904 epitopes from 206 viruses in 32 preterm and 46 term mother-child dyads. We find that extremely preterm children receive comparable repertoires of IgG as term children, albeit at lower absolute concentrations and consequent shorter half-life. Neutralization of the clinically important respiratory syncytial virus (RS-virus) was also comparable until three months of age. These findings have implications for understanding infectious disease susceptibility, vaccine development, and vaccine scheduling in newborn children.

Assignment of cytomegalovirus infection status in infants awaiting solid organ transplant: Viral detection methods as adjuncts to serology

Assignment of CMV infection status in infants awaiting SOT is challenging as passive maternal antibody can lead to false-positive serology. Since 2000, our protocol has recommended sending throat and urine samples for CMV viral detection, culture, or NAAT, for CMV-seropositive infants <18 months awaiting SOT. We reviewed pretransplant CMV serology for 152 infants and, for CMV seropositives, examined relationships between CMV IgG OD values, age, and CMV viral detection to explore time to clearance of maternal CMV IgG and evaluate viral detection in assignment of pretransplant CMV infection status. The proportion of CMV-seropositive infants decreased from 52% in infants 0-6 months of age to 28% in those 12-18 months. Among CMV-seropositive infants, median OD was significantly higher in the 6- to 12- and 12- to 18-month groups compared to the 0- to 6-month group. Distribution of OD by age group suggested that maternal antibody cleared before 12 months. Of 59 eligible CMV-seropositive infants, 49 (83%) had CMV viral detection studies and 18 of 49 (36.7%) had detectable CMV: 9 of 30 (30.0%) infants 0-6 months, 7 of 15 (46.7%) infants 6-12 months, and 2 of 4 (50.0%) infants 12-18 months. CMV viral detection studies are useful to confirm positive CMV infection status in CMV-seropositive infants awaiting SOT. Maternal CMV IgG likely clears before 12 months.

Recent advances in vertebrate and invertebrate transgenerational immunity in the light of ecology and evolution

Parental experience with parasites and pathogens can lead to increased offspring resistance to infection, through a process known as transgenerational immune priming (TGIP). Broadly defined, TGIP occurs across a wide range of taxa, and can be viewed as a type of phenotypic plasticity, with hosts responding to the pressures of relevant local infection risk by altering their offspring's immune defenses. There are ever increasing examples of both invertebrate and vertebrate TGIP, which go beyond classical examples of maternal antibody transfer. Here we critically summarize the current evidence for TGIP in both invertebrates and vertebrates. Mechanisms underlying TGIP remain elusive in many systems, but while it is unlikely that they are conserved across the range of organisms with TGIP, recent insight into epigenetic modulation may challenge this view. We place TGIP into a framework of evolutionary ecology, discussing costs and relevant environmental variation. We highlight how the ecology of species or populations should affect if, where, when, and how TGIP is realized. We propose that the field can progress by incorporating evolutionary ecology focused designs to the study of the so far well chronicled, but mostly descriptive TGIP, and how rapidly developing -omic methods can be employed to further understand TGIP across taxa.

Australian rubella serosurvey 2012-2013: On track for elimination?

BACKGROUND

The World Health Organization has targeted rubella virus for elimination regionally. Australia was one of the first countries to implement a nationally funded rubella immunisation program, in 1971, and conducts regular national rubella serosurveillance studies. We aimed to estimate the seroprevalence of rubella-specific IgG antibody in the Australian population by age and sex in 2012-2013, to compare the results with three previous serosurveys conducted in 1996-1999, 2002 and 2007 and to estimate the effective reproduction numbers (R_n).

METHODS

This study used 2729 serum and plasma specimens, randomly selected from a specimen bank collected in 2012-2013 across Australia. Age groups included in the sample ranged from 1 to 49 years. Sera were tested for rubella-specific IgG-antibody using the Enzygnost anti-rubella IgG enzyme immunoassay and classified as positive, negative or equivocal according to rubella-specific IgG concentrations of >7 IU/ml, <3 IU/ml and 3-7 IU/ml, respectively.

RESULTS

The overall proportions seropositive, seronegative and equivocal for rubella-specific IgG were 92.1% (95% CI, 91.0-93.2), 6.7% (95% CI, 5.7-7.7) and 1.2% (95% CI, 0.8-1.6), respectively. The proportion of males seropositive was significantly lower than females in the 30-34 (83.1% vs. 96.8%, p = 0.003), 35-39 (86.1% vs. 96.3%, p = 0.02) and 40-44 (86.1% vs. 95.7%, p = 0.03) year age groups. R_n for rubella in 2012-2013 was estimated to be 0.33 (95% CI 0.28-0.39).

