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). Mainoutcomemeasure: 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. The trial took place in Guinea-Bissau in the Bandim Health Project’s study area, which covers six districts with approximately 102 000 inhabitants—that is, 30% of the population of the capital Bissau.28 All residents have an identification number in the census files, and information on the place of residence can be retrieved from these files, along with socioeconomic and demographic information. All houses are visited every month to register new pregnancies and births. All children are visited at home every three months until the age of 3 years; at these visits, we collect information on breastfeeding status, infections, hospital admissions, vaccination status, living with the mother, and ownership of pigs. Three health centres in the project area provide routine vaccinations. At the beginning of this trial, the coverage for the third DTP vaccine was 89% and that for measles vaccine was 88% among children aged 12-23 months of age.29 During the trial period from 2003 to 2009, many government driven health intervention campaigns occurred, as is now usual in Guinea-Bissau and other West African countries. We had field assistants who accompanied all the campaign teams in the study area to monitor who received the interventions (table 1​1).). Two measles vaccination campaigns took place in May 2006 and July 2009. With permission from the Ministry of Health, the study participants were excluded from these campaigns (see web table A). Participants in the trial could have taken part in other randomised trials in the area (table 1​1 and web table A).30 31 32 Thus, even though the two dose measles trial was randomised, we needed to examine in subanalyses the effects that these other interventions may have had on the main intervention. Background factors for early two dose measles vaccine (group A) and measles vaccine at 9 months (groups B+C). Values are percentages (numbers) unless stated otherwise DTP= diphtheria-tetanus-pertussis; LBW=low birth weight; OPV=oral polio vaccine; VAS=vitamin A supplementation. *All campaigns in study population were monitored to assess possible interactions; field assistants accompanied all campaign teams in study area. †From 2006 onwards vitamin A supplementation campaigns have included treatment with mebendazole for children aged 1-4 years. The primary objective of this study was to measure the effect of different strains and schedules of measles vaccination on overall mortality between 4.5 and 36 months of age. The sample size was based on the hypothesis that we should be able to measure a 25% difference in mortality between early measles vaccination and the current policy of measles vaccination at 9 months of age. The secondary objectives were to measure mortality between 4.5 and 9 months of age and between 9 and 36 months of age and to determine the possible effect of sex and season. We hypothesised that the non-specific beneficial effects would be strongest for girls and in the dry season. However, we could not power the study to test a significant difference between girls and boys and between dry and rainy seasons. The trial included three arms: two dose measles vaccination providing standard dose Edmonston-Zagreb measles vaccine at 4.5 and 9 months of age (group A), no vaccine at 4.5 months and standard dose Edmonston-Zagreb measles vaccine at 9 months of age (group B), and no vaccine at 4.5 months and standard dose Schwarz measles vaccine at 9 months of age (group C). All children were enrolled and randomised at 4.5 months of age. Because a condition for entering the trial was that the children had received the third DTP vaccine at least four weeks before enrolment, the children in groups B and C had the third DTP vaccine as their most recent vaccination between 4.5 and 9 months of age. We have previously reported the clinical protection of one dose of measles vaccine at 4.5 months of age26; the first dose of measles vaccine at 4.5 months of age was highly protective against clinical measles infection and 100% protective against hospital admission for measles (95% confidence interval 46% to 100%) and death from measles (−42% to 100%). By 24 months of age, all the 925 children tested in the study had responded with specific antibodies to measles vaccination; 97% in group A, 99% in group B, and 99% in group C had protective levels of measles antibodies (unpublished data). The WHO immunisation programme uses standard dose Edmonston-Zagreb and Schwarz measles vaccines interchangeably. However, if vaccines have non-specific effects,11 19 these could differ between two strains of measles vaccine with very different biological qualities, including that Edmonston-Zagreb is more immunogenic than Schwarz in the presence of maternal antibodies.23 We therefore intended to compare the effect on children’s survival of these two strains by comparing groups B and C. We used the early two dose measles vaccination schedule to examine whether effective vaccination at 4.5 months and 9 months of age with long term