Early two-dose measles vaccination schedule in Guinea-Bissau: good protection and coverage in infancy

Predictors for low coverage of uptake of second dose of measles vaccine among children in sub-Saharan Africa, 2023: a systematic review and meta-analysis

Background

Measles became a public health important disease in sub-Saharan Africa. World Health Organization recommended measles-containing vaccine dose 2 (MCV2) through routine service delivery. This study aims to determine coverage of second-dose measles vaccination uptake and its predictors among children aged 24-35 months in sub-Saharan Africa.

Methods and materials

We conducted an extensive search of literature as indicated in the guideline of reporting systematic review and meta-analysis (PRISMA). The databases used were PubMed, Google Scholar, and HINARI literature.

Results

The overall uptake of the second dose of measles vaccine uptake was 41% (95% CI: 28.90-53.47). Caregiver's awareness of the importance of the second dose of measles (2.51, 95% CI 1.77, 3.25), educational status of mothers (1.30, 95% CI 1.16, 1.45), distance from vaccination site (1.22, 95% CI 1.12, 1.32), and attending four and above ANC visit (2.72, 95% CI 2.29, 3.15) were determinants for second dose measles vaccine uptake.

Conclusion

Coverage of the second dose of measles uptake in Sub-Saharan Africa was low (41%) which is lower than the recommendation from WHO. Therefore policymakers and stakeholders should increase mother's awareness. Also, special strategies should be developed for those who are far from the vaccination site.

Abbreviation and acronyms

ANC: Ante Natal Care; JBI: Joanna Briggs Institute; MCV1: Measles containing vaccine dose 1; MCV2: Measles containing vaccine dose 2; WHO: World Health Organization.

Exploring spatial variations and the individual and contextual factors of uptake of measles-containing second dose vaccine among children aged 24 to 35 months in Ethiopia

BACKGROUND

To eliminate measles, which is a devastating contagious disease, Ethiopia introduced the measles-containing second dose vaccine (MCV2) that will be given in the second year of life. Despite its paramount benefit, the coverage was low worldwide and, in Ethiopia, there is scarce evidence on the geographic variations and factors associated with uptake of MCV2.

OBJECTIVE

This study aimed to explore the spatial variations and the individual and contextual factors of uptake of measles-containing second dose vaccine among children aged 24 to 35 months in Ethiopia.

METHODS

We used the 2019 Ethiopian Mini Demographic and Health Survey data. A total weighted sample of 800 children aged 24 to 35 months was used. Multilevel analysis was employed and an adjusted odds ratio (AOR) with a 95% confidence interval (CI) was reported. Factors with a p-value<0.05 in the multivariable analysis were declared to be significant predictors of MCV2 uptake. To explore the spatial variations of MCV2 uptake, we have conducted spatial analysis using both Arc GIS version 10.7 and SaTScan version 9.6 software.

RESULTS

The proportion of MCV2 uptake was 9.84% (95% CI: 7.96%, 12.11%). Children whose mothers were aged 20-34 years (AOR = 0.19; 95%CI: 0.05, 0.69) and 35-49 years (AOR = 0.21; 95%CI: 0.04, 0.90), being the 4th-5th child (AOR = 4.02; 95%CI: 1.45, 11.14) and 6th and above child (AOR = 4.12; 95%CI: 1.42, 13.05) and children who did not receive full childhood vaccinations (AOR = 0.44; 95%CI: 0.25, 0.77) were significantly associated with MCV2 uptake. Besides, MCV2 uptake was clustered in Ethiopia (Global Moran's I = 0.074, p-value <0.01). The primary cluster spatial window was detected in the Benishangul-Gumuz region with LLR = 10.05 and p = 0.011.

CONCLUSION

The uptake of MCV2 in Ethiopia was low. Maternal age, birth order, and uptake of the other basic vaccines were associated with MCV2 uptake. Besides, MCV2 uptake was clustered in Ethiopia and the primary cluster spatial window was located in the Benishangul-Gumuz region. Therefore, special concern should be given to regions with lower MCV2 uptake such as the Benishangul-Gumuz region. Besides, it is better to give attention to basic vaccination programs.

Measles second dose vaccine utilization and associated factors among children aged 24–35 months in Sub-Saharan Africa, a multi-level analysis from recent DHS surveys

Background

Although a safe and effective vaccine is available, measles remains an important cause of mortality and morbidity among young children in Sub-Saharan Africa (SSA). The WHO and UNICEF recommended measles-containing vaccine dose 2 (MCV2) in addition to measles-containing vaccine dose 1 (MCV1) through routine services strategies. Many factors could contribute to the routine dose of MCV2 coverage remaining far below targets in many countries of this region. This study aimed to assess the prevalence of MCV2 utilization among children aged 24–35 months and analyze factors associated with it by using recent nationally representative surveys of SSA countries.

Methods

Secondary data analysis was done based on recent Demographic and Health Surveys (DHS) data from eight Sub-Saharan African countries. In this region, only eight countries have a record of routine doses of measles-containing vaccine dose 2 in their DHS dataset. The multilevel binary logistic regression model was fitted to identify significantly associated factors. Variables were extracted from each of the eight country’s KR files. Adjusted Odds Ratios (AOR) with a 95% Confidence Interval (CI) and p-value ≤ 0.05 in the multivariable model were used to declare significant factors associated with measles-containing vaccine dose 2 utilization.

Result

The pooled prevalence of MCV2 utilization in SSA was 44.77% (95% CI: 27.10–62.43%). In the multilevel analysis, mothers aged 25–34 years [AOR = 1.15,95% CI (1.05–1.26), mothers aged 35 years and above [AOR = 1.26, 95% CI (1.14–1.41)], maternal secondary education and above [AOR = 1.27, 95% CI (1.13–1.43)], not big problem to access health facilities [AOR = 1.21, 95% CI (1.12–1.31)], four and above ANC visit [AOR = 2.75, 95% CI (2.35–3.24)], PNC visit [AOR = 1.13, 95% CI (1.04–1.23)], health facility delivery [AOR = 2.24, 95% CI (2.04–2.46)], were positively associated with MCV2 utilization. In contrast, multiple twin [AOR = 0.70, 95% CI (0.53–0.95)], rural residence [AOR = 0.69, 95% CI (0.57–0.82)] and high community poverty [AOR = 0.66, 95% CI (0.54–0.80)] were found to be negatively associated with MCV2 utilization.

Conclusions and recommendations

Measles-containing vaccine doses 2 utilization in Sub-Saharan Africa was relatively low. Individual-level factors and community-level factors were significantly associated with low measles-containing vaccine dose 2 utilization. The MCV2 utilization could be improved through public health intervention by targeting rural residents, children of uneducated mothers, economically poor women, and other significant factors this study revealed.