DISCUSSION

The 2012-2013 national serosurvey showed levels of rubella-specific IgG seropositivity in the Australian population are relatively high with no evidence of decrease compared to previous serosurveys conducted in 1996-1999, 2002 and 2007. The lower proportion of seropositive males aged 30-44 years likely reflects the initial immunisation program targeting females only. To our knowledge this study represents the longest period of serosurveillance following introduction of a nationally funded rubella immunisation program. The lack of evidence of decreasing rubella-specific IgG seropositivity is therefore reassuring for Australia and other countries with longstanding high vaccine coverage.

Longitudinal change in the serology of antibodies to Chlamydia trachomatis pgp3 in children residing in a trachoma area

A serologic test for antibodies to chlamydial antigen pgp3 may be a useful tool for trachoma surveillance. However, little is known about the stability of antibody status over time, or factors associated with seroreversion/conversion. A cohort of 2,111 children ages 1-9 years in Tanzania were followed for one year in the absence of mass azithromycin. At baseline and follow-up, they were evaluated for trachoma, chlamydial infection, and antibodies to chlamydial antigen pgp3. At baseline, 31% of children were seropositive for pgp3 antibodies and 6.4% seroreverted to negative over one year. Of those seronegative, 9.8% seroconverted over the year. The seroreverters had lower baseline mean fluorescence intensity (MFI-BG) values compared to the seropositives who remained positive (Odds Ratio = 0.04 for every unit increase in log₁₀MFI-BG, 95% CI = 0.02-0.09), and were more likely to live in communities with trachoma <5% (p < 0.008). While seroconversion was expected, seroreversion was unexpected. The low seroprevalence rate reported from low endemic areas may be due to seroreversion as well as lack of exposure.

Effect of Prepregnancy Pertussis Vaccination in Young Infants

Background

Maternal antibodies to pertussis can hamper infant immune responses to pertussis vaccines. The effect a maternal tetanus, diphtheria, acellular pertussis (Tdap) vaccine booster between 2 consecutive pregnancies is investigated.

Methods

A prospective study was conducted in Belgium during 2008-2014 on the kinetics of maternal pertussis antibodies in unvaccinated women and their infants (group A; 86 mother-infant pairs) and in siblings born after the women received Tdap vaccine (group B; 58 mother-infant pairs). Levels of antibody to pertussis toxin, antibody to filamentous hemagglutinin, and antibody to pertactin were measured in maternal blood before and after vaccination and at both deliveries, in cord blood from both siblings, and in infants before and after they received a priming series of acellular pertussis containing vaccines.

Results

Levels of pertussis antibodies in all group B siblings at birth were significantly higher than those in their siblings at birth, even as the interval since maternal vaccination increased. Blunting of the infant pertussis vaccine response was detected in group B siblings. We estimated the maximum interval between repeat Tdap vaccine doses in adult women that would yield a beneficial effect for the consecutive infant.

Conclusions

Prepregnancy Tdap vaccination significantly increases maternal antibody concentrations in consecutive infants. However, similar to the effect of Tdap vaccination during pregnancy, immune responses of later-born infants born to mothers who received a prepregnancy immunization, are blunted.

Estimation of the burden of varicella in Europe before the introduction of universal childhood immunization

BACKGROUND

Varicella is generally considered a mild disease. Disease burden is not well known and country-level estimation is challenging. As varicella disease is not notifiable, notification criteria and rates vary between countries. In general, existing surveillance systems do not capture cases that do not seek medical care, and most are affected by underreporting and underascertainment. We aimed to estimate the overall varicella disease burden in Europe to provide critical information to support decision-making regarding varicella vaccination.

METHODS

We conducted a systematic literature review to identify all available epidemiological data on varicella IgG antibody seroprevalence, primary care and hospitalisation incidence, and mortality. We then developed methods to estimate age-specific varicella incidence and annual number of cases by different levels of severity (cases in the community, health care seekers in primary care and hospitals, and deaths) for all countries belonging to the European Medicines Agency (EMA) region and Switzerland.

