Immunity against measles in populations of women and infants in Poland

Measles susceptibility in maternal-infant dyads-Bamako, Mali

Measles is endemic in Africa; measles mortality is highest among infants. Infant measles antibody titer at birth is related to maternal immune status. Older mothers are likelier to have had measles infection, which provides higher antibody titers than vaccine-induced immunity. We investigated the relationship between maternal age and measles susceptibility in mother-infant pairs in Mali through six months of infancy. We measured serum measles antibodies in 340 mother-infant pairs by plaque reduction neutralization test (PRNT) and calculated the proportion of mothers with protective titers (>120 mIU/mL) at delivery and the proportion of infants with protective titers at birth, and at three and six months of age. We explored associations between maternal age and measles antibodies in mothers and infants at the timepoints noted. Ten percent of Malian newborns were susceptible to measles; by six months nearly all were. Maternal and infant antibody titers were highly correlated. At delivery, 11% of mothers and 10% of newborns were susceptible to measles. By three and six months, infant susceptibility increased to 72% and 98%, respectively. Infants born to younger mothers were most susceptible at birth and three months. Time to susceptibility was 6.6 weeks in infants born to mothers with measles titer >120-<430 mIU/mL versus 15.4 weeks when mothers had titers ≥430 mIU/mL. Maternal and newborn seroprotective status were positively correlated. Improved strategies are needed to protect susceptible infants from measles infection and death. Increasing measles immunization coverage in vaccine eligible populations, including nonimmune reproductive-aged women and older children should be considered.

Measles, rubella, mumps and Toxoplasma gondii antibodies in saliva of vaccinated students of schools and universities in São Paulo City, Brazil

Introduction

Vaccines are well-established public health interventions with major impact on the prevalence of infectious diseases, but outbreaks are occurring frequently due to primary and secondary failures, despite high coverage. Surveillance of efficacy and duration of induced immunity is a difficult task as it requires invasive blood sampling in children and teenagers. Saliva can be an acceptable alternative source of IgG to assess vaccine efficacy and toxoplasmosis incidence. We investigated IgG response for measles, mumps, rubella, and T. gondii in saliva samples of vaccinated young people.

Methods

Saliva was collected from 249 public schools students from São Paulo, Brazil, aged 7 to 13 years old, during an interactive exhibition on hygiene. We used S. aureus protein A solid phase capture assay for IgG reactive to biotinylated purified proteins. Paired saliva and serum (47) were tested from young adults with serum evidence of T. gondii infection and from negative children less than 12 month old for standardization. Reproducibility was greater than 98% and sensitivity and specificity of the saliva assays were greater than 95%, as well as the concordance of paired saliva and serum samples.

Results

Saliva from high school students showed a prevalence of 8.5% (95% CI: 5.0–11.9%) for anti T. gondii IgG; 96.8% (94.6–99%) of anti-measles IgG; 59.1% (53–65%) of anti-rubella IgG, and 57.5% (51.3–63.6%) of anti-mumps IgG.

Discussion

The prevalence of antibodies against mumps and rubella after 6–8 years of vaccination was lower than against measles among students. The findings of this study demonstrate the feasibility of saliva sampling for follow-up of vaccine immune status in teenagers. This useful approach allows for IgG detection for vaccine control or epidemiological studies.

Decreasing Seroprevalence of Measles Antibodies after Vaccination - Possible Gap in Measles Protection in Adults in the Czech Republic

Aims

In recent years, Europe has recorded an increase in the number of measles outbreaks despite the implementation of vaccination into the National Immunization Programs. The Czech Republic introduced vaccination against measles into National Immunization Program in 1969. The aim of this study was to determine seroprevalence of IgG antibodies against measles in adults.

Methods

Our study was designed as a prospective, multicenter cohort study. Samples of blood were taken from adults aged 18 years and over. Specific IgG antibodies were determined by ELISA method.

Results

A number of 1911 sera samples were obtained. The total seropositivity reached 83.3%, 14.3% of the results were negative and 2.4% were borderline. When comparing the individual age groups, the highest antibody seropositivity (> 96%) was detected in persons aged 50 years and over who were naturally infected in pre-vaccine era. The lowest seropositivity was recorded in the age groups 30–39 years (61.5%), 40–49 years (77.5%) and 18–29 years (81.1%).