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.

Measles virus antibody responses in children randomly assigned to receive standard-titer edmonston-zagreb measles vaccine at 4.5 and 9 months of age, 9 months of age, or 9 and 18 months of age

The World Health Organization recommends administration of measles vaccine (MV) at age 9 months in low-income countries. We tested the measles virus antibody response at 4.5, 9, 18, and 24 months of age for children randomly assigned to receive standard-titer Edmonston-Zagreb MV at 4.5 and 9 months, at 9 months, or at 9 and 18 months of age. At 4.5 months of age, 75% had nonprotective measles virus antibody levels. Following receipt of MV at 4.5 months of age, 77% (316/408) had protective antibody levels at 9 months of age; after a second dose at 9 months of age, 97% (326/337) had protective levels at 24 months of age. In addition, the response at both 9 and 24 months of age was inversely correlated with the antibody level at receipt of the first dose of MV, and the second dose of MV, received at 9 months of age, provided a significant boost in antibody level to children who had low antibody levels. In the group of 318 children who received MV at 9 months of age, with or without a second dose at 18 months of age, 99% (314) had protective levels at 24 months of age. The geometric mean titer at 24 months of age was significantly lower in the group that received MV at 4.5 and 9 months of age than in the group that received MV at 9 months of age (P = .0001). In conclusion, an early 2-dose MV schedule was associated with protective measles virus antibody levels at 24 months of age in nearly all children. Clinical Trials Registration. NCT00168558.

Measles antibody levels after vaccination with Edmonston-Zagreb and Schwarz measles vaccine at 9 months or at 9 and 18 months of age: a serological study within a randomised trial of different measles vaccines

Standard-titre Schwarz (SW) and Edmonston-Zagreb (EZ) measles vaccines (MV) are both used in the routine immunisation programme. Within a trial of different strains of MV, we examined antibody responses in both one-dose and two-dose schedules when the first dose was administered at 9 months.

SETTING AND METHODS

The trial was conducted in an urban area in Guinea-Bissau where we have had a health and demographic surveillance system and studied strategies to prevent measles infection since 1978. In the present study, children were randomised to SW or EZ as the first MV and furthermore randomised to a second dose of the same MV or no vaccine at 18 months of age. We obtained blood samples from 996 children at baseline; post-vaccination blood samples were collected at 18 and 24 months of age to assess measles antibody levels after one or two doses of MV.

RESULTS

At age 18 months all had responded to the first dose and only 1% (8/699) of the children had non-protective antibody levels irrespective of vaccine type. SW was associated with significantly higher levels of measles antibodies (geometric mean titre (GMT)=2114 mIU/mL (95%CI 1153-2412)) than EZ (GMT=807 mIU/mL (722-908)) (p=0.001). Antibody concentration was significantly higher in girls than in boys after EZ but not after SW. Antibody levels were higher in the rainy than the dry season. There was no clear indication that a booster dose at 18 months increased the antibody level at 24 months of age.

CONCLUSIONS

Maternal antibody levels have declined significantly in recent years and 99% had protective levels of measles antibody following primary MV at 9 months of age. It is unlikely that measles prevention and child health will be improved by increasing the age of MV as currently recommended.

Immunological impact of an additional early measles vaccine in Gambian children: responses to a boost at 3 years

BACKGROUND

Measles vaccine in early infancy followed by a dose at 9 months of age protects against measles and enhances child survival through non-specific effects. Little is known of immune responses in the short or long term after booster doses.

METHODS

Infants were randomized to receive measles vaccine at 9 months of age (group 1) or 4 and 9 months of age (group 2). Both groups received a boost at 36 months of age. T-cell effector and memory responses using IFN-γ ELIspot and cytokine assays and antibody titres using a haemagglutination-inhibition assay were compared at various times.

RESULTS

Vaccination at 4 months of age elicited antibody and CD4 T-cell mediated immune responses .Two weeks after vaccination at 9 months of age group 2 had much higher antibody titres than group1 infants; cell-mediated effector responses were similar. At 36 months of age group 2 antibody titres exceeded protective levels but were 4-fold lower than group 1; effector and cytokine responses were similar. Re-vaccination resulted in similar rapid and high antibody titres in both groups (median 512); cellular immunity changed little. At 48 months of age group 2 antibody concentrations remained well above protective levels though 2-fold lower than group 1; T-cell memory was readily detectable and similar in both groups.

CONCLUSIONS

An additional early measles vaccine given to children at 4 months of age induced a predominant CD4 T-cell response at 9 months and rapid development of high antibody concentrations after booster doses. However, antibody decayed faster in these children than in the group given primary vaccination at 9 months of age. Cellular responses after 9 months were generally insignificantly different.

The optimal age of measles immunisation in low-income countries: a secondary analysis of the assumptions underlying the current policy

OBJECTIVE

The current policy of measles vaccination at 9 months of age was decided in the mid-1970s. The policy was not tested for impact on child survival but was based on studies of seroconversion after measles vaccination at different ages. The authors examined the empirical evidence for the six underlying assumptions.

DESIGN

Secondary analysis.

DATA SOURCES AND METHODS

These assumptions have not been research issues. Hence, the authors examined case reports to assess the empirical evidence for the original assumptions. The authors used existing reviews, and in December 2011, the authors made a PubMed search for relevant papers. The title and abstract of papers in English, French, Portuguese, Spanish, German and Scandinavian languages were assessed to ascertain whether the paper was potentially relevant. Based on cumulative measles incidence figures, the authors calculated how many measles cases had been prevented assuming everybody was vaccinated at a specific age, how many 'vaccine failures' would occur after the age of vaccination and how many cases would occur before the specific age of vaccination. In the combined analyses of several studies, the authors used the Mantel-Haenszel weighted RR stratifying for study or age groups to estimate common trends.

SETTING AND PARTICIPANTS

African community studies of measles infection.

PRIMARY AND SECONDARY OUTCOMES

Consistency between assumptions and empirical evidence and the predicted effect on mortality.

RESULTS

In retrospect, the major assumptions were based on false premises. First, in the single study examining this point, seronegative vaccinated children had considerable protection against measles infection. Second, in 18 community studies, vaccinated measles cases ('vaccine failures') had threefold lower case death than unvaccinated cases. Third, in 24 community studies, infants had twofold higher case death than older measles cases. Fourth, the only study examining the assumption that 'vaccine failures' lead to lack of confidence found the opposite because vaccinated children had milder measles infection. Fifth, a one-dose policy was recommended. However, the two randomised trials of early two-dose measles vaccination compared with one-dose vaccination found significantly reduced mortality until 3 years of age. Thus, current evidence suggests that the optimal age for a single dose of measles vaccine should have been 6 or 7 months resulting in fewer severe unvaccinated cases among infants but more mild 'vaccine failures' among older children. Furthermore, the two-dose trials indicate that measles vaccine reduces mortality from other causes than measles infection.

