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Study of Common Illnesses Before and After Vaccination: A Risk interval Approach
Rajeev Z Kompithra1, Rajiv Sarkar, Leni G Mathew
1Departments of Child Health and *Gastrointestinal Sciences, Christian Medical College, Vellore, Tamil Nadu, India. Correspondence to: Dr Rajeev Z Kompithra, Department of Child Health, Christian Medical College and Hospital, Vellore, Tamil Nadu, India. rajeev.k_zachariah@yahoo.in.
Insights
Most childhood illnesses occur more frequently before routine vaccinations, except for fever. Understanding these background illness rates is crucial for accurately assessing vaccine safety and adverse events.
Area of Science:
- Pediatric medicine
- Immunology
- Public health
Background:
- Assessing vaccine safety requires understanding the background incidence of common childhood illnesses.
- Distinguishing true adverse events from coincident illnesses is a challenge in post-vaccination surveillance.
Purpose of the Study:
- To compare the incidence of illnesses in children during the week before and the week after routine vaccinations.
- To determine the background rates of common childhood illnesses to aid in adverse event assessment.
Main Methods:
- A self-controlled case-series design was employed.
- 1602 healthy infants and children were enrolled at a Well Baby Clinic.
- Interviews were conducted pre- and post-vaccination to record daily illness episodes.
Main Results:
- Except for fever, common childhood illnesses occurred at higher rates before vaccination.
- Fever risk ratios were elevated post-vaccination for both whole-cell and acellular vaccines.
- Gastrointestinal events (diarrhea, vomiting) following rotavirus vaccine showed similar rates pre- and post-immunization.
Conclusions:
- Most reported vaccine adverse events are common childhood illnesses.
- Accurate assessment of causal relationships between vaccines and adverse events necessitates establishing background illness rates.
Objective:
To compare the proportion of children who developed a specified illness in the 7 day post-vaccination window, with the background rate of the same event in the 7 day pre-vaccination window.
Study Design:
Risk interval approach (Self-controlled case-series).
Setting:
Well Baby Clinic of Christian Medical College, Vellore.
Participants:
1602 healthy infants and under-six children presenting for routine vaccination.
Outcome Measures:
Episode of any illness.
Methods:
The interviewer enquired about any adverse event or illness experienced by the child for each day of the week preceding the administration of age-appropriate vaccines. A second interview (telephonic) was conducted by the same interviewer one week following vaccine administration to enquire about adverse event(s) experienced by the child for each day of the subsequent week using a similar protocol.
Results:
With multiple vaccines delivered at appropriate ages, common childhood illnesses that could be reported as adverse events following immunization, except fever (RR=5.7, 95% CI=4.50-7.35), occurred at higher rates pre-vaccination. Risk Ratios of fever following whole cell (RR=9.3, 95% CI=6.43-13.52) and acellular (RR=8.5, 95% CI=3.82-18.91) vaccines were similar, with both showing a decreasing trend with increasing age. The gastrointestinal adverse event profile [diarrhea (RR=0.6, 95% CI=0.14-2.51) and vomiting (RR=1.0, 95% CI=0.14-7.10)] for rotavirus vaccine was similar pre- and post-immunization.
Conclusions:
Since most adverse events to vaccines are also common childhood illnesses, estimating the background rates of common illnesses is important to accurately ascertain a causal relationship.
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