Determinants of measles mortality in a rural area of Guinea-Bissau: crowding, age, and malnutrition

Symptom propagation in respiratory pathogens of public health concern: a review of the evidence

Symptom propagation occurs when the symptom set an individual experiences is correlated with the symptom set of the individual who infected them. Symptom propagation may dramatically affect epidemiological outcomes, potentially causing clusters of severe disease. Conversely, it could result in chains of mild infection, generating widespread immunity with minimal cost to public health. Despite accumulating evidence that symptom propagation occurs for many respiratory pathogens, the underlying mechanisms are not well understood. Here, we conducted a scoping literature review for 14 respiratory pathogens to ascertain the extent of evidence for symptom propagation by two mechanisms: dose-severity relationships and route-severity relationships. We identify considerable heterogeneity between pathogens in the relative importance of the two mechanisms, highlighting the importance of pathogen-specific investigations. For almost all pathogens, including influenza and SARS-CoV-2, we found support for at least one of the two mechanisms. For some pathogens, including influenza, we found convincing evidence that both mechanisms contribute to symptom propagation. Furthermore, infectious disease models traditionally do not include symptom propagation. We summarize the present state of modelling advancements to address the methodological gap. We then investigate a simplified disease outbreak scenario, finding that under strong symptom propagation, isolating mildly infected individuals can have negative epidemiological implications.

Measles vaccination and reduced child mortality: Prevention of immune amnesia or beneficial non-specific effects of measles vaccine?

Measles vaccine (MV) has been observed to reduce all-cause mortality more than explained by prevention of measles infection. Recently, prevention of "measles-induced immune amnesia" (MIA) has been proposed as an explanation for this larger-than-anticipated beneficial effect of measles vaccine (MV). According to the "MIA hypothesis", immune amnesia leads to excess non-measles morbidity and mortality, that may last up to five years after measles infection, but may be prevented by MV. However, the benefits of MV-vaccinated children could also be due to beneficial non-specific effects (NSEs) of MV, reducing the risk of non-measles infections (The "NSE hypothesis"). The epidemiological studies do provide some support for MIA, as exposure to measles infection before 6 months of age causes long-term MIA, and over 6 months of age for 2-3 months. However, in children over 6 months of age, the MIA hypothesis is contradicted by several epidemiological patterns: First, in community studies that adjusted for MV status, children surviving acute measles infection had lower mortality than uninfected controls (44%(95%CI: 0-69%)). Second, in six randomised trials and six observational studies comparing MV-vaccinated and MV-unvaccinated children, the benefit of MV changed minimally from 54%(43-63%) to 49%(37-59%) when measles cases were censored in the survival analysis, making it unlikely that prevention of measles and its long-term consequences explained much of the reduced mortality. Third, several studies conducted in measles-free contexts still showed significantly lower mortality after MV (55%(40-67%)). Fourth, administration of MV in the presence of maternal measles antibody (MatAb) is associated with much stronger beneficial effect for child survival than administration of MV in the absence of MatAb (55%(35-68%) lower mortality). The MIA hypothesis alone cannot explain the strongly beneficial effects of MV on child survival. Conversely, the hypothesis that MV has beneficial non-specific immune training effects is compatible with all available data. Consideration should be given to continuing MV even when measles has been eradicated.

