The Surveillance of Influenza Vaccine Uptake in South Australia, 1993 - 2001
Bernadette Kenny, Anne Taylor, Ann Kempe, Tiffany Gill
Public Health Importance of Influenza
An acute viral disease of the respiratory tract which derives its importance from:
• the rapidity with which epidemics evolve. • the considerable morbidity and mortality associated with complications of Influenza.
Influenza - “At Risk” Population
During major epidemics, severe illness and death occur, primarily among the elderly and those debilitated by chronic cardiac, pulmonary, renal or metabolic disease.
Influenza - Preventive Measures
Administration of inactivated influenza vaccine to individuals at risk of complications is the single most important measure in preventing or attenuating influenza infection and preventing mortality during epidemics.
NHMRC Influenza Vaccination Recommendations
1.Individuals at increased risk of influenzarelated complications. 2.Individuals who can transmit influenza to persons at increased risk 3.Others - wanting to reduce likelihood of becoming ill with influenza for social / economic / individual reasons.
Individuals at increased risk of influenza-related complications.
• Individuals 65 years & over . • Aboriginal & TSI adults 50 years & over . • Adults & children (>6 months) with chronic disorders of the pulmonary or circulatory system • Adults and children (> 6 months) with other chronic illness requiring regular medical follow-up or hospitalisation in the preceding year. • Nursing home / long-term care residents. • Children/ teenagers on long term Aspirin therapy (risk of Reyes syndrome)
Commonwealth Funded Influenza Vaccination
Free Influenza vaccine is available for: • Individuals 65 years or over • Aboriginal & TSI adults 50 years and over . • Aboriginal and Torres Strait Island adults aged 15 to 49 years with chronic illness - in particular, disorders of the pulmonary or circulatory system
The Uptake of Influenza Vaccine in South Australia.
Monitored by the South Australian Communicable Disease Control Branch using the services of the Centre for Population Studies in Epidemiology (CPSE) since 1993.
Influenza Vaccine Uptake Surveillance - Methodology
• 1993 - 1996 Health Omnibus Survey - annual, “door to door” survey. • 1997 - 2001 SERCIS (Social Environmental Risk Context Information System) - telephone survey system.
Health Omnibus Survey
• Annual “door to door” survey.
(HOS)
• Sample size = 4,400 households (3000 completed interviews - minimum) • Sample frame - Metropolitan Adelaide and major country towns (pop >1000) • Clustered, multi-stage, systematic, selfweighting area sample
HOS- Sampling Procedure
• Clustered - ABS Collection Districts (CDs) are basis of sample frame - some, not all, included. • Multi-stage – Stage 1 - Selection of CDs - 340 Metro, 100 country – Stage 2 - Selection of households within CDs - 10 households per CD. – Stage 3 - Selection of individuals within households - aged 15 years or over.
HOS- Sampling Procedure (continued)
• Systematic – Even spread of households across the population - result of systematic sampling of CDs and household. • Self-weighting – Every household within the 2 strata (Metro & country) has same probability of being selected.
SERCIS Surveys
• Computer Aided Telephone Interviewing (CATI) System. • Sample size - flexible, typically 3000 households. • Sampling Procedure Households - random, from EWP. Individuals - aged 18 years or over.
Summary of Survey Instruments
HOS Survey type Sample size Sampling Procedure “door to door” 4400 Clustered, multi-stage, systematic, self-weighting 15+ years SERCIS CATI Typically 3000 random
Interviewee
18+years
Advantages of CATI System
(over “door to door” survey)
Telephone Surveys - low cost, timely, include remote areas. CATI Systems • Perform routine admin functions. • Handle different question types. • Reduce question completion / sequencing errors. • Perform data consistency checks. • Reduce transcription errors. • Provide readily available data. • Can randomly rotate question response categories.
Comparability of Data obtained from HOS and SERCIS
Taylor A W, Wilson D H and Wakefield M. “Differences in health Estimates using telephone and door-to-door survey methods – a hypothetical exercise”. ANZJPH Vol 22, No 2, pp 223-226 Health estimates obtained using EWP sampling are not statistically different from those obtained using a clustered, multi-stage, systematic, selfweighting sampling technique when the sample size is fairly large and the data are appropriately weighted.
South Australians, aged 65 years and over, having an influenza vaccine in the last 12 months
90 80 70 60 50 40 30 20 10 0 1993 1994 1995 1996
%
DOOR-TO-DOOR (HOS)
CATI (SERCIS)
1997
1998
1999
2000
2001
Year of survey
National Influenza Survey, 2000
• CATI survey of vaccine uptake across Australia • Evaluation of Influenza Immunisation coverage achieved via Commonwealth Department of Aged Care Influenza Vaccine Program for Older Australians • Total interviews = 10505 • Analysis - Australia overall & individual state & territory estimates.
National Influenza Survey Coverage
Persons 65 years and over • 74% (CI 73-75%) reported vaccination during 2000. (95% cost free) • Influenza coverage increased 1998 - 2000 14% 1999 - 2000 5% • 57% (CI 56-59%) immunised annually, between 1998 – 2000.
National Influenza Survey Perceptions
Persons 65 years & over • 72% perceive influenza immunisation as effective in reducing chance of contracting influenza . • 66% perceive influenza immunisation as effective in reducing severity of influenza . • More than 48% do not consider themselves at risk of contracting influenza.
National Influenza Survey Persons aged 40-64 years.
Persons aged 40 to 64 years. • 35% in groups identified as “at risk” of complications, and/or, HCW working with elderly or immuno-compromised persons. • 32 % of persons in these groups reported immunisation. • 48% of those immunised received free (unfunded) vaccine.
SERCIS Reports website references • National Influenza survey (A population survey of vaccination uptake in Australia) SERCIS, October 2000.
http://www.dhs.sa.gov.au/pehs/CPSE/flu-vaccination2000.pdf
• South Australian Influenza survey. SERCIS, November 2001.
http://www.dhs.sa.gov.au/pehs/CPSE/influenza-survey01.pdf