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September 2001, Vol. 7, No. 3 Public Health Most people would not question the idea that childhood immunizations increase child survival. Some recent evidence, however, has thrown doubt on this common understanding. To further assess the effects of childhood vaccinations, Population Council researcher Brian Pence, along with Philomena Nyarko and Cornelius Debpuur, postdoctoral research fellows at the Navrongo Health Research Centre in Ghana, examined data collected over five years on immunization and child mortality in Ghana's rural Kassena-Nankana District. The investigators were both surprised and reassured by their findings. For three decades UNICEF has advocated that children in developing countries receive vaccinations against diphtheria, measles, pertussis, poliomyelitis, tetanus, and tuberculosis. Researchers have shown these vaccinations to reduce disease-specific illness and death. Some critics argue, however, that a reduction in deaths from these targeted diseases may not necessarily translate into improved child survival in situations where children are at high risk of death from other causes. Further complicating the picture are recent results from Guinea-Bissau. These findings suggest that the diphtheria, pertussis, and tetanus (DPT) vaccine may increase all-cause child mortality in high-mortality settings. Other evidence, mean-while, suggests that the measles vaccine may confer survival advantages much greater than would be expected given the proportion of deaths caused by the disease. To clarify the effects of childhood vaccinations in high-mortality settings, Nyarko, Pence, and Debpuur analyzed data that had been collected in the Navrongo Demographic Surveillance System (NDSS). In addition to information on births, deaths, migration, marriage, and pregnancies, NDSS interviewers have annually collected data on vaccination status for children less than 2 years of age at the time of first interview. Interviewers record dates of vaccination only if the mother has a health card or other written record of the date and vaccination given. The data used in this study pertain to children born in the study area between 1 October 1994 and 31 December 1999 and for whom information is available in at least one of the vaccination surveys. The sample size was 17,701 children. The investigators considered Bacillus Calmette-Guerin (BCG), polio, and DPT vaccinations as a group, taking note of whether a child received none of them, some of them, or all of them. (It was impossible for them to consider the influence of polio and DPT vaccines separately because these vaccines, which are both given in three rounds, are generally administered at the same time.) The investigators also took into account whether a child received a measles vaccination. Immunization in Kassena-Nankana "This may be attributed to the high proportion of births, almost 60 percent, that occur at home," explains Debpuur. The analysis revealed that children who received no immunizations were at a substantially higher risk of death through approximately the first year of life than were those who received some or all of the recommended vaccinations. Children who received some or all of the BCG/polio/DPT series faced mortality risks approximately one-tenth to one-fourth those of unvaccinated children. Those who received the measles vaccine, whether or not they completed the BCG/polio/DPT series, faced mortality risks approximately half as high as children who did not receive the measles vaccine. Between the ages of 9 months and 59 months, the total reduction in mortality associated with immunization ranged from 25 percent for children with partial BCG/polio/DPT coverage and no measles vaccination, to 70 percent for children with the full complement of recommended vaccinations. "A consistent relationship links increased vaccination with improved survival," says Nyarko. There may be reasons unrelated to vaccination status that could account for the survival discrepancy between vaccinated and unvaccinated children. Children who have never been vaccinated, for example, may be more likely to live farther away from outreach points, which would be likely to put them at higher risk of death during childhood. To the extent possible, however, the researchers took such factors into account and found that they did not affect the results. While the investigators were unable to differentiate between the effects of BCG, polio, and DPT vaccinations, their findings do not lend support to the findings from Guinea-Bissau. "The dramatic reduction in mortality associated with partial or complete BCG/polio/DPT coverage in this population is clearly not consistent with a deleterious effect of DPT offsetting a beneficial effect of BCG," says Pence. In a high-mortality, sub-Saharan African setting with poor infrastructure such as Kassena-Nankana District, success in delivering even part of the UNICEF-recommended package of vaccines can yield substantial health dividends. Source Outside funding | |||||||||||||||||||||||||||||||||||||||||||||||