maintenance of measles antibodies was possible and to study whether measles vaccine compared with the third DTP vaccine had non-specific beneficial effects for child health by comparing group A with groups B and C. We hypothesised that a beneficial effect would be particularly important for girls. We present the results of this analysis here. We called the children in groups B and C for an additional visit at 18 months and randomised them to an additional dose of the same strain of measles vaccine or no additional dose to examine whether the additional dose had an effect on the long term maintenance of measles antibody concentrations. The additional dose had no effect on antibody concentrations (unpublished data). We found no difference in mortality between 18 months and 36 months of age in children who received an additional dose and those who did not (fig 1​1).). We have therefore not further divided the children in group B and C into those who received or did not receive an additional dose of measles vaccine. Fig 1 Trial diagram for early two dose measles vaccination trial. DTP3=third diphtheria-tetanus-pertussis vaccine; EZ=Edmonston-Zagreb vaccine; ITT=intention to treat analysis; MV=measles vaccine; PP=per protocol analysis; VAS=vitamin A supplementation. *Children in groups B and C were randomised to receive or not receive a booster dose of same measles vaccine at 18 months of age; deaths in parenthesis are number of deaths between randomisation at 18 months of age and end of the study; these deaths are included in total for group We based the sample size on the calculation that, with a power of 80%, a significance level of 5%, and an annual mortality rate of 50 per 1000 person years, we needed 4360 person years in each group to detect a 25% difference in mortality from 4.5 to 36 months of age between any two of the three groups. With an expected 10% loss to follow-up and an average follow-up of 30 months, we needed 1918 children in each arm of the study. Owing to additional immunological studies, we enlarged the cohort to include 6648 children. As all children were treated according to the original protocol until 3 years of age, we analysed mortality for the complete cohort. Study procedures have been described in detail in a previous paper.26 We identified newborn infants in the Bandim Health Project registration system and reminded mothers to bring their children for DTP vaccination at 6, 10, and 14 weeks of age. Enrolment in the measles vaccination trial occurred at 4.5 months of age. To facilitate access of the local populations, enrolment was organised by the same team of physician, nurses, and field workers on different weekdays at the three local health centres. The mothers or guardians of children presenting at the local health centre received an oral and a written explanation of the study from a doctor. They were told that which measles vaccine strain or vaccination strategy was best was not known. At each visit to the health centre, the doctor did a medical examination. If they agreed to participate, the mothers or guardians were asked to select an envelope with the allocation number that defined to which group the child belonged. We randomised children to one of three equal sized groups by using block randomisation with 24 envelopes per bag. Block randomisation was organised within the whole study area and not by health centre. Study participants had access to free consultations at the local health centres and to essential drugs free of charge. Children randomised to group A received a standard titre Edmonston-Zagreb vaccine from the Serum Institute of India, Pune, India, at 4.5 and 9 months of age. At 9 months of age, the children in group B received the same Edmonston-Zagreb measles vaccine, and children in group C received a Schwarz measles vaccine (Rouvax) from Pasteur Merieux, France. As described previously, no placebo was given.26 We have previously used inactivated polio vaccine as a control vaccine in trials of early measles vaccination.25 However, inactivated polio vaccine and other inactivated vaccines may increase the female to male mortality ratio,25 so we could not use a control vaccine if we were to measure the non-specific effects of measles vaccine. If we had used a placebo, some mothers in the control group might erroneously have believed that the child had received measles vaccine. As long as they remained in the study area this would matter little, as they would all be called for measles vaccination at 9 months of age. However, if they moved from the area they might not have gone to another health centre to seek measles vaccination. We therefore preferred to use no placebo. Mothers in the control group were told that their children would not receive measles vaccine at enrolment, but that they should receive measles vaccine at 9 months of age. Mortality between 4.5 and 9 months of age—All children were invited back to the health centre at 9 months of age. If the children were not at home or were travelling, we kept calling the children until they were 18 months of age. Mortality between 9 and 36 months of age—All