A new study of over 56,000 COPD patients found that the influenza vaccine may reduce the risk of flu-related hospitalizations by 39 percent, though researchers caution that additional studies are needed to confirm these findings and address potential confounding factors.
- The flu vaccine reduced hospitalized influenza risk in COPD patients with a hazard ratio of 0.61 during epidemic periods
- Study included 56,652 matched pairs of vaccinated and unvaccinated COPD patients aged 40 and older
- Researchers used a novel study design to address immortal time bias and residual confounding issues from previous vaccine research
- Secondary outcomes showed reduced risk of acute COPD exacerbations and pneumonia during flu seasons, with a 0.89 hazard ratio
- Researchers emphasize more methodological improvements are needed to better understand residual confounding in influenza vaccine effectiveness studies
The common flu vaccine may help reduce the risk of influenza-related hospitalizations in COPD patients, but there is a caveat and more research is needed.
The paper, “Influenza Vaccine Effectiveness in Patients With Chronic Obstructive Pulmonary Disease: A Cohort Study Emulating a Randomized Trial,” was published in Clinical Microbiology and Infection.
Researchers used a novel study design to address previous observational studies of the influenza vaccine that faced issues of residual confounding (wherein errors or variations in study results remain even after control for confounding factors) and immortal time bias (a period of time during follow-up when people in the exposed group cannot experience the outcome).
The cohort study was conducted emulating a randomized trial within primary care practices that contribute data to England’s Clinical Practice Research Datalink. The researchers identified the base cohort of patients diagnosed with COPD, aged 40 and older, using inhaled treatment.
COPD patients vaccinated between September 2014 and March 2020 were matched 1:1 with unvaccinated COPD patients. The hazard ratio (HR) for hospitalized influenza was 0.61 during epidemic periods. Secondary outcomes included a composite of acute exacerbations of COPD, pneumonia and hospitalized influenza, with a 0.89 HR during epidemic periods and 0.99 HR outside influenza seasons. Urinary tract infections during those same periods were used to detect any residual confounding.
The researchers included 56,652 matched pairs of vaccinated and unvaccinated patients with COPD. Influenza vaccine was associated with a reduced risk of hospitalized influenza in patients with COPD, but the researchers cautioned that a reduced risk of urinary tract infection suggests an important residual confounding and more research is needed.
“While this study design addresses immortal time bias, methodological improvements are needed to better address residual confounding in cohort studies of the influenza vaccine,” researchers wrote. “In the meantime, negative control outcomes should be assessed during influenza epidemics to better detect residual confounding.”
