| Study design |
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| Ecological |
Relatively simple and less expensive Allows assessment of the vaccination program in a general population |
Cannot establish causal relationships It is important to consider adjustment for secular trends and to have a control group (other areas without vaccination programs or other diseases) |
| Cohort |
Provides the best information about causal relationships |
Demands more time and resources |
| Descriptive and case series |
Simplest study designs Can detect changes in types of rotavirus and pneumococcus after the introduction of vaccine programs |
Cannot measure prevalence or incidence due to the lack of a well-defined population at risk. Give little information about temporal changes in the frequency of diseases |
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| Data sources |
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| Health information system databases |
Broad coverage, lower costs, easy access to data and longitudinal follow-up |
Lack of standardization in data collection and limitations in completeness and reliability of the available data, database continuity, coverage, representativeness, and sustainability |
| Sentinel-based and laboratory-based surveillance systems |
Availability of unpublished data |
Information on the catchment population frequently unavailable. Data not generalizable for the entire population. Variable coverage |
| Local secondary data (medical records of a single hospital) |
Timeliness, low costs, and availability |
Lack of standardization; data not generalizable to the entire population |
| Primary data |
May answer specific research objectives More precision and reliability |
Small sample size Not generalizable Expensive Sustainability |
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| Clinical syndrome |
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| All-cause diarrhea |
Does not require specific laboratory tests. May be more valuable to decision makers |
Less precision for vaccine effect on rotavirus disease |
| Rotavirus-related diarrhea |
More specific and precise |
May underestimate the true burden of disease and the global impact of vaccination programs |
| Pneumonia |
More frequent |
Challenging and variable definition and diagnosis |
| Invasive pneumococcal disease |
More severe and of more precise diagnosis |
Diagnosis requires the isolation of S. pneumonia, and laboratory tests are not uniformly performed |
| Meningitis |
More severe, of more precise diagnosis and has more information available since it is a notifiable disease |
Less frequent |
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| Outcomes of interest |
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| Hospitalization rate |
Availability of data |
Changes in diagnosis coding may affect estimates. Influenced by availability of beds, hospital admission policies and social factors. Unsuitable for clinical syndromes that are mostly treated in outpatient care such as otitis media |
| Mortality rate |
More reliable than morbidity data |
Measures only results of severe clinical syndromes; thus, changes in less severe conditions will not be identified. Difficulty in discriminating effects of changes in the incidence or treatment of conditions |
