Major Finding: The odds ratio of having acute asthma episodes for the vaccinated group was 0.78, when the instrumental variables method was used.
Data Source: A retrospective cohort of 138,935 children and adults with persistent asthma drawn from the MarketScan Commercial Claims and Encounters database, 22% of whom received the seasonal flu vaccine.
Disclosures: Dr. Saha said the findings do not represent the official position of the CDC. He reported no conflicts of interest.
ATLANTA — Individuals with persistent asthma who received the seasonal influenza vaccination appeared to have fewer episodes of acute asthma than did those who were not vaccinated, according to Shubhayu Saha, Ph.D., of the Centers for Disease Control and Prevention's National Center for Environmental Health.
The findings corroborate current guidelines that recommend the vaccine for patients with persistent asthma, Dr. Saha said in a poster presentation at the conference sponsored by the CDC.
A retrospective cohort of children and adults who met the HEDIS (Healthcare Effectiveness Data and Information Set) definition of persistent asthma was drawn from the MarketScan Commercial Claims and Encounters database, Dr. Saha commented.
Those with chronic obstructive pulmonary disease, cystic fibrosis, and emphysema were excluded from the study.
Of 138,935 individuals in the cohort, 22% received the vaccine in the 2006-2007 flu season (August 2006 to March 2007).
Bivariate comparisons indicated that acute asthma episodes requiring an emergency department visit and/or hospitalization during the follow-up period were more frequent in those who received the vaccine (4.9%) than in those who did not (4.0%), Dr Saha and his investigators reported.
However, those in the treatment group also were younger, had higher Charlson comorbidity scores, used more controller medications, and had more acute asthma episodes in the past.
To control for potential confounding where asthma patients with poorer prognoses also were more likely to get the influenza vaccine, the investigators used instrumental variable and propensity score matching methods to obtain unbiased estimates of the effect of vaccine on acute asthma episodes, Dr. Saha explained.
Each approach yielded similar and statistically significant results'results that were contrary to those of the bivariate comparisons.
Controlling for age, sex, region, health plan, comorbidity, and past asthma exacerbation, the instrumental variables method indicated the odds ratio of having acute asthma episodes for the vaccinated group was 0.78.
When the propensity score matching methods were used with four different matching algorithms, the vaccinated group consistently had an odds ratio of 0.7 for experiencing acute asthma episodes, the investigators reported.
“Estimates from both instrumental variable regression and propensity score matching show [the] significant protective effect of the influenza vaccination in reducing acute asthma episodes among individuals with persistent asthma in a population with employer-based health insurance,” Dr. Saha said.
The researchers involved in this study acknowledged several limitations.
The data did not include factors such as ethnicity and income.
Moreover, the claims data did not capture vaccines received outside of the health plan—for instance, at a retail clinic or school.
Because the research was limited to an employer-based population, the findings cannot be readily generalized to other populations, Dr. Saha and his associates said.