Protection against severe infectious disease in the past

Before the 20th century many deaths in England, and most likely a majority, were caused by infectious diseases. The focus here is on the biggest killers, plague, typhus, smallpox, tuberculosis, cholera, typhoid, dysentery, childhood infections, pneumonia, and influenza. Many other infectious diseases including puerperal fever, relapsing fever, malaria, syphilis, meningitis, tetanus and gangrene caused thousands of deaths. This review of preventive measures, public health interventions and changes in behavior that reduced the risk of severe infections puts the response to recent epidemic challenges in historical perspective. Two new respiratory viruses have recently caused pandemics: an H1N1 influenza virus genetically related to pig viruses, and a bat-derived coronavirus causing COVID-19. Studies of infectious diseases emerging in human populations in recent decades indicate that the majority were zoonotic, and many of the causal pathogens had a wildlife origin. As hunter-gatherers, humans contracted pathogens from other species, and then from domesticated animals and rodents when they began to live in settled communities based on agriculture. In the modern world of large inter-connected urban populations and rapid transport, the risk of global transmission of new infectious diseases is high. Past and recent experience indicates that surveillance, prevention and control of infectious diseases are critical for global health. Effective interventions are required to control activities that risk dangerous pathogens transferring to humans from wild animals and those reared for food.

Developing the concept of beneficial non-specific effect of live vaccines with epidemiological studies

BACKGROUND

Epidemiological and immunological studies are increasingly reporting non-specific effects (NSEs) of vaccines; i.e. vaccines may affect the risk and severity of non-targeted infections. We reviewed how epidemiological studies developed the concept of beneficial NSEs of live vaccines.

SOURCES

This is a personal narrative of how we came to pursue the concept of NSEs in studies of measles vaccine (MV) from the late 1970s. We also searched Pubmed for epidemiological studies of nonspecific/non-specific effects (NSEs) of the most common human vaccines.

CONTENT

When smallpox vaccine was introduced around 1800, bacillus Calmette-Guérin (BCG) against tuberculosis in the 1920s and oral polio vaccine (OPV) in the 1960s, there were suggestions that these live attenuated vaccines reduced mortality more than expected. However, scientific follow-up was limited and the concept of beneficial NSEs did not become mainstream. We observed beneficial NSEs after MV was introduced in low-income countries in the 1970s. Subsequent observational studies and randomized trials confirmed beneficial NSEs of smallpox vaccine, BCG and OPV. Recently, beneficial NSEs have been claimed for the non-live diphtheria-tetanus-pertussis and rabies vaccines. However, no non-live vaccine has yet been documented to produce beneficial NSEs.

IMPLICATIONS

Observational and experimental research has shown beneficial NSEs of four live attenuated vaccines: smallpox vaccine, BCG, OPV and MV. With immunological evidence now supporting the epidemiological observations, it is urgent to take both the specific and NSEs into account in the planning of vaccination programmes.

Non-specific effects of measles, mumps, and rubella (MMR) vaccination in high income setting: population based cohort study in the Netherlands

Objectives To investigate whether measles, mumps, and rubella (MMR) vaccine has positive non-specific effects in a high income setting and to compare rates of hospital admissions for infections between children aged ≤2 years who received live MMR vaccine and those who received an inactivated vaccine against diphtheria, tetanus, pertussis, polio, and Haemophilus influenzae type b (DTaP-IPV-Hib) as their most recent vaccination.Design Nationwide population based cohort study.Setting In the Netherlands, DTaP-IPV-Hib+pneumococcal vaccination (PCV) is recommended at ages 2, 3, 4, and 11 months and MMR + meningococcal C (MenC) vaccination at age 14 months. Data from the national vaccine register were linked to hospital admission data.Participants 1 096 594 children born in 2005-11 who received the first four DTaP-IPV-Hib+PCV vaccines.Main outcome measures Hazard ratio for admission to hospital for infection in children with MMR+MenC compared with the fourth DTaP-IPV-Hib+PCV as their most recent vaccination. Cox regression was performed with most recent vaccination as time dependent variable, adjusted for potential confounders. Analyses were repeated with admission for injuries or poisoning as a negative control outcome. In addition, rate of admission for infection was compared between the fourth and third DTaP-IPV-Hib+PCVas most recent vaccination.Results Having had MMR+MenC as the most recent vaccination was associated with a hazard ratio of 0.62 (95% confidence interval 0.57 to 0.67) for admission to hospital for infection and 0.84 (0.73 to 0.96) for injuries or poisoning, compared with the fourth DTaP-IPV-Hib+PCV as most recent vaccination. The fourth DTaP-IPV-Hib+PCV as most recent vaccination was associated with a hazard ratio of 0.69 (0.63 to 0.76) for admission to hospital for infection, compared with the third DTaP-IPV-Hib+PCV as most recent vaccination.Conclusions Healthy vaccinee bias could at least partly explain the observed lower rate of admission to hospital with infection after MMR vaccination. The lower rate is associated with receipt of any additional vaccine, not specifically MMR vaccine. This emphasises the caution required in the interpretation of findings from observational studies on non-specific effects of vaccination.

