The European Journal of Public Health Advance Access originally published online on October 27, 2006
The European Journal of Public Health 2007 17(3):272-277; doi:10.1093/eurpub/ckl242
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Infectious and allergic diseases, cancer, and diabetes |
Influenza vaccination among the elderly Spanish population: trend from 1993 to 2003 and vaccination-related factors*
Ana Lopez de Andres1, Pilar Carrasco Garrido2, Valentín Hernández-Barrera2, Silvia Vázquez-Fernández del Pozo2, Ángel Gil de Miguel2 and Rodrigo Jiménez-García2
1 Preventive Medicine Unit, Alfonso X el Sabio University, Villanueva de la Cañada Campus Madrid, Spain
2 Preventive Medicine and Public Health Teaching and Research Unit, Health Sciences Faculty, Universidad Rey Juan Carlos, Avda de Atenas s/n, Alcorcón 28922 Spain
* This study forms part of a research project funded by a FIS (Fondo de Investigaciones Sanitarias-Health Research Fund) grant PI041662 from the Carlos III Institute of Public Health. Madrid Spain
Correspondence: Rodrigo Jiménez García, Unidad de Docencia e Investigación en Medicina Preventiva y Salud Pública, Facultad de Ciencias de la Salud, Avda. de Atenas, s/n. 28922 Alcorcón, Spain, tel.: +34 91 4888853, fax: +34 91 4888848, e-mail: rodrigo.jimenez{at}urjc.es
Received June 27, 2006, accepted September 14, 2006
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Abstract |
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Background: Influenza is an important public health problem that particularly affects elderly subjects and influenza vaccination is a safe, effective and efficient method for prevention of influenza-related complications in elderly individuals with or without underlying chronic conditions. This study aims to analyze adjusted time trends in the coverage of influenza vaccination among elderly Spanish subjects and to identify which variables were associated with the probability of having been vaccinated in 2003. Methods: We undertook a cross-sectional study using data of individuals aged
65 years drawn from the 1993, 1995, 1997, 2001, and 2003 Spanish National Health Surveys. The answer to the question 'Did you have a ’flu shot in the latest campaign‘ was used as the dependent variable, and socio-demographic and health-related characteristics were analyzed as independent variables. Coverage of vaccination for each year was adjusted by the direct method for both age and gender. Multivariate logistic regression was used to estimate the independent effect of variables on the receipt of influenza vaccine. Results: 15 989 records were analyzed. Adjusted influenza coverage increased from 50.1% in 1993 to 63.7% in 2003 (P < 0.001). The variables that were significantly associated with a higher likelihood of being vaccinated were older age, suffering a chronic disease, residence in towns with <10 000 inhabitants, ‘worse’ self-perceived health and non-smokers. Conclusions: Coverage among the Spanish elderly has increased significantly from 1993 to 2003. Still, there is room for improvement, particularly, among the subjects with ‘good’ self-perceived health, those with no concomitant medical conditions, and smokers.
Keywords: epidemiology, influenza, survey, vaccine
Influenza is an important public health problem that particularly affects elderly subjects and subjects of any age with underlying medical disorders. Different studies indicate that among individuals aged 65 years, influenza is associated with elevated morbidity and mortality, and excess hospitalizations.1–3 Clinical trials and observational studies have shown that annual influenza vaccination is a safe, effective, and efficient method for prevention of influenza-related complications in elderly individuals with or without underlying chronic diseases.4–7
As in other countries across Europe and America, influenza vaccination has been universally indicated for more than 15 years in Spain for adults over the age of 64 years and is administered free of charge.8–10
Spain ranks as having one of the highest distributions of influenza vaccines per inhabitant in the world (212/1000 population in 2003), with influenza vaccination rates among the elderly being close on 60%.9,11 In the United States, the highest coverage levels (68%), in this group of individuals, were attained during the 1999–2000 season, with this figure declining to 65.6% in 2003.10 In Europe, major inter-country variations are in evidence, coverage ranging from of >70% in The Netherlands to only 18% in Poland.12–14
These results point to the existence of limitations on reaching the maximum vaccination potential among the elderly population in Spain.9,15
To our knowledge, the only previous study on trends in the coverage of influenza vaccination, which included the Spanish elderly population, was based on data up to 2001 and reported a significant improvement.9 Insofar as predictors of vaccination in the elderly are concerned, data collected in 1997 indicate that factors identified as barriers to receiving the vaccine included younger age, female gender, less contact with the health care system, smoking, and not having high-risk chronic conditions.15
The aims of this study were:
- to analyze age- and gender-adjusted time trends in the coverage of influenza vaccination among elderly Spanish subjects (age 65 years), using data drawn from the Spanish National Health Surveys (NHS) (Encuestas Nacionales de Salud) conducted from 1993 to 2003; and,
- to analyze which socio-demographic and health-status-related variables that were associated with the probability of senior citizens having been vaccinated in 2003.