RESULTS

In the absence of universal varicella immunization, the burden of varicella would be substantial with a total of 5.5 million (95% CI: 4.7-6.4) varicella cases occurring annually across Europe. Variation exists between countries but overall the majority of cases (3 million; 95% CI: 2.7-3.3) would occur in children <5 years. Annually, 3-3.9 million patients would consult a primary care physician, 18,200-23,500 patients would be hospitalised, and 80 varicella-related deaths would occur (95% CI: 19-822).

CONCLUSIONS

Varicella disease burden is substantial. Most cases occur in children <5 years old but adults require hospitalisation more often and are at higher risk of death. This information should be considered when planning and evaluating varicella control strategies. A better understanding of the driving factors of country-specific differences in varicella transmission and health care utilization is needed. Improving and standardizing varicella surveillance in Europe, as initiated by the European Centre for Disease Prevention and Control (ECDC), is important to improve data quality to facilitate inter-country comparison.

Pertussis vaccination in pregnancy: State of the art

Pertussis vaccination in pregnancy has been introduced by several national advisory bodies, mostly in industrialized countries, as a means to protect young infants from disease by high titers of maternal antibodies. Most recommendations derive from epidemiological needs, but many knowledge gaps remained after implementation. This report aims to overview the solved and unsolved aspects of prenatal vaccination with a pertussis containing vaccine.

Seroprevalences of Specific IgG Antibodies to Measles, Mumps, and Rubella in Korean Infants

In this study, the seroprevalences of measles, mumps, and rubella antibodies in infants were determined to assess the immunization strategy and control measures for these infectious diseases. Serum samples from infants < 1 year of age and their mothers were collected to measure the concentrations of specific IgG antibodies to measles, mumps, and rubella by enzyme-linked immunosorbent assay. For selected infant serum samples, measles-specific neutralizing antibody levels were determined by using the plaque reduction neutralization test. The sera from 295 of infants and 80 of their mothers were analyzed. No infants had past measles, mumps, or rubella infections. Almost all infants < 2 months of age were positive for measles and rubella IgG antibodies. However, seroprevalence of measles and rubella antibodies decreased with age, and measles IgG and rubella IgG were barely detectable after 4 months of age. The seroprevalence of mumps antibodies was lower than that of measles and rubella antibodies in infants ≤ 4 months old, and mumps IgG was barely detectable after 2 months of age. The seropositivity of measles-specific neutralizing antibody was 63.6% in infants aged 2 months and undetectable in infants ≥ 6 months old. Because the seropositivity rates of measles, mumps, and rubella antibodies were low after the first few months of age in Korean infants, active immunization with vaccines is strongly recommended for infants aged 6-11 months when measles is epidemic. Timely administration of the first dose of measles-mumps-rubella vaccine at 12 months of age should be encouraged in non-epidemic situations.

Inferring rubella outbreak risk from seroprevalence data in Belgium

Rubella is usually a mild disease for which infections often pass by unnoticed. In approximately 50% of the cases, there are no or only few clinical symptoms. However, rubella contracted during early pregnancy could lead to spontaneous abortion, to central nervous system defects, or to one of a range of other serious and debilitating conditions in a newborn such as the congenital rubella syndrome. Before the introduction of mass vaccination, rubella was a common childhood infection occurring all over the world. However, since the introduction of rubella antigen-containing vaccines, the incidence of rubella has declined dramatically in high-income countries. Recent large-scale mumps outbreaks, one of the components in the combined measles-mumps-rubella vaccine, occurring in countries throughout Europe with high vaccination coverage, provide evidence of pathogen-specific waning of vaccine-induced immunity and primary vaccine failure. In addition, recent measles outbreaks affecting populations with suboptimal vaccination coverages stress the importance of maintaining high vaccination coverages. In this paper, we focus on the assessment of rubella outbreak risk using a previously developed method to identify geographic regions of high outbreak potential. The methodology relies on 2006 rubella seroprevalence data and vaccination coverage data from Belgium and information on primary and secondary vaccine failure obtained from extensive literature reviews. We estimated the rubella outbreak risk in Belgium to be low, however maintaining high levels of immunisation and surveillance are of utmost importance to avoid future outbreaks.