Investigation of a measles outbreak in Cordillera, Northern Philippines, 2013

INTRODUCTION

Measles is a highly infectious viral illness that remains one of the leading causes of death among children worldwide. In the Philippines, decreasing routine vaccination coverage from 2007 to 2011 led to local measles outbreaks. A team investigated a measles outbreak reported in Cordillera of the Philippines in May 2013.

METHODS

Measles case data with symptom onset from 2 February to 27 May 2013 were obtained from official sources and verified on site. Data included age, sex, residential address, signs and symptoms and vaccination status. Active case-findings were also conducted for contacts of these cases. The living environments of the cases were investigated. A survey was conducted with the cases and caregivers to understand their knowledge and attitudes about measles.

RESULTS

There were 50 measles cases identified with an age range from six months to 32 years (median: 16 years). Thirty-two were male (64%). Twenty (40%) were hospitalized with one death. Thirty-two (64%) cases were laboratory confirmed, and 36 (72%) received a single dose of measles vaccine. Overcrowded living environments were observed among many cases. The majority of respondents (46/48, 96%) knew about measles, but there were misconceptions about the cause of measles and how it can be prevented and managed.

CONCLUSION

This measles outbreak occurred in an area with low immunization coverage. Achieving 95% measles immunization coverage and strengthening routine immunization strategies to address high-risk populations are recommended. Also, we recommend health education campaigns to include components that address misconceptions about measles.

A randomized trial of a standard dose of Edmonston-Zagreb measles vaccine given at 4.5 months of age: effect on total hospital admissions

Observational studies and trials from low-income countries indicate that measles vaccine has beneficial nonspecific effects, protecting against non-measles-related mortality. It is not known whether measles vaccine protects against hospital admissions. Between 2003 and 2007, 6417 children who had received the third dose of diphtheria, tetanus, and pertussis vaccine were randomly assigned to receive measles vaccine at 4.5 months or no measles vaccine; all children were offered measles vaccine at 9 months of age. Using hospital admission data from the national pediatric ward in Bissau, Guinea-Bissau, we compared admission rates between enrollment and the 9-month vaccination in Cox models, providing admission hazard rate ratios (HRRs) for measles vaccine versus no measles vaccine. All analyses were conducted stratified by sex and reception of neonatal vitamin A supplementation (NVAS). Before enrollment the 2 groups had similar admission rates. Following enrollment, the measles vaccine group had an admission HRR of 0.70 (95% confidence interval [CI], .52-.95), with a ratio of 0.53 (95% CI, .32-.86) for girls and 0.86 (95% CI, .58-1.26) for boys. For children who had not received NVAS, the admission HRR was 0.53 (95% CI, .34-.84), with an effect of 0.30 (95% CI, .13-.70) for girls and 0.73 (95% CI, .42-1.28) for boys (P = .08, interaction test). The reduction in admissions was separately significant for measles infection (admission HRR, 0 [95% CI, 0-.24]) and respiratory infections (admission HRR, 0.37 [95% CI, .16-.89]). Early measles vaccine may have major benefits for infant morbidity patterns and healthcare costs. Clinical trials registration NCT00168558.