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Methods |
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We undertook a cross-sectional study on influenza vaccination coverage in Spain, using data drawn from the 1993, 1995, 1997, 2001, and 2003 NHS. These National Health Surveys were conducted on a representative sample of the non-institutionalized Spanish adult population (aged >15 years) using multistage sampling stratified by clusters, with proportional random selection of primary sampling units (towns) and secondary units (sections), and selection of end units (individuals) by random routes with gender and age quotas. Details of NHS methodology are described elsewhere,16–20
The 1993, 1995, 1997, 2001 and 2003 surveys included 21120, 6400, 6400, 21120 and 21650 adults, respectively. Individuals aged 65 years were selected for study purposes from all the above NHS. The answer (‘yes’ or ‘no’) to the question ‘Did you have a ‘flu shot in the latest campaign’ was used as the dependent variable, and the following were analyzed as independent variables: socio-demographic variables, such as age, gender, marital status, income, size of town or city and educational level; and lifestyle- and health-related variables, such as perception of health status, smoking habit, physical exercise, obesity and presence of other associated chronic diseases that constitute a recommendation for influenza vaccination (e.g. diabetes and/or heart disease and/or respiratory diseases). Furthermore, vaccinated subjects were asked whether said vaccination had been administered on medical indication or at their own request. The variables used were created on the basis of identically worded questions in all the surveys used.
Statistical analysis
Influenza vaccination coverage in the five surveys was calculated by defining it as the percentage of individuals aged 65 years that reported having been vaccinated against influenza in the most recent campaign.
Coverage of vaccination in the 1993, 1995, 1997, and 2001 NHS were adjusted by the direct method for both age and gender, with the 2003 Spanish population being taken as the reference population for this purpose.21
A bivariate analysis was performed using the 2003 NHS data, cross-tabulating the independent variables with the variable of influenza vaccination. The statistical Chi-squared method was used for bivariate comparison of proportions; with statistical significance being set at P < 0.05 (P-values are two-tailed).
To estimate the independent effect of variables on the receipt of influenza vaccine, adjusted odds ratios (ORs) were obtained by using multivariate logistic regression models. All estimates was made by incorporating the complex sampling design and weighting factors, using the ‘svy’ (survey commands) functions of the STATA 9.1 program, which enabled us to incorporate the sampling design into our statistical calculations [proportions, confidence intervals (CIs), Chi-squared, logistic regression].
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Results |
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A total of 3342, 1152, 1141, 4220, and 6134 records on individuals aged
65 years were analyzed in the 1993, 1995, 1997, 2001, and 2003 NHS, respectively. Table 1 shows influenza coverage by age and gender group, observed and adjusted for the years studied. Across the study period, adjusted influenza coverage among elderly individuals went from 50.1% in 1993 to 63.7% in 2003, with this variation proving statistically significant (P < 0.001). This trend was statistically significant for men and women alike (P < 0.001). It may be seen from Table 2 that the reason most cited for having an influenza vaccination was medical prescription in the five NHS analyzed, with this rising from 80.5% in 1993 to 87.6% in 2003 (P < 0.001).
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Among the senior citizens included in the 2003 NHS it is seen that, as in previous National Health Surveys, the coverage, both among men and women, increased significantly with age (P < 0.001). In 2003, there were no significant differences between the genders. Table 3 shows coverage of vaccination according to the socio-demographic and health-status-related variables studied for the elderly subjects included in the 2003 NHS.
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In the bivariate analysis, the extent of coverage was observed to be significantly higher among subjects resident in towns of up to 10 000 inhabitants, persons with worse self-perceived health, those who suffered from an associated chronic disease, and non-smokers. In all, 40.4% of the subjects analyzed presented with at least one associated chronic disease.
The results of the multivariate analysis are shown in Table 4. The variables that were significantly associated with a higher likelihood of being vaccinated were the same as those which proved significant in the bivariate analysis. The probability of being vaccinated was 2.37 times higher if the subject's age was 75 years versus 65–69 years, and 1.58 times higher if the subject suffered from a concomitant chronic disorder or disease.
