As previously discussed, people with diabetes are especially vulnerable to all infectious diseases, including influenza. Recently, people with diabetes were reported to have the second-highest mortality risk from COVID-19. Before highlighting the need for vaccination, however, it is necessary to evaluate the factors associated with the influenza VCR among people with diabetes. Previous South Korean studies that investigated the influenza VCR and associated factors have focused either on the general population [26, 27] or those with other chronic diseases [19, 20].
As people with diabetes are more susceptible to influenza and have a greater risk of medical complications from infection, the WHO and several National Immunization Technical Advisory Groups recommend annual influenza vaccination [28, 29].
A systematic review and meta-analysis of people with diabetes demonstrated that the effectiveness of the influenza vaccine differs slightly according to age . Overall, the effectiveness of the influenza vaccine among working-age people (18–64 years) was 58%. Although hospitalization due to influenza or pneumonia did not affect the overall mortality rate, it was found that vaccination for influenza decreased the hospitalization rate among people with diabetes of working age. In addition, vaccination for influenza among older adults (over 65 years old) has been demonstrated to reduce mortality rates from all causes, hospitalization rates from all causes, and hospitalization rates from influenza or pneumonia .
The findings mentioned above prove that the influenza vaccine is important, regardless of age and comorbid diseases. Thus, efforts to increase the influenza VCR are required. VCRs vary from country to country, and the factors affecting the rate within each country are different . Therefore, in this analysis, we sought to identify the factors associated with the influenza VCR in South Korea.
According to the most recent data, the influenza VCR among people with diabetes in South Korea was 60.6%. In a recent analysis, the goal was to increase the influenza VCR to 90% among people over 65, and 60% among high-risk groups aged 18–64 in the USA . In comparison with these numbers, the VCR in South Korea has met the target rate. The high VCR can be attributed to the South Korean medical system. In South Korea, the National Health Insurance Service is mandatory for everyone. Under this program, people receive deductions for a significant portion of medical costs. They also receive benefits when utilizing health management services. The cost of influenza vaccination varies slightly depending on the type of vaccine and hospital but does not exceed $50. As per the national policy, people aged above 65 receive free immunization.
Although the VCR across risk groups and countries continues to increase, few countries are close to achieving the VCR target set by the WHO . In the univariate analysis, many variables, such as gender, educational level, smoking, exercise, drinking, marital status, private health insurance, activity limit, economic activity, age, and EQ-5D score, were found to be associated with the VCR. However, the multivariate analysis revealed that only age and economic activity were associated with the VCR. Our findings demonstrated that there are only two individual patient factors (not employed and old age) that are associated with VCRs. In a previous Korean study of 32,268 individuals who participated in the KNHANES III–VI (2005–2015), the influenza VCR among diabetic patients was 50.0%, which was lower than our results. For the non-diabetes group, the VCR was 38.2%, which was higher than our results. Influenza VCR in diabetic patients was associated with socioeconomic (old age, female sex, high family income, medical assistance insurance) and health-related factors (dangerous drinking, obesity, lack of recent health screening) .
A study of 10 countries in Africa, Asia–Pacific, Eastern Europe, Latin America, and the Middle East demonstrated that the influenza VCR is not affected by patient factors . This is similar to our findings and suggests that national programs are necessary to increase the influenza VCR . Indeed, the UK has achieved its target VCR, and this is the result of active national support and health programs .
Although the rates were calculated in different years, a study conducted in five European countries demonstrated that the influenza VCRs among patients with chronic diseases, such as diabetes, were as follows: 59.4% in the UK, 29.8% in Germany, 36.7% in Italy, 34.4% in France, and 37.1% in Spain .
In a large-scale study in European countries conducted after the previously mentioned study, an increase in VCRs was observed . However, they still did not reach the rate recommended by the WHO, indicating that management at the national level is necessary .
Contradictory to our results, some studies have suggested that several factors affect VCRs. A study in Singapore revealed that high income and high educational levels were associated with high VCR . A study in Spain demonstrated that the following factors affect the influenza VCR: age, urban residence, income, marriage, health awareness, and caregivers . A study of older adults in Brazil revealed that the factors that increase the influenza VCR include old age, being male, high income, high educational level, non-smoking, and solicitation . In Canada, research demonstrated that higher education, higher income, smoking, increased levels of drinking, poor health perception, exercise, and city dwelling increased the influenza VCR . A nationwide study in Spain revealed that old age, previous vaccination, chronic disease, and being female increased the influenza VCR among the vulnerable population . In France, it was demonstrated that VCRs were higher in families with infants, higher educational levels, professional occupations, and previous influenza vaccination .
Influenza, which can be prevented through vaccination, causes significant economic losses. In the USA, the total annual cost related to influenza is €10,000–17,000 million . French research estimates that the total cost related to influenza is over €1796 million per year . These economic losses highlight the importance of increasing the influenza VCR.
Based on the most recent data, we analyzed the factors associated with the influenza VCR among people with diabetes in South Korea. However, it does have limitations. First, owing to the use of cross-sectional data, causality cannot be established. Second, not all factors that could be associated with vaccination history were considered. According to Korea’s national policy, people over the age of 65 years are eligible for free vaccinations. Therefore, it is possible that the results of this analysis are biased. However, the reason why we included individuals aged 65 years and older and examined their employment status was to analyze the factors that affect the overall VCR in Korea, including the special policy background of Korea.