The epidemiological and clinical characteristics of measles in Wenzhou, China, 2000-2010

This study examined the epidemiological and clinical characteristics of measles in Wenzhou, China. From 2000 to 2010, a total of 13271 measles cases were reported in Wenzhou, with epidemics occurring every 3-4 years. Forty-five per cent of the cases were aged <1 year and 27.2% were aged >14 years. Of 2262 hospitalized measles cases, 66.3% were diagnosed with pneumonia, and three cases died from respiratory failure. The number of measles cases of infants requiring hospitalization increased from birth to age 8 months and declined thereafter. Measurement of serum measles antibody levels in normal infants indicates that over 80% of infants in Wenzhou may be susceptible to measles by age 6 months. The existence of a sufficient pool of unvaccinated children and the decreased level of passively transferred measles antibodies in infants from vaccinated mothers contributed to the sustained transmission observed in Wenzhou.

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.

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.

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.

Is susceptibility to severe infection in low-income countries inherited or acquired?

From a low-income country perspective, we need to emphasize factors which affect acquired susceptibility to severe infection. Such factors may lend themselves to modification by public health interventions. The present paper reviews the experience with understanding the causes of severe measles infection and the impact of health interventions in Guinea-Bissau over a 28-year period. In the 1970s, acquired susceptibility because of malnutrition was considered to be the main cause of high mortality. However, we found no association between nutritional status and subsequent risk of dying of measles. Instead, crowding and intensity of exposure were the main determinants of severe measles. Factors related to transmission have been substantiated for measles, chickenpox, whooping cough and polio. We found measles vaccination to be associated with a major reduction in mortality, particularly for girls. This suggested that measles vaccine has a beneficial nontargeted immune stimulatory effect. The importance of nontargeted effects was clearly documented when World Health Organization introduced a new high-titre measles vaccine (HTMV). HTMV was fully protective but associated with twofold higher mortality for girls. Bacille Calmette Guérin (BCG), diphtheria-tetanus-pertussis (DTP) and oral polio vaccine (OPV) have also shown nontargeted effects, the effect being beneficial for BCG and OPV but negative for DTP. Both beneficial and negative effects are strongest for girls. There are many acquired factors, which affect susceptibility to infection in ways which have not been explored by medical science. They may have a major impact on child survival in low-income countries.

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.

Ex vivo analysis of cytotoxic T lymphocytes to measles antigens during infection and after vaccination in Gambian children

The study of cytotoxic T cell responses to measles antigens during infection and after vaccination may provide insight into the immunopathology of the infection. It will also provide a knowledge of the immunity conferred by wild or attenuated virus, which will help in the design of new vaccines. Direct cytotoxic T cell responses, which did not require in vitro restimulation, were measured from peripheral blood by a standard 51Cr-release assay in 35 patients with acute measles, using HLA class I matched allogeneic B cells as targets. 77% showed specific responses to measles fusion protein, 69% to the hemagglutinin, and 50% to the nucleoprotein. These responses, which were related to severity of disease and history of previous vaccination, had waned by 14-24 wk after measles when memory responses to the same antigens could be elicited by restimulation in 71% of the 13 patients tested. A similar pattern followed vaccination: direct cytotoxic responses to fusion and hemagglutinin proteins were shown in 70% of the 20 children tested while 50% responded to the nucleoprotein. These responses, which were mediated by both CD8(+) and CD4(+) cells, faded over 6 wk when memory responses could be restimulated. Thus, a vigorous cytotoxic T lymphocyte response to fusion, hemagglutinin, and nucleoproteins is important in both natural and vaccine-induced immunity to measles.

Coinfection is common in measles-associated pneumonia

BACKGROUND

Measles continues to be a significant health problem in developing countries.

OBJECTIVES

To describe the clinical features of measles-associated pneumonia (MAP) and to identify other pathogens involved.

METHODS

Measles diagnosis was ascertained either by the typical symptom complex or by a sensitive enzyme immunoassay for antibody among children < 5 years of age admitted to the hospital with pneumonia. Other pathogens were identified by blood culture, virus isolation or antigen detection from nasopharyngeal aspirate and antibody determination from serum.

