Measles, polio and tetanus toxoid antibody levels in Gambian children aged 3 to 4 years following routine vaccination

Effect of early measles vaccination on long-term protection: A systematic review

BACKGROUND

In North America, the first dose of a measles-containing vaccine (MCV1) is administered at ≥12 months of age. However, MCV1 may be given to infants <12 months living in highly endemic areas or traveling to these areas. Although an early dose of MCV1 leads to immediate protection, it remains unclear how this impacts long-term immunity.

METHODS

This systematic review and meta-analysis evaluates the impact of MCV1 given at <12 months vs. ≥12 months of age on long-term immunogenicity and vaccine effectiveness, with long-term defined as at least one-year post-vaccination. PubMed, EMBASE, Global Health, Web of Science and Scopus were searched on October 31st, 2019. Studies were included if they included a cohort of infants vaccinated <12 months of age and evaluated long-term immunogenicity, vaccine efficacy, or effectiveness.

RESULTS

A total of 51 texts were identified: 23 reported outcomes related to vaccine effectiveness and 30 to immunogenicity. Infants vaccinated with MCV1 < 12 months of age showed an overall higher risk of measles compared to ≥12 months of age (RR = 3.16, 95% CI: 2.00, 5.01; OR = 2.46, 95% CI: 1.40, 4.32). Risk of measles decreased with increasing age at first vaccination, with those vaccinated with one dose ≥15 months at a lesser risk compared to 12-14 months or <12 months. Measles seroconversion and seropositivity was not affected by age at first vaccination, but antibody levels were significantly lower in the MCV1 < 12-month group (MD = -0.40, 95% CI: -0.71, -0.09).

CONCLUSION

Long-term measles seroconversion and seropositivity did not appear to be affected by age at MCV1, while vaccine effectiveness decreased with younger age. There was not enough evidence to look at the effect of age at MCV1 on immune blunting.

Serological Surveys for complementing assessments of vaccination coverage in sub-Saharan Africa: A systematic review

Background: Serosurveys of biomarkers of infection/vaccination are widely used for evaluating vaccine-induced immunity and monitoring the effectiveness of immunisation programmes in developed countries. In sub-Saharan Africa (sSA) where vaccination coverage (VC) estimates are often incomplete, inaccurate and overestimate effective population immunity, the use of serosurveys is limited. Methods: We conducted a review of the use of serosurveys to assess/complement assessments of VC in sSA by searching electronic databases (PubMed, Embase, Web of Science, Popline, Ovid and Africa Wide Information) for English language articles published from 1st January 1940 to 31st January 2017. We also searched the references of retrieved articles. SSA was defined as all of Africa excluding the countries in North Africa. We included only articles that measured VC and assessed the quality of these studies using the Newcastle-Ottawa Scale. Results: We found 1056 unique records, reviewed 20 eligible studies of which just 12 met our inclusion criteria. These 12 studies were serosurveys of measles, tetanus, polio and yellow fever. Antibodies induced by natural infection confounded serological test results and there was significant discordance between vaccination history and the presence of antibodies in all except for tetanus vaccine. No study looked at Hepatitis B. Conclusions: Serosurveys for tetanus or tetanus containing vaccines may be directly useful for ascertainment of vaccination exposure or reliably complement current survey methods that measure VC. Given the limited experience in using serosurveys for this purpose in sSA, well-designed serosurveys of tetanus and possibly hepatitis B are required to further validate/evaluate their performance.

Synthesis of Evidence to Characterize National Measles and Rubella Exposure and Immunization Histories

Population immunity depends on the dynamic levels of immunization coverage that countries achieve over time and any transmission of viruses that occur within the population that induce immunity. In the context of developing a dynamic transmission model for measles and rubella to support analyses of future immunization policy options, we assessed the model inputs required to reproduce past behavior and to provide some confidence about model performance at the national level. We reviewed the data available from the World Health Organization (WHO) and existing measles and rubella literature for evidence of historical reported routine and supplemental immunization activities and reported cases and outbreaks. We constructed model input profiles for 180 WHO member states and three other areas to support disease transmission model development and calibration. The profiles demonstrate the significant variability in immunization strategies used historically by regions and member states and the epidemiological implications of these historical choices. The profiles provide a historical perspective on measles and rubella immunization globally at the national level, and they may help immunization program managers identify existing immunity and/or knowledge gaps.

Measuring coverage in MNCH: design, implementation, and interpretation challenges associated with tracking vaccination coverage using household surveys

Vaccination coverage is an important public health indicator that is measured using administrative reports and/or surveys. The measurement of vaccination coverage in low- and middle-income countries using surveys is susceptible to numerous challenges. These challenges include selection bias and information bias, which cannot be solved by increasing the sample size, and the precision of the coverage estimate, which is determined by the survey sample size and sampling method. Selection bias can result from an inaccurate sampling frame or inappropriate field procedures and, since populations likely to be missed in a vaccination coverage survey are also likely to be missed by vaccination teams, most often inflates coverage estimates. Importantly, the large multi-purpose household surveys that are often used to measure vaccination coverage have invested substantial effort to reduce selection bias. Information bias occurs when a child's vaccination status is misclassified due to mistakes on his or her vaccination record, in data transcription, in the way survey questions are presented, or in the guardian's recall of vaccination for children without a written record. There has been substantial reliance on the guardian's recall in recent surveys, and, worryingly, information bias may become more likely in the future as immunization schedules become more complex and variable. Finally, some surveys assess immunity directly using serological assays. Sero-surveys are important for assessing public health risk, but currently are unable to validate coverage estimates directly. To improve vaccination coverage estimates based on surveys, we recommend that recording tools and practices should be improved and that surveys should incorporate best practices for design, implementation, and analysis.