Conclusions

A long term high rate of seropositivity persists after natural measles infection. By contrast, it decreases over time after vaccination. Similarly, the concentrations of antibodies in persons with measles history persist for a longer time at a higher level than in vaccinated persons. Our results indicate possible gap in measles protection in adults born after implementation of vaccination into the National Immunization Programs. There are two probable reasons, decrease of measles antibody seropositivity in time after vaccination in setting of limited natural booster and one-dose vaccination schedule used in the first years after implementation.

The epidemiological and serological characteristics of measles in Dongguan, China, 2005-2014

This study examined the epidemiological and serological characteristics of measles in Dongguan, China. From 2005 to 2014, a total of 8,224 measles cases were reported in Dongguan, 33.5% of which were aged <1 y and 30.6% >14 y. From 2005 to 2014, the proportion of the <1 y measles cases increased year by year from 24.3% to 47.9%. Of the cases aged ≥8 months (n = 6,768 cases), only 11.6% had been immunized with at least one dose of measles vaccine. Of the 2,213 cases who had never been immunized with measles vaccine, immigrants accounted for 82.4%. 52.4% of the measles cases were diagnosed with pneumonia, and 12 cases died from respiratory failure. Seroprevalence rate in women and their newborns was 86.0% and 82.5%, respectively. Measurement of serum measles antibody levels for infants aged less than 8 months indicated that seroprevalence rate dramatically declined from 97.3% at birth to 9.3% and 13.2% at 6- and 7- month old. The existence of a sufficient pool of unvaccinated people (especially immigrants) and decreased level of passively transferred measles antibodies in infants from vaccinated mothers contributed to the sustained transmission observed in Dongguan. In addition to high routine vaccination coverage, new strategies and innovations for measles vaccination are needed to eliminate measles.

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.

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.

Measles vaccine coverage estimates in an outbreak three years after the nation-wide campaign in China: implications for measles elimination, 2013

Background

China is approaching measles elimination, but indigenous measles still circulates. County L in China has reported measles-containing vaccine (MCV) coverage rates >95% since 2000. Despite high reported coverage, a large measles outbreak occurred among young children in L County. We measured MCV coverage using 5 different methods during an investigation on this outbreak and compared our estimates with reported rates.

Methods

Reported coverage rates are determined by aggregating clinic-based data across the county: doses administered in each clinic divided by the number of children registered in each clinic. Our methods estimated coverage for the 2010–2012 birth cohort, and were (1) administrative method: doses administered in clinics divided by the birth cohort recorded in the Statistical Year Book, (2) house-to-house convenience-sample survey of children living near cases, (3) vaccination clinic records review, (4) determination of a convenience sample of measles outbreak cases’ vaccination statuses and using the field vaccine efficacy outbreak equation to estimate population coverage, and (5) a seroprevalence survey using a convenience sample of residual blood samples from hospitals.

Results

The measles outbreak totaled 215 cases, representing an incidence of 195.8 per million population. Our estimated MCV coverage rates were: (1) administrative method: 84.1%-87.0% for MCV1 and 80.3%-90.0% for MCV2, (2) in-house survey: 83.3% of 9–17 month children received MCV1, and 74.5% of 24–47 month children received MCV2, (3) clinic record review: 85.5% of 9–17 month children received MCV1, and 73.2% of 24–59 month children received MCV2, (4) field VE method: 83.6% of 9–47 month children received one or more MCV doses, and (5) serology: seropositive rates were <80% in the 12–17 and 18–23 month age cohorts.

Conclusions

Compared with reported coverage >95%, our 5 coverage assessments all showed substantially lower coverage. China should evaluate guidelines for reporting vaccination coverage and identify feasible improvements to the assessment methods.

Lower transplacental antibody transport for measles, mumps, rubella and varicella zoster in very preterm infants

BACKGROUND

Maternal antibodies, transported over the placenta during pregnancy, contribute to the protection of infants from infectious diseases during the first months of life. In term infants, this protection does not last until the first recommended measles-mumps-rubella vaccination at 14 months in the Netherlands, while these viruses still circulate. The aim of the study was to investigate the antibody concentration against measles, mumps, rubella and varicella (MMRV) in mothers and preterm infants or healthy term infants at birth.

