Results of a study published in Journal of Infection found that influenza vaccination reduced influenza-like illness diagnoses and the distribution of antibiotic prescriptions among younger to middle-aged adults.
Researchers at universities in Australia and New Zealand sourced data for this case-control study from MedicineInsight, an Australian national health care database. Influenza vaccine effectiveness (VE) was estimated among adults (age, ≥40 years) who were and were not (controls) diagnosed with influenza-like illness between June and September of each year from 2015 through 2018. The researchers used generalized estimating equations to estimate influenza VE overall, with adjustments for age (<65 vs 65≥ years) and comorbidities. They also evaluated antibiotic prescription practices among various subsets of patients diagnosed with influenza-like illness.
The number of patients diagnosed with influenza-like illness varied from a low of 558 patients in 2018 to a high of 2901 in 2017, and the number of diagnosed control patients ranged from 86,618 in 2015 to 136,763 in 2017. In general, diagnosed patients were younger, had a history of asthma, received antibiotic therapy in the previous year, lived in a major city, and had not been vaccinated in the previous or current season compared with those in the control group.
Stratified by week and year, 2017 was the most contagious year at its peak (adjusted odds ratio [aOR], 9.72; 95% CI, 6.89-13.73; P <.001) compared with other years, such as 2018 (aOR, 1.62; 95% CI, 1.04-2.51; P =.03).
The percentage of patients who received an antibiotic prescription on the same day as their influenza-like illness diagnosis was 21% across all 4 seasons. For vaccinated and unvaccinated patients, this percentage ranged from 20% to 29% and 17% to 24%, respectively.
In the pooled analysis, influenza vaccination was associated with an estimated VE of 24% for protection against influenza-like illness (aOR, 0.76; 95% CI, 0.66-0.89; I2 =74%). Further analysis showed vaccinated patients with influenza-like illness were less likely to receive an antibiotic prescription, but the overall effect of vaccination on reducing antibiotic prescriptions was not significant (aOR, 0.85; 95% CI, 0.71-1.03).
In subgroup analyses, influenza vaccination was associated with significant protection against influenza-like illness among patients younger than 65 years (VE, 27%; aOR, 0.73; 95% CI, 0.62-0.87) and those without comorbidities (VE, 24%; aOR, 0.76; 95% CI, 0.66-0.88). Vaccination also conferred significant protection among patients who were (VE, 27%; aOR, 0.73; 95% CI, 0.57-0.93; ) and were not (VE, 22%; aOR, 0.78; 95% CI, 0.69-0.87) vaccinated in the previous season, as well as those who had 4 or more health care encounters within the past year (VE, 21%; aOR, 0.79; 95% CI, 0.71-0.88).
Subgroup analyses also showed influenza vaccination significantly reduced antibiotic prescription outcomes among patients younger than 65 years (VE, 23%; aOR, 0.77; 95% CI, 0.62-0.97) and those without comorbidities (VE, 22%; aOR, 0.78; 95% CI, 0.61-0.99).
Limitations of this study include potential misclassification bias in regard to both influenza-like illness diagnoses and antibiotic prescription outcomes, and the inability to determine the effect of influenza testing on antibiotic prescribing practices.
“Our findings of reduced antibiotic prescription would support cost-effectiveness analysis of influenza vaccine programs for a wider adult cohort,” the researchers concluded.
He W-Q, Gianacas C, Muscatello DJ, et al. Effectiveness of influenza vaccination in reducing influenza-like illness and related antibiotic prescriptions in adults from a primary care-based case-control study. J Infect. Published online October 23, 2022. doi:10.1016/j.jinf.2022.10.028