children were invited back to the health centre at 24 months of age, and all children were visited at home after 36 months of age by the Bandim Health Project demographic surveillance system. At these visits we obtained information about whether the children had died or moved: we followed children who moved within the study area to their new address, and we censored children who moved out of the area in the survival analysis at the time of moving. Mothers and their children travel frequently to visit family in the rural areas or to take part in the harvest of cashew nuts. However, information on survival is always available; if a child dies in the rural areas, the family in Bissau is informed immediately. A measles outbreak began during the early phase of the trial in October 2003 and lasted until May 2004. This epidemic was unexpected because Bandim Health Project has kept a very high coverage for measles vaccination for children under 3 years of age for many years in this community.26 However, the coverage of vaccination had generally declined in the city, and many older and presumably unvaccinated children had moved in from rural areas. The epidemic and measles surveillance during the epidemic has been described elsewhere,26 29 and we tested the efficacy of measles vaccine at 4.5 months of age during the epidemic.26 During the study, 110 children were diagnosed as having measles: 71 cases were confirmed by serology, 10 did not have complete serology but were diagnosed as definite measles by clinicians, and 29 were diagnosed by the mother. For this study, we used the data on measles cases to censor for measles infection in the survival analysis to obtain an estimate of the effect of measles vaccine on non-measles related mortality. By censoring all cases of measles at the time of measles infection, we excluded from the comparison not only deaths from acute measles but also potential long term excess mortality after measles infection. We entered data daily. We proofread important variables and assured consistency with the general registration system. We used Stata version 10 for the statistical analyses. For mortality, we present deaths and observation time together with hazard rate ratios and Wald 95% confidence intervals estimated from a Cox proportional hazards model with age as the underlying time variable. P values were calculated from Wald tests. As in previous survival analyses, we label these mortality hazards rate ratios as mortality rate ratios. Using time since inclusion as the underlying time made virtually no difference to the results. We assessed the proportional hazards assumption graphically and tested it by using Schoenfeld residuals (P=0.70). We adjusted for age as inherent in the Cox model and for district by stratification. We used the Kaplan-Meier method to calculate accumulated mortality curves for groups A and B+C, both overall and stratified by birth cohort. In the intention to treat analysis, children were followed from enrolment to 36 months of age or until censoring due to movement or death, irrespective of whether the child received measles vaccine at 9 months of age. In the per protocol analyses, we examined the mortality of all children from enrolment at 4.5 months of age to the 9 month vaccination and mortality between 9 and 36 months of age for the children who received measles vaccine at 9 months of age. As we compared different strains of measles vaccine, we needed to provide the measles vaccine to know what strain had been provided, so we censored children who had received measles vaccine elsewhere. An overall per protocol estimate between 4.5 and 36 months of age came from censoring children not receiving measles vaccine from us at 9 months of age. Hence, the intention to treat and per protocol analyses were the same between 4.5 and 9 months of age; the only difference was that children who did not receive measles vaccine from us at 9 months of age were included in the intention to treat but not in the per protocol analysis from 9 to 36 months of age. In the initial phase of the trial, 80 children had had measles infection before enrolment at 4.5 months of age (five died). Furthermore, the protocol specified that children should be enrolled four weeks after the third DTP vaccination. However, in the first month, a programming error meant that 131 children were enrolled within 25 days of the third DTP vaccination (seven died). Furthermore, we excluded 18 children because they were enrolled twice (none died); this may happen if the child has been registered with two identification numbers because the mother and the father live in different places or because the child often stays with a grandparent; we excluded these children from the study. We excluded two children who had the wrong age recorded; they were both one year older than originally assumed (neither died). As in the previous analysis,26 we excluded these 231 children from the main analysis. A further 17 children received the wrong type of measles vaccine at 9 months of age and they have been censored in the analysis from the date of this vaccination (none died).