CONCLUSIONS

Many lives may have been lost by not determining the optimal age of measles vaccination. Since seroconversion continues to be the basis for policy, the current recommendation is to increase the age of measles vaccination to 12 months in countries with limited measles transmission. This policy may lead to an increase in child mortality.

Risk factors for measles in young infants in an urban African area with high measles vaccination coverage

BACKGROUND

We examined risk factors for measles infection before measles vaccination at 9 months of age in Guinea-Bissau.

METHODS

Among 1524 children enrolled in a trial of early measles vaccination at 4.5 months of age, we assessed the relative risk (RR) of measles before enrollment and the incidence rate ratio between 4.5 and 9 months of age for different groups.

RESULTS

The incidence was high, with 4% having measles before 4.5 months and 10% having measles between 4.5 and 9 months of age. The main risk factor was the age of the mother; children of young mothers (age, 15-24 years) had lower antibody titers and higher risk of measles than children of older mothers both before 4.5 months (RR = 1.74 [1.02-2.96]) and between 4.5 and 9 months of age (incidence rate ratio = 1.59 [1.05-2.41]). Having no Bacillus Calmette-Guérin scar was associated with a higher risk of measles before 4.5 months of age (RR = 2.61 [1.54-4.45]). Children who were not breast-fed and had fever or respiratory infection at enrollment had a 2- to 4-fold higher risk of measles between 4.5 and 9 months of age.

INTERPRETATION

Young mothers transmit lower titers of antibodies to their children and an increasing proportion of infants become susceptible to measles before the age of measles vaccination.

Non-specific effects of standard measles vaccine at 4.5 and 9 months of age on childhood mortality: randomised controlled trial

OBJECTIVE

To examine in a randomised trial whether a 25% difference in mortality exists between 4.5 months and 3 years of age for children given two standard doses of Edmonston-Zagreb measles vaccines at 4.5 and 9 months of age compared with those given one dose of measles vaccine at 9 months of age (current policy).

DESIGN

Randomised controlled trial.

SETTING

The Bandim Health Project, Guinea-Bissau, which maintains a health and demographic surveillance system in an urban area.

PARTICIPANTS

6648 children aged 4.5 months of age who had received three doses of diphtheria-tetanus-pertussis vaccine at least four weeks before enrolment. A large proportion of the children (80%) had previously taken part in randomised trials of neonatal vitamin A supplementation.

INTERVENTION

Children were randomised to receive Edmonston-Zagreb measles vaccine at 4.5 and 9 months of age (group A), no vaccine at 4.5 months and Edmonston-Zagreb measles vaccine at 9 months of age (group B), or no vaccine at 4.5 months and Schwarz measles vaccine at 9 months of age (group C). Main outcome measure Mortality rate ratio between 4.5 and 36 months of age for group A compared with groups B and C. Secondary outcomes tested the hypothesis that the beneficial effect was stronger in the 4.5 to 9 months age group, in girls, and in the dry season, but the study was not powered to test whether effects differed significantly between subgroups.

RESULTS

In the intention to treat analysis of mortality between 4.5 and 36 months of age the mortality rate ratio of children who received two doses of Edmonston-Zagreb vaccine at 4.5 and 9 months of age compared with those who received a single dose of Edmonston-Zagreb vaccine or Schwarz vaccine at 9 months of age was 0.78 (95% confidence interval 0.59 to 1.05). In the analyses of secondary outcomes, the intention to treat mortality rate ratio was 0.67 (0.38 to 1.19) between 4.5 and 9 months and 0.83 (0.83 to 1.16) between 9 and 36 months of age. The effect on mortality between 4.5 and 36 months of age was significant for girls (intention to treat mortality rate ratio 0.64 (0.42 to 0.98)), although this was not significantly different from the effect in boys (0.95 (0.64 to 1.42)) (interaction test, P=0.18). The effect did not differ between the dry season and the rainy season. As neonatal vitamin A supplementation is not WHO policy, the analyses were done separately for the 3402 children who did not receive neonatal vitamin A. In these children, the two dose Edmonston-Zagreb measles vaccine schedule was associated with a significantly lower mortality between 4.5 and 36 months of age (intention to treat mortality rate ratio 0.59 (0.39 to 0.89)). The effect was again significant for girls but not statistically significant from the effect in boys. When measles cases were censored, the intention to treat mortality rate ratio was 0.65 (0.43 to 0.99).

CONCLUSIONS

Although the overall effect did not reach statistical significance, the results may indicate that a two dose schedule with Edmonston-Zagreb measles vaccine given at 4.5 and 9 months of age has beneficial non-specific effects on children's survival, particularly for girls and for children who have not received neonatal vitamin A. This should be tested in future studies in different locations.

TRIAL REGISTRATION

Clinical trials NCT00168558.

Modelling the first dose of measles vaccination: the role of maternal immunity, demographic factors, and delivery systems

Measles vaccine efficacy is higher at 12 months than 9 months because of maternal immunity, but delaying vaccination exposes the children most vulnerable to measles mortality to infection. We explored how this trade-off changes as a function of regionally varying epidemiological drivers, e.g. demography, transmission seasonality, and vaccination coverage. High birth rates and low coverage both favour early vaccination, and initiating vaccination at 9-11 months, then switching to 12-14 months can reduce case numbers. Overall however, increasing the age-window of vaccination decreases case numbers relative to vaccinating within a narrow age-window (e.g. 9-11 months). The width of the age-window that minimizes mortality varies as a function of birth rate, vaccination coverage and patterns of access to care. Our results suggest that locally age-targeted strategies, at both national and sub-national scales, tuned to local variation in birth rate, seasonality, and access to care may substantially decrease case numbers and fatalities for routine vaccination.

Effectiveness of measles vaccination and vitamin A treatment

BACKGROUND

The current strategy utilized by WHO/United Nations Children's Fund (UNICEF) to reach the Global Immunization Vision and Strategy 2010 measles reduction goal includes increasing coverage of measles vaccine, vitamin A treatment and supplementation in addition to offering two doses of vaccine to all children.

METHODS

We conducted a systematic review of published randomized controlled trials (RCTs) and quasi-experimental (QE) studies in order to determine effect estimates of measles vaccine and vitamin A treatment for the Lives Saved Tool (LiST). We utilized a standardized abstraction and grading format in order to determine effect estimates for measles mortality employing the standard Child Health Epidemiology Research Group Rules for Evidence Review.