EPI vaccines-induced antibody prevalence in 8-9 year-olds in The Gambia

OBJECTIVES

We evaluated antibody prevalence to measles, polio 1 and 3, and tetanus toxoid antibodies in 8-9 year-old children in The Gambia within the framework of the Gambia Hepatitis Intervention Study (GHIS), a large vaccine trial aimed at evaluating vaccine efficacy against hepatitis B virus (HBV) infection, chronic carriage and primary liver cancer in a high risk population. The results of the present survey were compared with a previous survey performed with the same objectives and same methodology but in different children at 3-4 years of age.

METHODS

Four clusters of 200 children each were sampled as representative of the whole country. Children would have received BCG, diphtheria-pertussis-tetanus vaccine (DPT), poliovirus vaccine (OPV), measles and yellow fever immunization. The measles haemoagglutination inhibition test (HAI) was used to detect measles antibody. Antibodies to polioviruses 1 and 3 were tested using the standard polio neutralization assay described in the EPI manual (WHO 1990). An enzyme-linked immuno-sorbent assay (ELISA) was used to measure tetanus toxoid antibodies.

RESULTS

A high proportion of children were fully vaccinated in both age groups. Measles antibody concentrations were < or =1 : 8 in 8.2% of 8-9 year-old vaccinated children. In the previous survey of 3-4 year-old children this was 11.3%. In the present survey, GMC was lower than in the 3-4 year-old children; 88% of 3-4 year-olds and 89% of 8-9 year-olds had detectable antibody levels against poliovirus type 1. Fewer children at 8-9 years of age had antibodies against poliovirus type 3 than 3-4 year-olds (78%vs. 89% P < 0.001). A significant overall lower proportion of 8-9 year-old children had detectable tetanus toxoid antibodies compared to 3-4 year-old children (87%vs. 95% P < 0.001), as well as those who received four doses of DPT (90%vs. 97% P < 0.001). Conclusions High vaccine coverage is achieved in The Gambia with EPI. With time the number of vaccinated children who are not protected against measles, poliovirus 3 and tetanus increases. Besides the maintenance of high vaccine coverage in infants and young children, booster doses of some of the EPI vaccines in adolescents should be considered.

Multiplexed immunoassays by flow cytometry for diagnosis and surveillance of infectious diseases in resource-poor settings

An accurate, rapid and cost-effective diagnosis is the cornerstone of efficient clinical and epidemiological management of infections. Here we discuss the relevance of an emerging technology, multiplexed immunoassays read by flow cytometry, for the diagnosis of infectious diseases. In these assays, multiple fluorescent microspheres, conjugated to different antigens or antibodies, constitute the solid phase for detecting antibodies or antigens in biological samples. These assays seem to be more sensitive than traditional immunoassays, have a high throughput capacity, and provide a wide analytical dynamic range. Additionally, they have multiplexing ability-ie, they are capable of measuring multiple antibodies or antigens simultaneously. We discuss four different areas where this technology could make an impact in resource-poor settings: (i) infections causing rash and fever in children; (ii) sero-epidemiological studies on vaccine-preventable diseases; (iii) management of genital ulcers and vaginal discharge; and (iv) screening of infections in blood banking. We predict a widespread use for a new breed of small, affordable, practical flow cytometers as field instruments for replacing ELISA and RIA tests, which will also be capable of doing cellular immunological tests such as CD4+ T-cell enumeration and Plasmodium falciparum detection in whole blood.

Determinants of mortality among children in the urban slums of Dhaka city, Bangladesh

The growing slum population in the developing world is an increasing challenge for local health authorities. Little is known of the patterns of disease occurrence including treatment types offered in this population. The paper describes reported child mortality and its determinants, including the main diseases affecting children and treatments, in the slum population of Dhaka city, Bangladesh. 1500 households in three slum communities were included in a cross-sectional survey. Reported death rates in the households per 1000 children (0-107 months) within the last year from the interview were 20.5 for boys and 27.0 for girls. More girls than boys died in infancy (age < 12 months). The most frequent reported causes of deaths were tetanus in infancy and diarrhoea among children aged < or = 12 months. Vaccination coverage (DPT, polio, measles and BCG) was 73% for children < 3 years of age. The results showed that gender difference in mortality may have been influenced by the patterns of treatment received during sickness and the choice of treatment was determined by the financial ability of the households. Household income, children's vaccinations, TT immunization of mothers and personal cleanliness appeared to be significantly associated with child mortality. Despite the relatively high vaccination coverage for this population, child mortality remained alarmingly high, indicating that socioeconomic and environmental conditions must be improved to substantially reduce morbidity and mortality in this population.