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Discussion |
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The adjusted results of the surveys used reveal that influenza vaccination coverage among the Spanish elderly population has improved steadily and significantly from 1993 to 2003. In our study, an overall coverage of 63.7% was obtained for this population in 2003. In a survey conducted on the general population in four European countries in 2004, a coverage of 67% was obtained for Spanish subjects aged
65 years, with comparable figures being 53% for Germany, 46% for Sweden, and 18% for Poland.14 In The Netherlands, data from three different sources estimated that in the 2001–2002 season, vaccination coverage among the elderly ranged from 74 to 81%.13 In the United States, a study undertaken using a methodology similar to ours, reported a vaccination coverage among the elderly of 65.6% in 2002, as well as a favorable trend in coverage from 1989 to 2002, findings in line with those of our study 22
In our opinion, possible explanations for the increase in coverage in the Spanish elderly population are, among others, the improvement in access to health services, the greater intensity and effectiveness of vaccination promotion campaigns in recent years, and a higher participation by health professionals. In support of this last point, we found that in our study, the percentage of subjects who reported to being vaccinated due to medical indication increased significantly across the study period. The importance of the medical practitioner in ensuring that subjects for whom influenza vaccination is indicated are indeed vaccinated has been highlighted in a number of studies, including some that were undertaken in Spain.23–26 Analysis of the factors associated with influenza vaccination in the Spanish elderly population showed that the older the age, the greater the likelihood of being vaccinated. The influence of age on influenza vaccination appears almost constantly in studies on vaccination predictors, both for subjects aged over and under 65 years, as well as among those with or without associated chronic diseases.9,12,15,22,25,27–29
In our study, suffering from an associated chronic disease increased the probability, 1.58-fold, of a senior citizen reporting to having been vaccinated in 2003. Like age, the influence of co-morbidity as a predictor of vaccination in the elderly has already been reported previously.9,15,22 Indeed, Lu et al.22 obtained an adjusted OR of 1.5 for US senior citizens versus those without a medical condition.
A noteworthy finding yielded by our study was the fact that in the smallest towns, the elderly registered a higher coverage of vaccination. In our opinion, the explanation for this may lie in the fact that the proximity of and accessibility to health centers is greater in such places.28 In a study linked to the use of preventive medical services in the USA, for influenza, a coverage of 55% was obtained for urban elderly subjects and 58% for those who resided in rural areas.30
Smoking as a negative predictor of influenza vaccination is in line with the results of Sarria-Santamera and Timoner15 in their analysis of the Spanish elderly population included in the 1997 NHS, and with the results of two studies undertaken in Spain with subjects affected by diabetes and COPD.27,28 Moreover, similar results have been reported by other authors.25,31
After multivariate adjustment, we observed that elderly subjects with worse self-perceived health registered higher vaccination rates. This association between greater use of influenza vaccine by subjects who have a more negative perception of their health status has also been found in different studies conducted on the general population, across all age groups, and in other studies targeting high-risk populations.25,29,32,33
Some strategies that have demonstrated their effectiveness for the purpose of enhancing the coverage of vaccination among the elderly, and must be considered, include: lowering the age at which the influenza vaccine recommendation becomes universal; telephoning or mailing personal reminders; compliance monitoring; using computerized systems to identify high-risk patients; improving medical records; empowering nurses to vaccinate patients directly; and drawing up purpose-made influenza-vaccination time tables.34–36
There are a number of possible limitations to this study. First, the use of non-validated self-reported data on vaccination could entail possible bias. In this respect, however, several studies among elderly subjects which have compared the results of self-response against medical records, observe that self-response on influenza vaccination is highly sensitive and evinces a high degree of agreement.37–39 Second, another possible limitation of the NHS is that the validity of the questions used to classify subjects as having ‘high-risk medical conditions’ has not yet been evaluated. Moreover, some conditions associated with increased risk of influenza complications are not included in the NHS.
Third, as the NHS only include non-institutionalized subjects, our results cannot be generalized to the institutionalized Spanish population.
Fourth, the initial response rate to the 2003 NHS was 67%, so that the existence of a possible non-response bias must therefore be considered.40
Finally, it should be pointed out that the 1995 and 1997 NHS included far fewer subjects than the 1993, 2001, and 2003 surveys. This was due to the fact that the NHS for these 2 years had no Autonomous Regional representativeness.17,18 The influence of this difference in the sampling technique on point estimates must be borne in mind.
As strengths of the study, it should be stressed that the Spanish National Health Surveys have previously been used by Spanish researchers to study different health-related issues, including anti-influenza vaccination, and that the questions used by us remained identical across all the surveys used for study purposes.9,15,27,41,42
A number of authors have shown that surveys conducted on the general population are a useful tool for studying influenza vaccination coverage.12–14,43,44 The National Health Interview Survey (NHIS) conducted periodically in the United States, with a methodology and content similar to the Spanish NHS, is used systematically for the study of vaccination coverage, its evolution, and associated factors.10,22,29,43,44
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It can therefore be said that, although coverage of influenza vaccination among Spanish elderly has increased steadily and significantly from 1993 to 2003, there is still room for improvement, particularly among subjects with good self-perceived health, those with no concomitant medical conditions, and smokers.
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Acknowledgments |
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This study forms part of a research project funded by a FIS (Fondo de Investigaciones Sanitarias-Health Research Fund) grant PI041662 from the Carlos III Institute of Public Health.
Conflict of Interest: ‘none declared’.
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