RESULTS

We identified three measles vaccine RCTs and two QE studies with data on prevention of measles disease. A meta-analysis of these studies found that vaccination was 85% [95% confidence interval (CI) 83-87] effective in preventing measles disease, which will be used as a proxy for measles mortality in LiST for countries vaccinating before one year of age. The literature also suggests that a conservative 95% effect estimate is reasonable to employ when vaccinating at 1 year or later and 98% for two doses of vaccine based on serology reviews. We included six high-quality RCTs in the meta-analysis of vitamin A treatment of measles which found no significant reduction in measles morality. However, when stratifying by vitamin A treatment dose, at least two doses were found to reduce measles mortality by 62% (95% CI 19-82).

CONCLUSION

Measles vaccine and vitamin A treatment are effective interventions to prevent measles mortality in children.

Thymus size at 6 months of age and subsequent child mortality

OBJECTIVE

To examine determinants of thymus size at age 6 months and investigate whether thymus size at this age is a determinant of subsequent mortality.

STUDY DESIGN

Thymus size was measured by transsternal sonography in 923 6-month-old children participating in a measles vaccination trial in Guinea-Bissau.

RESULTS

Thymus size was strongly associated with anthropometric measurements. Boys had larger thymuses than girls, controlling for anthropometry. Crying during sonography made the thymus appear smaller. Children who were not vaccinated with Bacille Calmette-Guérin (BCG) or were vaccinated with BCG in the preceding 4 weeks before inclusion into the study had larger thymuses. Children who had malaria or had been treated with chloroquine or Quinimax in the previous week before inclusion had smaller thymuses. Controlled for background factors associated with thymus size and mortality, small thymus size remained a strong and independent risk factor for mortality (hazard ratio = 0.31; 95% confidence interval = 0.18 to 0.52).

CONCLUSIONS

Small thymus size at age 6 months is a strong risk factor for mortality. To prevent unnecessary deaths, it is important to identify preventable factors predisposing to small thymus size.

Protective efficacy of standard Edmonston-Zagreb measles vaccination in infants aged 4.5 months: interim analysis of a randomised clinical trial

OBJECTIVE

To examine the protective efficacy of measles vaccination in infants in a low income country before 9 months of age.

DESIGN

Randomised clinical trial.

PARTICIPANTS

1333 infants aged 4.5 months: 441 in treatment group and 892 in control group.

SETTING

Urban area in Guinea-Bissau.

INTERVENTION

Measles vaccination using standard titre Edmonston-Zagreb vaccine at 4.5 months of age.

MAIN OUTCOME MEASURES

Vaccine efficacy against measles infection, admission to hospital for measles, and measles mortality before standard vaccination at 9 months of age.

RESULTS

28% of the children tested at 4.5 months of age had protective levels of maternal antibodies against measles at enrolment. After early vaccination against measles 92% had measles antibodies at 9 months of age. A measles outbreak offered a unique situation for testing the efficacy of early measles vaccination. During the outbreak, 96 children developed measles; 19% of unvaccinated children had measles before 9 months of age. The monthly incidence of measles among the 441 children enrolled in the treatment arm was 0.7% and among the 892 enrolled in the control arm was 3.1%. Early vaccination with the Edmonston-Zagreb measles vaccine prevented infection; vaccine efficacy for children with serologically confirmed measles and definite clinical measles was 94% (95% confidence interval 77% to 99%), for admissions to hospital for measles was 100% (46% to 100%), and for measles mortality was 100% (-42% to 100%). The number needed to treat to prevent one case of measles between ages 4.5 months and 9 months during the epidemic was 7.2 (6.8 to 9.2). The treatment group tended to have lower overall mortality (mortality rate ratio 0.18, 0.02 to 1.36) although this was not significant.

CONCLUSIONS

In low income countries, maternal antibody levels against measles may be low and severe outbreaks of measles can occur in infants before the recommended age of vaccination at 9 months. Outbreaks of measles may be curtailed by measles vaccination using the Edmonston-Zagreb vaccine as early as 4.5 months of age. TRIAL REGISTRATION CLINICAL TRIALS: NCT00168558 [ClinicalTrials.gov].

Increased female-male mortality ratio associated with inactivated polio and diphtheria-tetanus-pertussis vaccines: Observations from vaccination trials in Guinea-Bissau

BACKGROUND

The 2-fold increase in female mortality after high-titer measles vaccine may have occurred because many children received diphtheria-tetanus-pertussis (DTP) vaccine or inactivated polio vaccine (IPV) after high-titer measles vaccine.

OBJECTIVE

We examined whether DTP vaccine and IPV were associated with increased female mortality when they were the most recent vaccine administered to children who had not received measles vaccine.

SETTING AND DESIGN

IPV was used as a control vaccine in 4 randomized trials of early measles vaccination (MV) with enrollment at 4-6 months of age conducted in Guinea-Bissau. Many children had not received all 3 DTP vaccinations before enrollment, and therefore received DTP after IPV or MV. We examined whether DTP vaccination status at enrollment affected the female-male mortality ratio.

POPULATION

9544 children enrolled in 4 trials.

MAIN OUTCOME MEASURE

The female-male mortality ratio in different vaccine groups.

RESULTS

Females had a higher mortality rate than males among children randomized to receive IPV (mortality rate ratio [MR] 1.52, 95% CI 1.02-2.28), but females had a similar mortality rate to males among children randomized to receive MV (MR 1.01, 0.69-1.46) and among children in the IPV group after they had received MV at 9 months of age or later (MR 0.88, 0.68-1.14). Children who had not received a third dose of DTP before enrollment (and were likely to receive DTP after MV or IPV) tended to have a higher mortality than children who had received all 3 doses of DTP (MR 1.30, 0.97-1.73). This effect was seen only among girls (MR 1.61, 1.08-2.40) and not among boys (MR 1.02, 0.67-1.54). Girls had a lower mortality when MV was the most recent vaccine received rather than DTP or IPV (MR 0.49, 0.28-0.87).

CONCLUSIONS

Randomization to IPV was associated with higher female than male mortality. However, the increased female mortality might result from additional doses of DTP received after enrollment and before measles vaccination.

Prophylactic antibiotics to prevent pneumonia and other complications after measles: community based randomised double blind placebo controlled trial in Guinea-Bissau

OBJECTIVE

To investigate whether prophylactic antibiotics can prevent complications of measles.

DESIGN

Community based, randomised, double blind, placebo controlled trial.

SETTING

Bandim Health Project study area in Bissau, Guinea-Bissau, west Africa.

PARTICIPANTS

84 patients with measles during a measles epidemic in Bissau in 1998 (fewer than originally planned owing to interruption by war).

INTERVENTIONS

Sulfamethoxazole-trimethoprim (co-trimoxazole) or placebo for seven days.

