Evaluation of a measles-smallpox vaccination campaign by a sero-epidemiologic method
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A new method assessed measles-smallpox vaccination effectiveness in Ivory Coast. Smallpox scars accurately indicated successful measles vaccination coverage and immune response in children.
Area of Science:
- Public Health
- Epidemiology
- Vaccinology
Background:
- Measles and smallpox vaccination programs are crucial for child survival.
- Assessing vaccination coverage and immunologic response is vital for program evaluation.
- Reliable indicators are needed to determine the effectiveness of vaccination campaigns.
Purpose of the Study:
- To devise and evaluate an assessment technique for measles-smallpox vaccination coverage and immunologic status.
- To determine the effectiveness of a measles-smallpox vaccination program in rural Ivory Coast.
- To identify reliable clinical markers for vaccination coverage and immune response.
Main Methods:
- A cohort of 1762 children (0-72 months) in 30 sites were visited thrice: pre-vaccination, within 3 days post-vaccination, and 1 month later.
- Vaccination coverage was assessed via house visits and vaccination scar inspection.
- Immunologic status was determined by measles hemagglutination-inhibition antibody titers from filter paper blood samples and smallpox vaccination major reaction rates.
Main Results:
- Vaccination coverage in the target age group (6-24 months) was 53.6%, significantly higher than outside the target group (10.5%).
- Prior to vaccination, 94.6% of target-age children were susceptible to measles.
- Post-vaccination, seroconversion rates were high: 84.3% in 6-8 month olds and 94.7% in 9-24 month olds.
- A smallpox vaccination scar was the most reliable indicator of recent vaccination and subsequent measles seroconversion (91.4%).
Conclusions:
- The developed assessment technique effectively measures vaccination coverage and immunologic response.
- Smallpox vaccination scars serve as a valuable and reliable clinical marker for assessing measles vaccine effectiveness.
- Targeted vaccination strategies are essential for maximizing coverage in priority age groups.
Abstract:
An assessment technique has been devised whereby children from 30 randomly chosen sampling sites are visited within three days of measles-smallpox vaccination and one month later. Vaccination coverage is measured at house visits and immunologic status is determined by collection of early and late blood samples on filter papers from substratified children in priority age-groups, and by looking at vaccination scars. The methodology was employed in a rural area of the Ivory Coast during the maintenance phase of a measles-smallpox vaccination program; 1762 children from 0--72 months old were inspected. Children in the target age groups, 6--24 months, had a vaccination coverage of 53.6% whereas children outside of the target group had a 10.5% coverage. Of 571 target age children, 94.6% had a measles hemagglutination-inhibition antibody titer of less than 1:10 dilution at the first visit, and were presumed susceptible to measles or vaccine. Of 247 substratified children 6--8 months, 98.3% were susceptible to measles before vaccination; 84.3% of 127 vaccinated children in this age-group sero-converted when re-tested. Of 324 children 9--24 months, 91.7% were susceptible before the campaign; 94.7% of 170 vaccinated children in this age-group converted. A positive history of prior measles or prior measles-vaccination was not a good indicator of measles serologic status. The smallpox vaccination major reaction rate was 93.2%; 91.4% of children with a recent vaccination scar sero-converted to measles vaccine. Thus, the smallpox scar read at the second visit proved the best clinical marker for determining both coverage and immunologic effectiveness of the campaign.