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Presented at a lecture for Clinical Research Coordinators held at King Fahad Medical City on Sunday June 11, 2020, 14.00-13.00 By Professor Omar Hasan Kasule MB ChB (MUK), MPH (Harvard), DrPH (Harvard) Chairman of the Institutional Review Board
TYPES OF DISEASE PREVENTION
• Primary prevention: prevention of initial contact and/or infection by elimination of the source (inactivating the agent, prevention of transmission, and raising the immunological status of the potential host)
• Secondary prevention: early detection and treatment of disease to prevent complications
• Tertiary prevention: prevention of further complications by rehabilitation
• Immunization is a form of primary prevention aimed at increasing host immune resistance by use of specific immunobiology (active and passive immunization)
OBJECTIVES OF IMMUNIZATION
• Bacterial and viral diseases are generally immunizable whereas fungal and protozoal diseases are not. The HPV vaccine against the papillomavirus prevents cancer.
• The goal of immunization is eradicating the disease. More modest objectives are regional elimination of disease or control of disease by reducing morbidity and mortality.
• Immunization leads to both individual protection and an increase of herd immunity.
• The minimum proportion of the population that must be immunized in order to achieve herd immunity is given by 1 – 1/R0 where R0 = basic reproductive rate.
• Large-scale vaccination programs result in an upward shift of the average age at infection due to the decrease in the proportion of the susceptibles being infected.
TYPES OF IMMUNIZATION
• In active immunization a vaccine is given to stimulate antibody production. The vaccines are in the form of live attenuated, Dead/inactivated, Active components, and toxoids (detoxified toxin). The primary IgM antibody response is seen in 1-3 weeks. The secondary IgG antibody response appears later but is permanent.
• In passive immunization an already-formed antibody is infused.
OBJECTIVES OF FIELD IMMUNIZATION SURVEYS
• Assessing the need for vaccination by analyzing morbidity and mortality data,
• Assessing feasibility
• Pre-licence and post-license monitoring,
• Assessing vaccine efficacy by use of specific parameters,
• Monitoring side effects of vaccines including the common and rare ones,
• Assessing uptake and implementation of vaccination programs,
• Evaluation of factors affecting vaccination programs,
• Costing studies
ASSESSMENT OF VACCINE EFFECTIVENESS
• Vaccine effectiveness (VE) is measured as the differences in attack rates in the vaccinated and unvaccinated expressed as a proportion of the total number of the attack rate in the unvaccinated
• VE = (Incidence rate in unvaccinated – incidence rate among the vaccinated) / incidence rate in unvaccinated
• VE= 1 - RR.
PROCESS OF FIELD SURVEYS: PARAMETERS USED
• Disease incidence rates
• Immunological testing eg tuberculin test,
• Seroconversion
• Sero-prevalence.
PROCESS OF FIELD SURVEYS: STUDY DESIGNS
• Community randomized,
• Case-control studies
• Follow-up studies
• Serological surveys to assess vaccination effectiveness
SUCCESS/FAILURE OF VACCINATION PROGRAMS
• Lack of change in disease rates
• Decreasing/increasing disease rates
• Occurrence of disease in the vaccinated.
ADVERSE REACTIONS IN VACCINATION
• Immunization carries with it a relatively low risk of adverse reactions heavily outweighed by the disease preventive benefits.
• The rates of various adverse reactions to BCG vaccination are: disseminated infection <0.1 per 100,000; osteomyelitis <0.1-30 per 100,000; and suppurative adenitis 100-4000 per 100,000. The rates of various adverse effects to DPT immuniization are convulsions 0.3-90 per 100,000; encephalitis 0.1-3 per 100,000; brain damage 02.-0.6 per 100,000; and death 0.2 per 100,000.
ASSESSING VACCINATION COVERAGE WHO METHODOLOGY: PLAN THE SURVEY
• Planning based on the national immunization schedule
• Select the age group of children to be evaluated
• Decide which sources of information to use
• Decide how many interviewers are needed and the length of the survey
• Identify clusters
ASSESSING VACCINATION COVERAGE WHO METHODOLOGY: CONDUCT THE SURVEY
• Select the starting household
• Select subsequent houses
• Complete the cluster forms
• Implement a control system on data collection
ASSESSING VACCINATION COVERAGE WHO METHODOLOGY: TABULATE THE DATA
• Complete the cluster forms
• Complete the summary forms
ASSESSING VACCINATION COVERAGE WHO METHODOLOGY: ANALYZE THE DATA
• Evaluate infant immunization
• Evaluate the reasons for immunization failure
• Evaluate TT immunization of women
DEFINITION OF TERMS
• Cluster: A small group that is part of a population that is being surveyed; for the purposes of evaluating immunization coverage, a cluster is defined as seven or more children in the age range being evaluated.
• Cluster survey: A special study designed to measure the percentage of individuals in a given age group who are immunized.
• EPI (WHO) cluster sampling technique: A survey done in 30 systematically selected clusters of seven or more children to estimate the immunization coverage of all the children that live in the area (i.e. the population) being surveyed.
• Immunization coverage: Proportion of individuals in the target population who are immunized.
• Immunization coverage target: A goal that is prepared for a health facility that states what proportion of individuals in the target population will be immunized with specific vaccines in a given time period.
• Morbidity: Sickness.
• Mortality: Death. Random number: A number selected by chance. Target population: Group of individuals who are included in the immunization services based on their age and the area in which they live.