MAIN OUTCOME MEASURES

Pneumonia and admission to hospital. Also weight change during the first month of infection, diarrhoea, severe fever, oral thrush, stomatitis, conjunctivitis, and otitis media.

RESULTS

The median age of the patients with measles was 5.4 (range 0.49-24.8) years. One of 46 participants who received co-trimoxazole developed pneumonia, in contrast to six of 38 participants who received placebo (odds ratio 0.08 (95% confidence interval 0 to 0.56), adjusted for age group). The number needed to treat was 7 (4 to 48). All three participants admitted to hospital had received placebo (P=0.09). The weight gain during the first month after inclusion was 15 (2-29) g/day in the placebo group and 32 (23-42) g/day in the co-trimoxazole group (P=0.04, adjusted for age group, weight for age at inclusion, measles vaccination status, and duration of disease). Significantly less conjunctivitis occurred among recipients of co-trimoxazole than placebo, as well as a non-significant tendency to less diarrhoea, severe fever, oral thrush, and stomatitis. Complications of otitis media were the same in the two groups.

CONCLUSIONS

The group that received prophylactic antibiotics had less pneumonia and conjunctivitis and had significantly higher weight gains in the month after inclusion. The results indicate that prophylactic antibiotics may have an important role in the management of measles infection in low income countries.

TRIAL REGISTRATION

Clinical trials NCT00168532.

Childhood mortality after oral polio immunisation campaign in Guinea-Bissau

Though previous studies have suggested a non-specific beneficial effect of oral polio vaccine (OPV), there has been no evaluation of the mortality impact of national polio immunization days. On the other hand, studies examining the effect of OPV and diphtheria-tetanus-pertussis (DTP) vaccines, which are usually administered together in routine immunisation programmes in low-income countries, have found no beneficial or even a negative effect on infant survival. In 1998, we used the opportunity of two national immunisation days to examine the impact of OPV administered alone on survival for the 6103 children less than 5 years of age in the Bandim Health Project's study area in Guinea-Bissau. Survival was ascertained through regular surveillance from March 1998 until the beginning of the war on June 7, 1998, the end of 1998, or the end of 1999, respectively. The child register was linked with a register for the only paediatric ward in Bissau to determine the risk of hospitalisations. Among children under 5 years of age, 82% had received 1 or 2 doses of polio vaccines during the campaign. Though polio vaccination during the campaign was associated with slightly lower mortality, this difference was not significant for all children under 5 years of age (mortality ratio (MR)=0.46 (0.18-1.15)). However, oral polio vaccination was associated with a beneficial effect for children under 6 months of age at the time of the campaign, the mortality ratio being 0.09 (95% CI 0.01-0.85) in the 3 months before the war controlling for significant background factors, including routine immunizations, antenatal consultations, and arm circumference. The polio-vaccinated children aged 0-5 months had fewer hospitalisations than children who had not been polio vaccinated (RR=0.27 (0.10-0.76)). With longer follow-up to December 1998 or December 1999, the difference in mortality gradually disappeared, the MR for polio-vaccinated children being 0.61 (0.32-1.14) and 0.83 (0.51-1.34), respectively. Among children aged 6-59 months of age, measles vaccine was associated with a 56% reduction in mortality (MR=0.44 (0.28-0.69)) and no effect of oral polio vaccine was measurable in this age group. The effect of polio vaccine among children less than 6 months of age could be due to selection bias but might also represent a non-specific beneficial immune stimulation and there is nothing to suggest that OPV might have a negative effect on infant survival. Studies of the possible non-specific effects of oral polio vaccine are warranted before OPV is withdrawn.

Routine vaccinations associated with divergent effects on female and male mortality at the paediatric ward in Bissau, Guinea-Bissau

Several studies have suggested that routine childhood immunisations may have non-specific effects on mortality. To examine which disease categories might be affected, we investigated whether immunisation status had an impact on the case fatality for hospitalised children. Between 1990 and 1996, the Bandim Health Project maintained a register of all children from the study area hospitalised at the paediatric ward of the central hospital in Bissau, Guinea-Bissau. The study included 2079 hospitalised children aged 1.5-17 months coming from the Bandim study area. Among children whose vaccination card had been seen at admission, the case fatality ratio for measles-vaccinated children versus measles-unvaccinated children was 0.51 (0.27-0.98), the beneficial effect being significantly stronger for girls than for boys (test of interaction, p=0.050). The protective effect of measles vaccine remained unchanged when hospitalised measles cases were excluded from the analysis (0.49 (0.26-0.94)). The effect of measles vaccine was strongest for children with pneumonia (MR=0.28 (0.07-0.91)) and presumptive malaria (MR=0.40 (0.13-1.18)). For measles-vaccinated children, the female to male case fatality ratio was 0.54 (0.28-0.97). Among children having received diphtheria-tetanus-pertussis (DTP) and oral polio (OPV) as the last vaccines, girls had higher case fatality than boys, the mortality ratio being 1.63 (1.03-2.59). The female to male ratios were significantly inversed for DTP and OPV versus measles vaccine (test of interaction, p=0.003). These results remained unchanged if 1-month post-discharge deaths were included in the analysis, and in multivariate analyses controlling for determinants of mortality. In conclusion, measles vaccine was associated with reduced mortality from diseases other than measles, the beneficial effect being stronger for girls than for boys. On the other hand, DTP and OPV vaccine were associated with higher case fatality for girls than for boys. Understanding the divergent non-specific effects of common vaccines may contribute to better child survival in developing countries.

Vaccination technique, PPD reaction and BCG scarring in a cohort of children born in Guinea-Bissau 2000-2002

The rates of positive tuberculin skin test (TST) reactions and BCG scarring after BCG vaccination vary between studies and populations. Tuberculin reactivity and BCG scarring may be related to better child survival in low-income countries. We therefore studied determinants for TST reaction and scarring in Guinea-Bissau. In a cohort of children born in suburban Bissau from March 2000 to July 2002, we assessed a Mantoux test with Purified protein derivative (PPD) (SSI, 2 T.U.) at 2 (2689 children), 6 (N=2148) and 12 months (N=1638) of age, and BCG scar was assessed at 2 (N=2698) and 6 months (N=2225) of age. In a subgroup of the children the vaccination technique was monitored by direct observation of post-vaccination wheal and route of administration. Three different types of BCG vaccine supplied by the local Extended Programme on Immunization were used. At 6 months of age the rate of PPD reactors (>1mm) after BCG vaccination was 25% and the rate of scarring was 89%. One BCG strain was associated with fewer PPD reactors (OR=0.54 (0.31-0.91)) and BCG scars (OR=0.13 (0.05-0.37)) and larger post-vaccination wheals produced more PPD reactions (OR 1.21 (95% CI 1.02-1.43)) and BCG scars (OR 1.66 (1.24-2.21)). In the multivariable analyses of BCG-vaccinated children assessed at 6 months of age, monitoring of vaccination technique and type of BCG vaccine were important. This was not changed by control for other determinants, including sex, season, vaccination place, birthplace, ethnic group, low birth weight, place of residence, education and civil status of mother. We reason that vaccination technique and BCG strain are important for PPD reaction and scarring in response to BCG vaccination. Considering that these responses are associated with better infant survival, the importance of monitoring vaccination technique and of different BCG strains should be evaluated with respect to infant mortality.