RESULTS

Of 182 MAP cases 162 (89%) had clinically typical measles. Twenty patients had a diagnostic antibody finding with an atypical clinical presentation. Thirteen percent were younger than 9 months of age. The case fatality rate was 17%, with a significantly increased odds ratio (OR) for those with cyanosis [OR 4.6, 95% confidence interval (CI) 1.7 to 13], respiratory rate > or = 60/min (OR 3, 95% CI 1.3 to 7) or fulfilling criteria for very severe pneumonia (OR 5.3, 95% CI 2.3 to 12). Mixed infection was found in 53% of patients. Blood culture was positive in 10 patients, Streptococcus pneumoniae (N = 5) being the most common finding. Adenovirus (19%) and parainfluenza (25%) viruses were the most frequent other viruses. A dense infiltrate was seen significantly more often among measles patients with bacterial coinfection (87.5%) than those with other viruses (36%, P = 0.007) or no evidence of other infection (33%, P = 0.004).

CONCLUSION

In MAP, coinfection with other microbes is common. Cyanosis and a respiratory rate of > or = 60/min predict a greater risk of dying.

Non-specific beneficial effect of measles immunisation: analysis of mortality studies from developing countries

OBJECTIVE

To examine whether the reduction in mortality after standard titre measles immunisation in developing countries can be explained simply by the prevention of acute measles and its long term consequences.

DESIGN

An analysis of all studies comparing mortality of unimmunised children and children immunised with standard titre measles vaccine in developing countries.

STUDIES

10 cohort and two case-control studies from Bangladesh, Benin, Burundi, Guinea-Bissau, Haiti, Senegal, and Zaire.

MAIN OUTCOME MEASURES

Protective efficacy of standard titre measles immunisation against all cause mortality. Extent to which difference in mortality between immunised and unimmunised children could be explained by prevention of measles disease.

RESULTS

Protective efficacy against death after measles immunisation ranged from 30% to 86%. Efficacy was highest in the studies with short follow up and when children were immunised in infancy (range 44-100%). Vaccine efficacy against death was much greater than the proportion of deaths attributed to acute measles disease. In four studies from Guinea-Bissau, Senegal, and Burundi vaccine efficacy against death remained almost unchanged when cases of measles were excluded from the analysis. Diphtheria-tetanus-pertussis and polio vaccinations were not associated with reduction in mortality.

CONCLUSION

These observations suggest that standard titre measles vaccine may confer a beneficial effect which is unrelated to the specific protection against measles disease.

Reduced childhood mortality after standard measles vaccination at 4-8 months compared with 9-11 months of age

OBJECTIVE

To evaluate the impact on mortality of standard Schwarz measles immunisation before 9 months of age.

DESIGN

Children vaccinated in 1980-3 at 4-5, 6-8, and 9-11 months of age were followed to migration, death, or the age of 5 years.

SETTING

One urban district and nine villages in two rural areas of Guinea-Bissau.

SUBJECT

307 children vaccinated at 4-8 months and 256 at 9-11 months.

MAIN OUTCOME MEASURES

Mortality from 9 months to 5 years of age for children immunised at 4-5, 6-8, and 9-11 months.

RESULTS

Mortality was significantly lower in children vaccinated at 6-8 months than at 9-11 months (mortality ratio = 0.63, (95% confidence interval 0.41 to 0.97), p = 0.047). As vaccination was provided in semiannual or annual campaigns it is unlikely that age at vaccination reflected a selection bias. The trend was the same in all three study areas. Improved survival after early immunisation was not related to better protection against measles infection. With a Cox multivariate regression model to adjust for age, sex, season at risk, season at birth, measles infection, and region, children vaccinated at 4-8 months had a mortality ratio of 0.61 (0.40 to 0.92, p = 0.020) compared with children vaccinated at 9-11 months. Reimmunised children tended to have lower mortality than children who received only one vaccine (0.59 (0.28 to 1.27, p = 0.176)).

