Association of influenza vaccination and long-term outcomes among patients with cardiopulmonary disease: A nationwide population-based cohort study.

BACKGROUND

Influenza infection remains a major cause of illness and death among the elderly and high-risk groups. Besides respiratory illnesses (RTIs), influenza is increasingly recognized as a trigger for cardiovascular diseases (CVDs). The long-term and cumulative effects of vaccination remain unclarified.

METHODS

We conducted a population-based cohort study using the Longitudinal Health Insurance Database, a random subset of the Taiwan National Health Insurance Research Database to evaluate the associations among influenza vaccination and subsequent CVDs, RTIs, renal disease, and sepsis. Diagnoses and outcomes were ascertained using ICD-9-CM codes.

RESULTS

Throughout a two-year period, individuals who received the influenza vaccine had a lower risk of CVDs [adjusted hazard ratio (aHR) = 0.617, p < 0.001], RTIs (aHR = 0.559, p < 0.001), and antiviral drug use (aHR = 0.707, p = 0.010) compared to the unvaccinated group. During the entire follow-up period (2000-2015), vaccinated individuals continued to have a reduced risk of developing CVDs (aHR = 0.723, p = 0.002) and RTIs (aHR = 0.614, p < 0.001) relative to their unvaccinated counterparts. Those who received three doses exhibited lower risks of CVDs (aHR = 0.638, p < 0.001), RTIs (aHR = 0.580, p < 0.001), and antiviral drug use (aHR = 0.718, p = 0.010) compared to unvaccinated individuals.

CONCLUSIONS

We demonstrated that influenza vaccination was associated with a significantly lower risk of developing CVDs and RTIs during both 2-year and 16-year follow-up periods. Repeated influenza vaccination confers cumulative protection against CVDs and RTIs. Vaccinations also reduced the use of antiviral drugs over two years after vaccination and with repeated doses.