Low birth weight infants and Calmette-Guérin bacillus vaccination at birth: community study from Guinea-Bissau

BACKGROUND

In developing countries, low birth weight (LBW) children are often not vaccinated with Calmette-Guérin bacillus (BCG) at birth. Recent studies have suggested that BCG may have a nonspecific beneficial effect on infant mortality. We evaluated the consequences of not vaccinating LBW children at birth in Guinea-Bissau.

METHODS

Between 1989 and 1999, 7138 children born at the central hospital had a birth weight registered. We assessed BCG coverage until 3 years of age. Data on tuberculin skin test (TST) for 297 children and BCG scar for 1319 children in the study population were reanalyzed for differences between normal birth weight (NBW) children and LBW children. We assessed the effect of early BCG vaccination on mortality to 12 months of age.

RESULTS

Among LBW children there were 1.5- to 3-fold more unvaccinated individuals than among NBW children up to 4 months of age. There was no overall difference between LBW and NBW children in TST or BCG scarring; LBW children vaccinated early may have had slightly reduced reactions to tuberculin. Among 845 LBW children, 182 had received BCG within the first week of life. Controlling for background factors and censoring at first diphtheria-tetanuspertussis vaccination, measles vaccination or at 6 months of age (whichever came first), the mortality rate ratio for BCG-vaccinated versus -unvaccinated LBW children was 0.17 (95% confidence interval, 0.06-0.49), with an even stronger effect for LBW children vaccinated in the first week of life (mortality rate ratio, 0.07; 95% confidence interval, 0.01-0.62).

CONCLUSIONS

The policy of not vaccinating with BCG at birth had a negative impact on vaccination coverage for LBW children. Early BCG vaccination had no large negative impact on TST and BCG scarring. Mortality was lower for BCG-vaccinated than for unvaccinated LBW children controlling for available background factors. BCG vaccination of LBW children may have a beneficial effect on survival that cannot be explained by protection against tuberculosis. Future studies should examine possible adverse effects from equalizing BCG policy for LBW and NBW children.

Survival of previously measles-vaccinated and measles-unvaccinated children in an emergency situation: an unplanned study

BACKGROUND

Previous studies have suggested that standard measles vaccine may reduce mortality by more than the number of deaths thought to be caused by measles infection in areas with high mortality. However, these observations have not been based on randomized trials.

METHODS

During the recent war in Guinea-Bissau, most children fled from the city of Bissau and immunization services in the country broke down for several months. We were performing a trial in which children were randomized at 6 months of age to receive either measles vaccine or inactivated polio vaccine. Because of the war many children did not receive the dose of measles vaccine planned for 9 months of age. We were able to monitor mortality during the war and after.

RESULTS

Included in the study were 433 children 6 to 11 months of age. Fifteen children died (3.6%) during the first 3 months of the war before vaccination programs were resumed, 4 of 214 measles-vaccinated children and 11 of 219 children who had received inactivated polio vaccine. The effect of measles vaccine was marked for girls [mortality rate ratio (MR), 0.00; 95% confidence limits, 0.0 to 0.37], whereas there was no difference for boys (MR = 1.02; 95% confidence limits, 0.25 to 3.88). In a combined analysis controlling for factors that differed between the two groups, the MR for measles-vaccinated children was 0.30 (95% confidence limits, 0.08 to 0.87). Prolonging the period of observation to the end of 1998 or including the prewar period did not modify the significant beneficial effect of measles vaccine for girls. Twenty-two of the children in the cohort were reported to have had measles, 8 cases occurring during the 3 months of the war. Exclusion of measles cases in the analysis did not change the results; children who had received measles vaccine had a MR of 0.28 (95% confidence limits, 0.06 to 0.89) during the first 3 months of the war.

CONCLUSIONS

Consistent with previous observational studies, measles vaccination was associated with a reduction in mortality that cannot be explained by the prevention of measles infection. This nonspecific beneficial effect was particularly strong for girls. Further studies are needed to examine the extent of nonspecific effects in settings with high mortality.

BCG scar and positive tuberculin reaction associated with reduced child mortality in West Africa. A non-specific beneficial effect of BCG?

Previous studies have suggested that the bacille Calmette-Guérin (BCG) vaccine may have a non-specific beneficial effect on childhood survival in areas with high mortality. We examined whether BCG-vaccinated children with a BCG scar or a positive tuberculin reaction had better survival than children without such reactions. As part of an ongoing two-dose measles vaccine trial for which children were recruited at 6 months of age, we examined 1813 children for BCG scar at 6 months of age and 813 BCG-vaccinated children were skin-tested for delayed hypersensitivity to tuberculin, tetanus and diphtheria. We found that BCG-vaccinated children with a BCG scar had significantly lower mortality compared with BCG scar-negative children, the mortality ratio in the first 12 months of follow-up being 0.41 (0.25-0.67). BCG-vaccinated children with a positive tuberculin test had a mortality ratio of 0.45 (0.24-0.85) compared with tuberculin negative children. These results were unchanged by control for potential confounders or using different cut-off points for a tuberculin-positive response. Exclusion of dead children who had HIV antibodies did not modify the estimate (mortality rate (MR)=0.46 (0.23-0.94)). After censoring for tuberculosis (TB) exposure at home, the mortality ratios for having a scar and being tuberculin-positive were 0.46 (0.27-0.79) or 0.42 (0.21-0.84), respectively. Children positive to tetanus or diphtheria in the skin test had the same mortality as children not responding to these vaccine-related antigens. Thus, BCG scar and a positive tuberculin reaction were associated with better survival in early childhood in an area with high mortality. Since nothing similar was found for responders to diphtheria-tetanus-pertussis (DTP) vaccine, and the effect could not be explained by protection against tuberculosis, the effect of BCG vaccination could be due to non-specific immune-stimulation protecting against other infections.