JC virus infection is acquired very early in life: evidence from a longitudinal serological study

JC virus (JCV) is a widespread member of the Polyomaviridae family. Following primary infection, which occurs asymptomatically during childhood, JCV establishes latency in the host. JCV seroprevalence can reach 80 % in healthy adults, but the age of viral exposure has not been yet characterized. This study was conducted to define JCV seroprevalence in Italian infants and to estimate the date of primary infection. A JCV viral protein 1 (VP1)-GST fusion protein was used in conjunction with a homemade indirect enzyme-linked immunosorbent assay (ELISA) to test for the presence of IgG antibodies to JCV in 981 serum samples collected from 644 Italian infants of different ages (1 day to 3 years old) and in 102 breast milk samples. IgM antibody presence was also evaluated in longitudinally collected samples from 17 selected children. JCV antibody prevalence and normalized optical density (nOD) were calculated. For the longitudinal analysis, generalized estimating equation techniques and spline functions were used to estimate the possible non-linear effects of time on antibody production kinetics. JCV IgG was detected in 71.8 % of the sera. Prevalence increased over time from 46.1 % (1 month old) to 80.7 % (12 months old), 85.9 % (24 months old), and 85.5 % (36 months old). As determined by nOD, the longitudinal analysis of serum IgG amounts in children of this study (ages 1 day to 3 years old) illustrated IgG kinetic changes with statistically significant trends (p = 0.001). One-month-old children were largely negative for JCV IgM (82.4 %), and 58.8 % of children produced JCV IgM within the second and sixth months of life. JCV IgG was detected in 27.3 % of breast milk samples. JCV primary infection likely occurs before 6 months of age, and a sizeable percentage of Italian infants will become JCV seropositive within 2 years of age. This study can be used to determine the optimal age for potential future JCV vaccination in infants.

Systematic Review of Measles and Rubella Serology Studies

Serological tests provide information about individual immunity from historical infection or immunization. Cross-sectional serological studies provide data about the age- and sex-specific immunity levels for individuals in the studied population, and these data can provide a point of comparison for the results of transmission models. In the context of developing an integrated model for measles and rubella transmission, we reviewed the existing measles and rubella literature to identify the results of national serological studies that provided cross-sectional estimates of population immunity at the time of data collection. We systematically searched PubMed, the Science Citation Index, and references we identified from relevant articles published in English. We extracted serological data for comparison to transmission model outputs. For rubella, serological studies of women of child-bearing age provide information about the potential risks of infants born with congenital rubella syndrome. Serological studies also document the loss of maternal antibodies, which occurs at different rates for the different viruses and according to the nature of the induced immunity (i.e., infection or vaccine). The serological evidence remains limited for some areas, with studies from developed countries representing a disproportionate part of the evidence. The collection and review of serological evidence can help program managers identify immunity gaps in the population, which may help them better understand the characteristics of individuals within their populations who may participate in transmission and manage risks.

Persistence and Half-lives of Anti-measles and Anti-rubella Antibodies in Japanese Hospital Workers: A Longitudinal Study

Objective Antibody testing for endemic viruses in healthcare workers is used as an index of immunoprotection in Japan. However, it remains unclear how these antibody titers chronologically change and how they should be interpreted. Methods We retrospectively collected two sets of antibody titers to measles and rubella, measured in 2013 and within the preceding 5 years, in adult hospital workers by an enzyme-linked immunoassay and calculated in international units. Subjects infected with, or vaccinated against, these viruses over this period were eliminated. Seropositivities and geometric mean titers were analyzed. Decay rates and half-lives of antibodies were calculated using a mixed-effect model according to the subjects' ages and antibody titers. Results We analyzed 469 subjects for measles and 439 for rubella. Comparison with previous data revealed a mean measurement interval of 1,026 days between the previous and present tests, with seropositivity rates of 98.0% (previous) vs. 99.3% (present) for measles; 974 days and 90.7% vs. 94.9%, respectively, for rubella. For measles and rubella, 97.4% and 86.1%, respectively, of previously seropositive subjects remained positive in the present test. The geometric mean titers in the present and previous tests were 924.3 IU/mL and 853.2 IU/mL (measles) and 46.23 IU/mL and 40.78 IU/mL (rubella), respectively. In the mixed-effect model, measles and rubella antibody titers showed an increasing trend with age. Conclusion Seropositivities against measles and rubella can remain high for more than 5 years. Among adult hospital workers in Japan, the antibody titers against measles and rubella have a sufficient lifetime persistence.