METHODS

Antibody concentrations specific for MMRV were measured in cord blood samples from preterm (gestational age <32 weeks and/or birth weight <1500 g) and term infants, and matched maternal serum samples, using a fluorescent bead-based multiplex immune-assay.

RESULTS

Due to lower placental transfer ratios of antibodies against MMRV in 96 preterm infants (range 0.75-0.87) compared to 42 term infants (range 1.39-1.65), the preterm infants showed 1.7-2.5 times lower geometric mean concentrations at birth compared to term infants. Maternal antibody concentration is the most important determinant of infant antibody concentration against MMRV.

CONCLUSIONS

Preterm infants benefit to a lesser extent from maternal antibodies against measles, mumps, rubella and varicella than term infants, posing them even earlier at risk for infectious diseases caused by these still circulating viruses.

Age-related changes in serological susceptibility patterns to measles: results from a seroepidemiological study in Dongguan, China

The present study was performed to determine the seroprevalence of IgG measles antibodies in Dongguan residents (irrespective of vaccination status), to analyze the changes in age-related serological susceptibility patterns. A total of 1960 residents aged 0-60 years and 315 mother-infant pairs were studied. Serum IgG antibodies against measles virus were measured by ELISA. The overall seroprevalence was 93.4% in the general population in Dongguan, China. In subgroups aged 1-29 years who were likely vaccinated, there was a declining trend of seropositivity with age from 98.6% at 1-4 years to 85.7% at 20-29 years (P<0.0001). Seroprevalence were near or>95% in the older population (30-39 years and ≥ 40 years) who had not been immunized against measles. Age and sex were independent factors associated with seropositivity. Seroprevalence in pregnant women and their newborns was 87.0% and 84.1%, respectively. Our results suggest that the waning vaccine-induced immunity may be the main cause of increased serological susceptibility in young adults and young infants. An additional vaccination strategy that targets young adults is important for elimination of measles.

Timeliness vaccination of measles containing vaccine and barriers to vaccination among migrant children in East China

Background

The reported coverage rates of first and second doses of measles containing vaccine (MCV) are almost 95% in China, while measles cases are constantly being reported. This study evaluated the vaccine coverage, timeliness, and barriers to immunization of MCV₁ and MCV₂ in children aged from 8–48 months.

Methods

We assessed 718 children aged 8–48 months, of which 499 children aged 18–48 months in September 2011. Face to face interviews were administered with children’s mothers to estimate MCV₁ and MCV₂ coverage rate, its timeliness and barriers to vaccine uptake.

Results

The coverage rates were 76.9% for MCV₁ and 44.7% for MCV₂ in average. Only 47.5% of surveyed children received the MCV₁ timely, which postpone vaccination by up to one month beyond the stipulated age of 8 months. Even if coverage thus improves with time, postponed vaccination adds to the pool of unprotected children in the population. Being unaware of the necessity for vaccination and its schedule, misunderstanding of side-effect of vaccine, and child being sick during the recommended vaccination period were significant preventive factors for both MCV₁ and MCV₂ vaccination. Having multiple children, mother’s education level, household income and children with working mothers were significantly associated with delayed or missing MCV₁ immunization.

Conclusions

To avoid future outbreaks, it is crucial to attain high coverage levels by timely vaccination, thus, accurate information should be delivered and a systematic approach should be targeted to high-risk groups.

Duration of maternally derived antibody against measles: a seroepidemiological study of infants aged under 8 months in Qinghai, China

To estimate the sero-prevalence of protective maternal measles antibodies among young infants and examine patterns of waning immunity in one of the poorest provinces in China, infants aged under 8 months and their mothers were randomly selected by multi-stage probabilistic sampling and blood samples were collected. Measles-specific IgG antibodies were measured in all serum samples by enzyme-linked immunosorbent assay. We determined measles-specific antibody titres for 477 pairs of infants and their mothers. After excluding 44 sub-clinical measles infection in infants, the measles antibody titres were ≧1:200, ≧1:800, and ≧1:3200 in 79.2%, 46.9%, and 17.8% of the 433 infants, respectively. The proportion of infants with titre ≧1:800 declined with age from 90.2% in newborns to 45.5% and 14.9% in the fourth and eighth month, respectively. Among the 433 mothers, measles antibody titres were ≧1:800 in 94.0%. Multivariate regression analysis showed that residence, mother's antibody levels and infant's age were significantly associated with infants' having a measles antibody titre ≧1:800. The relatively rapid decay of protective antibody in infants suggests that an earlier administration of the first dose of measles vaccination should be considered in China and a high quality interventional study is needed to decide the optimal schedule of measles immunization.