CONCLUSION

Standard measles vaccination before 9 months is not associated with higher childhood mortality than is the currently recommended strategy of immunising from 9 months, and it may reduce mortality. This has implications for measles immunisation strategy in developing countries.

Siblings of opposite sex as a risk factor for child mortality

OBJECTIVE

To examine whether contracting an infection from a sibling of the opposite sex affects child mortality.

DESIGN

Retrospective study of twins and case-control study of randomly selected children conducted within a prospective cohort study.

SETTING

Urban and rural areas of Guinea-Bissau.

SUBJECTS

251 Pairs of twins (65 male pairs, 72 female pairs, and 114 mixed pairs), and 39 children who died and 78 controls identified in a cohort of 853 children aged less than 4, comprising 772 randomly selected children, all twins, and all children who had measles living in Bandim 2.

MAIN OUTCOME MEASURES

Death of a child and sex of cotwin or older sibling nearest in age.

RESULTS

The mortality among children from mixed pairs of twins was higher than that among pairs of the same sex (relative risk 1.47, 95% confidence interval 1.14 to 1.90). Boys had a slightly higher mortality especially in the older groups. In the case-control study the older sibling nearest in age was of the opposite sex for 29 (74%) of the children compared with 36 (46%) of the controls matched for age, sex, and area. Mortality was higher among both boys and girls with older siblings of the opposite sex than among those with siblings of the same sex (odds ratio 1.90, 0.78 to 4.61 v 7.5, 1.59 to 35.30), but the difference was more pronounced among girls.

CONCLUSIONS

Children whose older sibling nearest in age is of the opposite sex or who have cotwins of the opposite sex have a higher mortality from infectious diseases. Further investigation is needed to determine the nature of this relation.

Vaccine-preventable disease and immunization in the developing world

Vaccines have given health care providers control over a substantial portion of the morbidity and mortality in the developing world. Global efforts have immunized two-thirds of the world's children with DTP and polio vaccines; 72% have received BCG and 59% measles vaccine; but only 29% of pregnant women have received two doses of tetanus toxoid. In addition, vaccines against yellow fever, Japanese encephalitis, hepatitis B, rubella, and mumps and meningococcal polysaccharide vaccine are being used in specific regions of the world. New vaccine candidates will enhance the vaccine armamentarium over the next decade to include the causes of pneumonia, diarrhea, and meningitis: Haemophilus influenzae type b, pneumococcal and meningococcal protein conjugate vaccines, typhoid and rotavirus vaccine. Genetically engineered vaccine vehicles, genetic reassortants, and genetic deletions are being investigated as new vaccine candidates.

Decline in measles mortality: nutrition, age at infection, or exposure?

The mortality from measles was studied in an urban area of Guinea-Bissau one year before and five years after the introduction of a vaccination programme. The years after the introduction of immunisation saw a decline in mortality among unvaccinated children with measles. This decline occurred despite a lower age at infection and an increasing prevalence of malnourished children. State of nutrition (weight for age) did not affect the outcome of measles infection. The incidence of isolated cases, however, increased in the period after the introduction of measles vaccination. As mortality was lower among these cases, diminished clustering explained some of the reduction in mortality. Comparison between the urban district and a rural area inhabited by the same ethnic group showed a lower age at infection, less clustering of cases, and lower case fatality ratios in the urban area. Endemic transmission of measles in urban districts leads to less clustering of cases, which may help explain the usually lower case fatality ratios in these areas. As measles vaccination increases herd immunity and diminishes clustering of cases, it may reduce mortality even among unvaccinated children who contract the disease.