The challenge of improving the efficacy of measles vaccine

Despite a safe and effective measles vaccine, measles still claims an estimated 800,000 lives per year mostly among children in developing countries. This paper deals with strategies to improve vaccine efficacy and prevent unnecessary deaths, including considerations of one dose at 9 months strategy for developing countries, strain of vaccine, potency and number of doses of measles vaccine. After more than 20 years of measles immunisation in the developing world, the epidemiology of measles is radically changed, and the absence of measles epidemics might lead to waning immunity due to less clinical and subclinical infections boosting the antibody level. An increasing proportion of mothers are vaccinated, thus transferring a lower maternal antibody level to their infants who will be susceptible to measles at a younger age. The strategies to limit nosocomial measles infection and spread of measles epidemics are reviewed. Though the measles elimination programmes have been very effective in the Americas, it seems unlikely that they will be equally effective in the rest of the world. Even if eradication should be possible, it might be unwise to stop measles vaccination because the vaccine apparently has beneficial effects and because it would make measles a likely weapon for bio-terrorism. If we are unlikely to get rid of measles and measles vaccine, it might be wise to study further some of the many unanswered questions regarding the long-term effects of measles and measles vaccination.

Routine vaccinations and child survival in a war situation with high mortality: effect of gender

Non-specific effects of vaccination may be different for boys and girls. Due to the sequential administration of vaccines, it is difficult to separate the effect of different vaccines. We tested sex-specific effects of diphtheria, tetanus, pertussis (DTP) and polio vaccines and measles vaccines during the recent war (1998) in Guinea-Bissau when there was no functioning immunisation programme in the country. The study included 1491 children aged 1-17 months in four urban districts in Bissau. Vaccination status had been assessed in the study area in the 3 months before the war. The effect of DTP and polio vaccines was assessed for children who had not received measles vaccine. The effect of measles vaccine was evaluated for children aged 6-17 months. Compared with measles-unvaccinated children, measles-vaccinated children had lower mortality (mortality ratio (MR)=0.44 (95% CI 0.20-1.00)), the difference being marked for girls (0.25 (0.09-0.71)) but not for boys (0.84 (0.26-2.75)) (test of homogeneity, P=0.095). If measles cases were censored in the analysis, the mortality ratio for vaccinated and unvaccinated children was 0.38 (0.16-0.89). DTP and polio-vaccinated children did not have lower mortality than unvaccinated children. The female-male mortality ratio for DTP and polio-vaccinated children was 3.08 (1.11-8.56) and 0.63 (0.28-1.40) for measles-vaccinated children, a significant inversion of the ratios (test of homogeneity, P=0.013). The divergent female-male mortality ratios are unlikely to be explained by a selection bias going in different directions for different vaccines. The reduction associated with measles vaccination was unrelated to prevention against measles infection. Non-specific effects of vaccination should be assessed separately for boys and girls. Taking these effects into consideration may have implications for child mortality patterns in developing countries.

BCG vaccination among West African infants is associated with less anergy to tuberculin and diphtheria-tetanus antigens

To examine risk factors for anergy, delayed-type hypersensitivity was assessed among 884 infants participating in a vaccine trial in Guinea-Bissau. The infants were skin-tested at 7.5 months of age with a panel of seven intradermal antigens. Risk factors for anergy to tuberculin or anergy to both the diphtheria and tetanus antigens were determined in relation to Bacillus Calmette-Guérin (BCG) vaccination, diphtheria-tetanus-pertussis (DTP) vaccination, and measles vaccination. We found sick children to be more anergic to tuberculin and diphtheria-tetanus antigens than healthy children (OR=2.49 (95% confidence interval 1.40-4.55)). There was a higher prevalence of anergy to tuberculin in the rainy season than in the dry season (OR=1.67 (1.25-2.23)). Children who had taken antimalarials within the last week had a higher prevalence of anergy to tuberculin (OR=1.41 (1.02-1.92)). BCG vaccination was significantly associated with less anergy to tuberculin and diphtheria-tetanus antigens (OR=0.42 (0.28-0.63), OR=0.77 (0.60-0.99), respectively). Children vaccinated with BCG before 1 month of age were more anergic to tuberculin than children vaccinated after 1 month (OR=1.61 (1.19-2.19)). DTP vaccination was associated with less anergy to diphtheria-tetanus antigens (OR=0.40 (0.32-0.49)), but not to tuberculin. Children with a positive reaction to tuberculin were less likely to be anergic to diphtheria-tetanus antigens (OR=0.36 (0.26-0.49)) than children with a negative tuberculin reaction. Children who were vaccinated with BCG before they received their last DTP vaccine were less anergic to diphtheria-tetanus antigens (OR=0.40 (0.16-0.88)) than other DTP-vaccinated children. In conclusion, current disease, rainy season, age below 1 month of age at the time of BCG vaccination, and administration of chloroquine or quinimax within the last 7 days were risk factors for anergy to tuberculin among 7.5-month-old infants. BCG vaccination and a positive tuberculin reaction were associated with a lower prevalence of anergy to both tuberculin and diphtheria-tetanus. Thus, BCG vaccination may contribute to better cell-mediated immune responses among infants.

Safety of combination vaccines: perception versus reality

BACKGROUND

Combination vaccines contain multiple antigens to protect against several diseases simultaneously and have simplified the delivery of childhood immunizations. Children are healthier today because of the use of combination vaccines, and the United States is benefiting from record low numbers of vaccine-preventable diseases. Despite obvious benefits, concerns and misconceptions exist regarding the safety and efficacy of combination vaccines.

METHODS

A review of the pediatric literature to dispel the common misperceptions and potential barriers to combining vaccines.

RESULTS

Assurance that combination vaccines approved by the United States Food and Drug Administration undergo extensive testing will help to alleviate concerns regarding safety and efficacy of combination vaccines. Food and Drug Administration standards are rigorous and require that combination vaccines be as safe and effective as each component of the vaccine administered separately. Combination vaccines have been available for >50 years, and lessons learned during this time are continuously applied to the development and use of new products.

CONCLUSIONS

Children will benefit from new combination vaccines because fewer injections will be required to protect against vaccine-preventable diseases, allowing for the introduction of new vaccines into the immunization schedule and prevention of additional diseases.

Present anti-measles immunity in Jordan

The immunity of adults and the prevalence of measles was determined in order to evaluate the adequacy of current measles vaccination policy in Jordan. A total of 307 sera, collected from adults aged 18--40 years, were tested for anti-measles antibodies by ELISA technique. The overall prevalence of anti-measles antibodies was 94.8% and there was no significant difference in the seropositivity rate between males (95.7%) and females (94%). Of the tested adults, 71% were vaccinated and 29% escaped vaccination. In Jordan, measles outbreaks occur periodically and predominantly attack children aged 5--14 years. Our data support introducing the compulsory MMR vaccine in the year 2000 to improve the vaccination coverage of measles; since the optional single dose vaccination has not interrupted the circulation of the measles virus. A second dose of MMR vaccine could be offered to Jordanians either at school entry or at the age of 11--12 years, based on the outcome of the compulsory single dose of MMR vaccine.