Early waning of maternal measles antibodies: why immunization programs should be adapted over time

Primary protection against measles in the first months of life is provided by transferred maternal antibodies. Since the introduction of the measles vaccine, changes in epidemiology have had major effects on the transmission of protective antibodies. The majority of women of childbearing age are now vaccinated and transfer fewer antibodies than naturally immune mothers, conferring shorter protection to their offspring. This article reveals an early loss of maternal antibodies in infants of vaccinated mothers but also in infants of naturally immune women. This increasing susceptibility window between loss of maternal antibodies and vaccination should be taken into account for a timely administration of the first dose of measles vaccine, particularly in the current context of re-emerging measles in Europe. Additional programs are needed to improve vaccination coverage within the global population and to reduce the spread of measles.

Scheduling of measles vaccination in low-income countries: projections of a dynamic model

Large-scale vaccination campaigns (SIAs) and improved routine immunization (RI) have greatly reduced measles incidence in low-income countries. However, the interval between SIAs required to maintain these gains over the long term is not clear. We developed a dynamic model of measles transmission to assess measles vaccination strategies in Cambodia, Ghana, India, Morocco, Nigeria, and Uganda. We projected measles cases from 2008 to 2050 under (a) holding SIAs every 2, 4, 6, or 8 years, (b) improvements in first dose routine measles vaccine (MCV1) coverage of 0%, 1%, 3% annually, and (c) introducing MCV2 once MCV1 coverage reaches 70%, 80%, 90%. If MCV1 continues improving, then India and Nigeria could hold SIAs every 4 years without significant probability of large outbreaks, and the other countries every 6-8 years. If RI remains stagnant, India and Nigeria should hold SIAs every 2 years, and the other countries every 4-6 years.

Kinetics of decline of maternal measles virus-neutralizing antibodies in sera of infants in France in 2006

The optimal age for measles vaccination is an important health issue, since maternal antibodies may neutralize the vaccine antigen before a specific immune response develops, while delaying vaccination may increase the risk of complicated diseases in infants. However, measles vaccination impacts the duration of protection afforded by transplacental transfer of maternal antibodies: vaccination-induced maternal antibodies disappear faster than disease-induced antibodies. In order to maintain protection against measles in infants, it is important to monitor the dynamics of this phenomenon in vaccinated populations. To assess the current situation in France, a multicenter, prospective seroepidemiological study was conducted in seven French hospitals between October 2005 and January 2007. Maternal measles antibody concentrations from 348 infants 0 to 15 months old were measured using the plaque reduction neutralization assay. Geometric mean concentrations and the percentage of infants with maternal measles antibody concentrations above the protection threshold (>or=120 mIU/ml) were assessed according to age. Results show that after more than 20 years of routine measles vaccination in France, maternal measles-neutralizing antibodies decrease dramatically in French infants by 6 months of age, from 1,740 mIU/ml for infants 0 to 1 month old to 223 mIU/ml for infants 5 to 6 months old, and that 90% of infants are not protected against measles after 6 months of age. Infant protection against measles could be optimized both by increasing herd immunity through an increased vaccine coverage and by lowering the age of routine vaccination from 12 to 9 months.

Passive transmission and persistence of naturally acquired or vaccine-induced maternal antibodies against measles in newborns

This paper reviews literature on passively transferred maternal antibodies against measles in infants. The amount and decay of these antibodies can be a result of changing patterns in society: increasing cohorts of women are vaccinated against measles instead of having naturally acquired immunity, the age of first childbirth is increasing and young adults are less exposed to natural boosters. The concentration and persistence of maternal antibodies differ in infants of women vaccinated against measles versus infants of naturally immune women. The date for commencing universal measles vaccination should take into account the presence of these antibodies since they can hamper the immunological response to vaccination. Each country should therefore consider adapting the timing of vaccination in relation to its measles sero-epidemiological situation. The possibility of priming the immune system with an early vaccine dose and boosting later on offers opportunities for vaccination at very young age.