Measles in developing countries. Part I. Epidemiological parameters and patterns

This paper presents a review of published data concerning the epidemiology of measles in developing countries. Simple mathematical models provide a framework for data analysis and interpretation. The analyses highlight differences and similarities in the patterns of transmission of the measles virus in developed and developing countries. Whilst the rate of loss of maternally derived immunity to measles is broadly similar, the average age at infection is much lower, and case fatality rates are much higher in developing countries. Data analysis also serves to illustrate inter-relationships between different kinds of epidemiological data. Thus, for example, in order to correctly interpret an age stratified serological profile from a developing country it is necessary to have information on the rate of decay of maternal antibodies and age specific case fatality rates. To determine the probable impact of a given vaccination programme, information on the birth rate in the community concerned is also required. A discussion is given of the epidemiological data required in order to effectively design a community based vaccination programme aimed at the eradication of measles.

Vitamin A supplements and mortality related to measles: a randomised clinical trial

One hundred and eighty children admitted with measles were randomly allocated to receive routine treatment alone or with additional large doses of vitamin A (200,000 IU orally immediately and again the next day). Baseline characteristics of the two groups were virtually identical for age, severity of measles, and vitamin A and general nutritional states. In 91% of the children serum vitamin A concentrations were less than 0.56 mumol/l. Of the 88 subjects given vitamin A supplements, six (7%) died; of the 92 controls, 12 (13%) died (p = 0.13). This difference in mortality was most obvious for children aged under 2 years (one death out of 46 children receiving supplements versus seven deaths out of 42 controls; p less than 0.05) and for cases complicated by croup or laryngotracheobronchitis. Mortality was several times higher in marasmic than in better nourished children, regardless of study allocation (p less than 0.01).

High measles mortality in infancy related to intensity of exposure

In a West African urban community, measles infection in infants was examined over 5 years (1979-1983). In the age group 0 to 11 months, measles mortality was higher among secondary cases (infected in the house) than among index cases (infected outside the house), and the proportion of secondary cases was significantly higher for this age group than for older children. Intensive exposure related to the social pattern of disease transmission may be important in explaining the high infant mortality observed with measles in developing countries. Mortality during the first 12 months of life increased with age, presumably because of the decrease of maternally derived measles antibodies. In children younger than 6 months of age, who are usually considered to be protected by maternal antibody, intensive exposure may lead to infection, as demonstrated by a high level of measles-specific antibodies in some children exposed to an older sibling with measles. The aim of public health policies should be to change conditions of exposure.

Severe measles: a reappraisal of the role of nutrition, overcrowding and virus dose

The factors predisposing to severe measles, which accounts for a considerable fraction of the high infant and child mortality in the third world, are re-examined. The conviction that protein-energy-malnutrition (PEM) aggravates measles is challenged by findings of prospective community-based studies. It was found that severe measles was not associated with PEM but frequently accompanied overcrowding in Guinea-Bissau. Secondary cases fared worse than index patients. Among adequately nourished hospitalised African children, immunological and radiological parameters, together with the effects of age and HLA antigens, were closely related to sickness and death in measles. This variation in case fatality rate does not appear to be simply explained by age-dependent host reactions or differences in medical care. The hypothesis which fits most of the observed facts postulates that the transmission of a large inoculum of virus particles to susceptible children is an important cause of severe disease. The implication of this interpretation is that specific measles control, and not only improvements in nutrition, is important in high risk areas for a reduction of measles mortality. It is further suggested that health policy should promote those social changes which limit intense exposure to measles virus.

Introduction of measles into a highly immunised West African community: the role of health care institutions

In an urban area of Guinea-Bissau, where more than 80% of the children have been vaccinated, measles continues to be a major cause of child mortality. Compared with the period before the introduction of vaccination, more cases occur outside the community, while more cases within the district are now guests and newcomers. Half of the new introductions of measles into the community and 30% of the measles deaths can be traced back to the paediatric ward. Contact with health care institutions plays an important role in the transmission of measles, particularly among the youngest children. This consequence of health care may be avoidable, however, since several studies suggest that sick children can be vaccinated safely and effectively.