Measles antibody responses after early two dose trials in Guinea-Bissau with Edmonston-Zagreb and Schwarz standard-titre measles vaccine: better antibody increase from booster dose of the Edmonston-Zagreb vaccine

In Guinea-Bissau, children were randomised at 6 months of age to receive either two doses of standard-titre measles vaccine at 6 and 9 months of age or an inactivated polio vaccine at 6 months and standard-titre measles vaccine at 9 months of age. During the first 5 months, children received Edmonston-Zagreb (EZ) vaccine and during the following 11 months, the Schwarz (SW) vaccine. Five percent of the mothers, 74% of children at 6 months of age, and 92% of unvaccinated children at 9 months of age had unprotective levels (<125 mIU/ml) of measles antibodies. Among children receiving EZ vaccine, 1% were unprotected at 18 months of age after either two (3/240) or one (3/211) doses of vaccine, the geometric mean measles antibody titre (GMT) being approximately 1550 mIU/ml in both groups. Among those receiving SW vaccine 9% (34/365) and 3% (9/310) were unprotected at 18 months of age in the two-dose and the one-dose groups (RR = 3.21 (95% confidence interval (CI) 1.56-6.58)), respectively. The GMT was higher after one dose of SW vaccine at 9 months of age (2491 mIU/ml) than after two doses of SW vaccine (1125 mIU) (P < 0.001). In the EZ vaccine group, there was no significant difference in antibody level for children vaccinated in the presence of high or low levels of maternal antibodies, whereas there was a marked difference in the SW group. The second EZ vaccine induced a significant antibody increase between 9 months of age (1191 mIU) and 18 months of age (1602 mIU, P=0.011), whereas antibody levels tended to decline from 9 months (1243 mIU) to 18 months of age (998 mIU, P = 0.124) after the second dose of SW vaccine. Conclusively, after two doses of EZ measles vaccine more children were protected at 18 months of age than after two doses of SW. One dose of SW provided the highest antibody response, but a higher proportion of unprotected than one or two doses of EZ. The EZ vaccine was less sensitive to maternal antibodies, and able to increase the antibody response by revaccination, while the second SW vaccine resulted in an unchanged or lower antibody response.

Routine vaccinations and child survival: follow up study in Guinea-Bissau, West Africa

OBJECTIVE

To examine the association between routine childhood vaccinations and survival among infants in Guinea-Bissau.

DESIGN

Follow up study.

PARTICIPANTS

15 351 women and their children born during 1990 and 1996.

SETTING

Rural Guinea-Bissau.

MAIN OUTCOME MEASURES

Infant mortality over six months (between age 0-6 months and 7-13 months for BCG, diphtheria, tetanus, and pertussis, and polio vaccines and between 7-13 months and 14-20 months for measles vaccine).

RESULTS

Mortality was lower in the group vaccinated with any vaccine compared with those not vaccinated, the mortality ratio being 0.74 (95% confidence interval 0.53 to 1.03). After cluster, age, and other vaccines were adjusted for, BCG was associated with significantly lower mortality (0.55 (0.36 to 0.85)). However, recipients of one dose of diphtheria, tetanus, and pertussis or polio vaccines had higher mortality than children who had received none of these vaccines (1.84 (1.10 to 3.10) for diphtheria, tetanus, and pertussis). Recipients of measles vaccine had a mortality ratio of 0.48 (0.27 to 0.87). When deaths from measles were excluded from the analysis the mortality ratio was 0.51 (0.28 to 0.95). Estimates were unchanged by controls for background factors.

CONCLUSIONS

These trends are unlikely to be explained exclusively by selection biases since different vaccines were associated with opposite tendencies. Measles and BCG vaccines may have beneficial effects in addition to protection against measles and tuberculosis.

Placental transfer and decay of maternally acquired antimeasles antibodies in Nigerian children

BACKGROUND

In developing countries vaccination against measles virus (MV) is generally administered at 9 months of age, although it is well-documented that protection of most infants by passively acquired maternal MV antibodies is waning before immunization is given. The purpose of this study was to investigate the decay of maternally derived MV antibodies in Nigerian infants as well as to compare a German and Nigerian cohort of paired mothers and newborns regarding the placental transfer efficiency of MV-specific IgG and total IgG antibodies.

METHODS

MV-specific IgG antibodies were measured with a commercially available MV-enzyme-linked immunosorbent assay, a recombinant hemagglutinin enzyme-linked immunosorbent assay as well as a neutralization assay. Total IgG values were determined with a standard immunoturbidimetric test.

RESULTS

Anti-MV IgG titers were twice as high in German newborns as in Nigerian newborns. An increased concentration of immunoglobulins transferred via the placenta was found only in the German cohort. High concentrations of total maternal IgG reduced the concentration of MV-specific as well as total IgG that crossed the placenta. Furthermore only 17% of the 4-month-old Nigerian infants were still protected against measles. Antibodies had a biologic half-life of 33 days and a biochemical half-life of 48 days.

CONCLUSIONS

Our findings demonstrate that the decay of passively acquired MV antibodies occurred even more rapidly than expected resulting in susceptibility to MV in most of the 4-month-old infants in Nigeria. Furthermore transfer of maternal anti-MV IgG and total IgG antibodies to the newborn was more efficient in the German cohort compared with the Nigerian group. These findings suggest the use of alternative vaccination strategies in developing countries to possibly reduce the window of susceptibility against measles.

Measles elimination: progress and challenges

The accelerating progress in reducing measles incidence and mortality in many parts of the world has led to calls for its global eradication during the next 10-15 years. Three regions have established goals of elimination of indigenous transmission of measles. The strategy used in the Americas of a mass 'catchup' campaign of children 9 months to 15 years of age, high coverage through routine vaccination of infants, intensive surveillance and follow-up campaigns to prevent excessive build-up of susceptibles has had great success in reducing measles transmission close to zero. However, while these developments are impressive, much remains to be done to reduce measles-associated mortality in western and central Africa, where less than half of children are currently receiving measles vaccine and half a million children die from measles each year. The obstacles to global measles eradication are perceived to be predominantly political and financial. There are also technical questions, however. These include the refinement of measles elimination strategies in the light of recent outbreaks in the Americas; the implications of the HIV epidemic for measles elimination, issues around injection safety, and concerns about the possibility that secondary vaccine failures will contribute in sustaining transmission in highly vaccinated populations. The global priorities are to improve measles control in low income countries, increase awareness among industrialized countries of the importance of measles, and conduct studies to answer the technical questions about measles elimination strategies.