Distribution of serum measles-neutralizing antibodies according to age in women of childbearing age in France in 2005-2006: impact of routine immunization

Measles antibody titers were measured in 210 French women. Ninety-four percent had protective values (>120 mIU/mL). Geometric mean titers were significantly different (P < 0.001) between women born before and after 1983, when measles vaccination was recommended (731 and 1358 mIU/mL, respectively). geometric mean titers in 4 age cohorts decreased significantly (P < 0.001) with increasing birth year. These data may help identify the appropriate age for infant vaccination.

Current status of measles in Japan: molecular and seroepidemiological studies

On account of the measles vaccination campaign, with vaccinations carried out on the first birthdays of children, the number of reported cases of measles was reduced to 545 in 2005, which is the lowest so far in Japan. We conducted a molecular epidemiological study of measles virus to determine the circulating measles virus genotypes in Japan since 1984. Different genotypes, C1, D3, D5, and H1, were the major strains isolated in outbreaks in 1984, 1987-1988, 1991-1993, and 2000, respectively. When measles was in the control phase, a sporadic outbreak was reported, but the causative virus was found to be of imported measles virus lineage. We also conducted a seroepidemiological study to investigate the persistence of vaccine-acquired immunity in Himeji City, Japan. Before 1990, vaccine coverage was 84.5% and it increased gradually, to 88.5% in 1991-1995, 92.7% in 1996-2000, and 94.6% after 2000. Measles outbreaks were observed annually before 1978 and in 1980, 1981, 1984, 1990, and 1996; there were no measles cases after 1997 in Himeji City. In 1994-1998, a serological study of 795 sera showed that measles neutralization test (NT) antibodies were sufficiently preserved, even 12 years after the first-dose immunization. In 1999-2003, 26 (3.7%) of 695 sera were negative for NT. The positive rate for measles NT decreased to approximately 90% as the elapsed time after the first-dose immunization increased to 6 or 7 years. The immunity obtained after receiving measles vaccine decays by 6-7 years after the first dose when the measles was controlled. A two-dose schedule of measles vaccine was implemented in Japan in 2006; we should continue molecular and serological surveillance.

Modelling the effect of a booster vaccination on disease epidemiology

Despite the effectiveness of vaccines in dramatically decreasing the number of new infectious cases and severity of illnesses, imperfect vaccines may not completely prevent infection. This is because the immunity afforded by these vaccines is not complete and may wane with time, leading to resurgence and epidemic outbreaks notwithstanding high levels of primary vaccination. To prevent an endemic spread of disease, and achieve eradication, several countries have introduced booster vaccination programs. The question of whether this strategy could eventually provide the conditions for global eradication is addressed here by developing a seasonally-forced mathematical model. The analysis of the model provides the threshold condition for disease control in terms of four major parameters: coverage of the primary vaccine; efficacy of the vaccine; waning rate; and the rate of booster administration. The results show that if the vaccine provides only temporary immunity, then the infection typically cannot be eradicated by a single vaccination episode. Furthermore, having a booster program does not necessarily guarantee the control of a disease, though the level of epidemicity may be reduced. In addition, these findings strongly suggest that the high coverage of primary vaccination remains crucial to the success of a booster strategy. Simulations using estimated parameters for measles illustrate model predictions.

Timeliness of MMR vaccination—influence on vaccination coverage

Over the last seven years, and especially in 2001, a declining coverage for MMR vaccination in 2-year-olds has been noted in Sweden. By recording actual date of vaccination in a cohort of almost 4,000 children in a county in central Sweden, we found that parents' decision to postpone vaccination by up to 1.5 years beyond the stipulated age of 18 months accounted for about half the reported drop in 2001. Even if coverage thus improves with time, postponed vaccination adds to the pool of unprotected children in the population. The design of the current national surveillance system overestimates coverage at 2 years and fails to record delayed vaccination. To avoid future outbreaks that can appear around imported cases of measles it is crucial to attain high coverage levels by timely vaccination.