From the Journals

Influenza vaccination modestly reduces risk of hospitalizations in patients with COPD



Influenza vaccination modestly reduces the risk of hospitalizations associated with laboratory-confirmed influenza in people with chronic obstructive pulmonary disease (COPD), according to data published in the Journal of Infectious Diseases.

This negative-stained transmission electron micrograph depicts the ultrastructural details of an influenza virus particle, or a virion. Cynthia Goldsmith/CDC photo #10073

“To the best of our knowledge, this is the first large, real-world population study to examine vaccine effectiveness in people with COPD using the test-negative design and influenza-specific study outcomes,” wrote Andrea S. Gershon, MD, of Sunnybrook Health Sciences Center in Toronto and colleagues. “These findings emphasize the need for more effective influenza vaccines for older COPD patients and other preventive strategies.”

A test-negative study design

Data suggest that 70% of COPD exacerbations are caused by infection, and influenza often is identified as the cause. Although all major COPD practice guidelines recommend seasonal influenza vaccination, the evidence indicating that vaccination reduces hospitalizations and death is limited. The inherent or corticosteroid-induced decrease in immune response to vaccination and respiratory infection among patients with COPD may reduce the effectiveness of influenza vaccination, wrote Dr. Gershon and colleagues.

The investigators used a test-negative design to evaluate how effectively influenza vaccination prevents laboratory-confirmed influenza–associated hospitalizations in community-dwelling older patients with COPD. They chose this design because it attenuates biases resulting from misclassification of infection and from differences in health care–seeking behavior between vaccinated and unvaccinated patients.

Dr. Gershon and colleagues examined health care administrative data and respiratory specimens collected from patients who had been tested for influenza during the 2010-2011 to 2015-2016 influenza seasons. Eligible patients were aged 66 years or older, had physician-diagnosed COPD, and had been tested for influenza within 3 days before and during an acute care hospitalization. The researchers determined influenza vaccination status using physician and pharmacist billing claims. They obtained demographic information through linkage with the provincial health insurance database. Multivariable logistic regression allowed Dr. Gershon and colleagues to estimate the adjusted odds ratio of influenza vaccination in people with laboratory-confirmed influenza, compared with those without.

Effectiveness did not vary by demographic factors

The investigators included 21,748 patients in their analysis. Of this population, 3,636 (16.7%) patients tested positive for influenza. Vaccinated patients were less likely than unvaccinated patients to test positive for influenza (15.3% vs. 18.6%). Vaccinated patients also were more likely to be older; live in an urban area; live in a higher income neighborhood; have had more outpatient visits with a physician in the previous year; have received a prescription for a COPD medication in the previous 6 months; have diabetes, asthma, or immunocompromising conditions; have a longer duration of COPD; and have had an outpatient COPD exacerbation in the previous year.

The overall unadjusted estimate of vaccine effectiveness against laboratory-confirmed influenza–associated hospitalizations was 21%. Multivariable adjustment yielded an effectiveness of 22%. When Dr. Gershon and colleagues corrected for misclassification of vaccination status among people with COPD, the effectiveness was estimated to be 43%. Vaccine effectiveness did not vary significantly according to influenza season, nor did it vary significantly by patient-specific factors such as age, sex, influenza subtype, codiagnosis of asthma, duration of COPD, previous outpatient COPD exacerbations, previous COPD hospitalization, previous receipt of inhaled corticosteroids, and previous pneumonia.

One limitation of the study was the possibility that COPD was misclassified because not all participants underwent pulmonary function testing. In addition, the estimates of vaccine effectiveness in the present study are specific to the outcome of influenza hospitalization and may not be generalizable to vaccine effectiveness estimates of outpatient outcomes, said the investigators. Finally, Dr. Gershon and colleagues could not identify the type of vaccine received.

“Given that a large pragmatic randomized controlled trial evaluating influenza vaccination would be unethical, this is likely the most robust estimate of vaccine effectiveness for hospitalizations in the COPD population to guide influenza vaccine recommendations for patients with COPD,” wrote Dr. Gershon and colleagues.

An Ontario Ministry of Health and Long-Term Care Health Systems Research Fund Capacity Grant and a Canadian Institutes of Health Research operating grant funded this research. One investigator received grants from the Canadian Institutes of Health Research during the study, and others received grants from pharmaceutical companies that were unrelated to this study.

SOURCE: Gershon AS et al. J Infect Dis. 2019 Sep 24. doi: 10.1093/infdis/jiz419.

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