Acquisition and Longevity of Antibodies to Plasmodium vivax Preerythrocytic Antigens in Western Thailand

Plasmodium vivax is now the dominant Plasmodium species causing malaria in Thailand, yet little is known about naturally acquired immune responses to this parasite in this low-transmission region. The preerythrocytic stage of the P. vivax life cycle is considered an excellent target for a malaria vaccine, and in this study, we assessed the stability of the seropositivity and the magnitude of IgG responses to three different preerythrocytic P. vivax proteins in two groups of adults from a region of western Thailand where malaria is endemic. These individuals were enrolled in a yearlong cohort study, which comprised one group that remained P. vivax free (by quantitative PCR [qPCR] detection, n = 31) and another that experienced two or more blood-stage P. vivax infections during the year of follow up (n = 31). Despite overall low levels of seropositivity, IgG positivity and magnitude were long-lived over the 1-year period in the absence of qPCR-detectable blood-stage P. vivax infections. In contrast, in the adults with two or more P. vivax infections during the year, IgG positivity was maintained, but the magnitude of the response to P. vivax circumsporozoite protein 210 (CSP210) decreased over time. These findings demonstrate that long-term humoral immunity can develop in low-transmission regions.

MATHEMATICAL MODELLING OF VARICELLA SPREAD IN SLOVAKIA

AIM

Varicella is a highly contagious disease. In Slovakia, 15,000-30,000 cases are reported annually. However, vaccination against varicella is not widely used in Slovakia. The aim of this paper is to predict the influence of vaccination administrated in different ages on the disease occurrence in different age groups.

METHODS

Deterministic, age-stratified SIR (susceptible-infected-recovered) model with stable population was used for prediction of varicella spread in Slovakia.

RESULTS

Vaccination of a group designated as 0 influences the proportion of susceptible and infected persons in all age groups, vaccination of 10 years old ones affects only the proportion of susceptible and infected individuals older than 10 years.

CONCLUSION

The increase of vaccination coverage should have a positive impact on the incidence of varicella in Slovakia. In case of vaccination coverage of 0 group in the range of 30-75%, it is necessary to pay attention to the protection of older children and adults.

Pertussis vaccination during pregnancy in Belgium: Results of a prospective controlled cohort study

Vaccination during pregnancy has been recommended in some countries as a means to protect young infants from severe infection. Nevertheless, many aspects are still unknown and possible blunting of the infant's immune responses by maternal antibodies, is one of the concerns with maternal vaccination. We report the first prospective controlled cohort study in women and infants on the effects of using Boostrix(®), a combined tetanus, diphtheria and acellular pertussis vaccine, during pregnancy. The primary aim was to measure the influence of this booster dose on the titer and duration of the presence of maternal antibodies in the infants and assess possible interference with infant immune responses. In a controlled cohort study, 57 pregnant women were vaccinated with Tdap vaccine (Tetanus Diphtheria acellular Pertussis, Boostrix, GSK Biologicals), at a mean gestational age of 28.6 weeks. A control group of pregnant women (N=42) received no vaccine. Antibody geometric mean concentrations (GMCs) against tetanus (TT), diphtheria (DT), pertussis toxin (PT), filamentous haemagglutinin (FHA) and pertactin (Prn) were measured with commercial ELISA tests in samples taken preceding maternal vaccination and one month afterwards, at delivery and from the cord blood, and in infants before and 1 month after the primary series of 3 pertussis containing hexavalent vaccines. Infants born to vaccinated women had significantly higher GMC at birth and during the first 2 months of life for all vaccine antigens compared to the offspring of unvaccinated women, thereby closing the susceptibility gap for pertussis in infants. However, blunting was noticed for infant diphtheria and pertussis toxin vaccine responses (p<0.001) in the infants from vaccinated women after the primary vaccination schedule (weeks 8,12 and 16). Since pertussis vaccination has been recommended during pregnancy already, the results of this study support that recommendation and provide additional scientific evidence to document possible interference by maternal antibodies.

Pertussis vaccination during pregnancy in Vietnam: Results of a randomized controlled trial Pertussis vaccination during pregnancy

A pertussis vaccination during pregnancy has recently been adopted in several countries to indirectly protect young infants. This study assessed the effect of adding a pertussis component to the tetanus vaccination, in the pregnancy immunization program in Vietnam. A randomized controlled trial was performed. Pregnant women received either a Tdap (tetanus, diphtheria acellular pertussis) vaccine or a tetanus only vaccine between 19 and 35 weeks' gestational age. Immunoglobulin G (IgG) against tetanus (TT), diphtheria (DT), pertussis toxin (PT), filamentous hemaglutinin (FHA) and pertactin (Prn) were measured using commercial ELISA tests, at baseline, 1 month after maternal vaccination, at delivery, and in infants from cord blood and before and after the primary series (EPI: month 2-3-4) of a pertussis containing vaccine. Significantly higher geometric mean concentrations (GMC) were observed for all 3 measured pertussis antigens in the offspring of the Tdap group, up to 2 months of age. One month after completion of the primary infant vaccination schedule, anti-Prn GMC, but not anti-PT and anti-FHA GMCs, was significantly (p=0.006) higher in the control group. Maternal antibodies induced by vaccination during pregnancy close the susceptibility gap for pertussis in young infants. Limited interference with the infant vaccine responses was observed. Whether this interference effect disappears with the administration of a fourth vaccine dose is further studied.

Immunization of pregnant women: Future of early infant protection

Children in early infancy do not mount effective antibody responses to many vaccines against commons infectious pathogens, which results in a window of increased susceptibility or severity infections. In addition, vaccine-preventable infections are among the leading causes of morbidity in pregnant women. Immunization during pregnancy can generate maternal immune protection as well as elicit the production and transfer of antibodies cross the placenta and via breastfeeding to provide early infant protection. Several successful vaccines are now recommended to all pregnant women worldwide. However, significant gaps exist in our understanding of the efficacy and safety of other vaccines and in women with conditions associated with increased susceptible to high-risk pregnancies. Public acceptance of maternal immunization remained to be improved. Broader success of maternal immunization will rely on the integration of advances in basic science in vaccine design and evaluation and carefully planned clinical trials that are inclusive to pregnant women.

Susceptibility to measles, mumps, and rubella in 5-year-old children in Flanders, Belgium

The second dose of an MMR vaccine is a catch up for persons who did not receive the first dose or for primary vaccine failures. Catch up doses can be scheduled according to convenience into the program of the country. The second MMR dose is often administered at the age of 5 years, before school entry. Some countries chose to implement the second dose at the age of 10-13 years, as is the case for Belgium. The here presented long-term follow-up of a cohort of children, set up originally to analyze maternal antibodies against vaccine preventable diseases, offers a unique opportunity to evaluate ad interim the current long-interval MMR vaccination schedule in Belgium. After 1 MMR dose at 12 months of age, rubella immunity is almost intact at 5 years of age (94.5 % is seropositive), measles seropositivity scores 86.8 %, and mumps 32 %, measured with ELISA. A seroneutralization (SN) test for mumps antibodies reveals much higher seropositivity rates (88 %). Using a regression model on the log (IgG) titer for all antigens, no influence was found from any of the studied variables, except for girls who had a significantly higher rubella IgG titer (p=0.002) compared to boys.

CONCLUSION

The data show considerable susceptibility to mumps and measles in 5-year-old children, confirming a previously conducted seroprevalence study (2006). Both advantages and disadvantages of shortening or enlarging the vaccine schedule are discussed.

Determining the persistence of maternally acquired antibodies to hepatitis A and varicella zoster during the first 2 years of life in Turkey

Vaccination should be timed to take into account the potential interference of maternal antibodies. The purpose of this study was to determine the persistence of maternally acquired antibodies to hepatitis A and varicella zoster in a group of healthy infants between 6 and 24 months of age. These infants were divided into four groups according to the age at the time of follow-up visits. The study group consisted of infants who were brought to the 6-month follow-up visit (group 1, n=100), 12-month follow-up visit (group 2, n=99), 18-month follow-up visit (group 3, n=59), and 24-month follow-up visit (group 4, n=59). Hepatitis A, varicella IgG, and IgM antibodies were analyzed qualitatively. Hepatitis A IgG seropositivity was determined as 71 % in group 1, 41.4 % in group 2, 0 % in group 3, and 8.5 % in group 4 (p<0.001). Varicella IgG seropositivity was found to be 5 % in group 1, 4 % in group 2, 4 % in group 3, and 1 % in group 4 (p>0.05).

CONCLUSION

We found that maternal hepatitis A antibodies in children disappear between 12 and 18 months, whereas maternal varicella antibodies substantially diminish following the sixth month. Therefore, the vaccination timing should be based on factors such as the interference of maternal antibodies, disease susceptibility period, and immune maturation.