IDWeek 2023: Seasonal Flu Vaccine Offers More Protection for Immunocompetent Adults than Immunocompromised Peers, but “Difference not Statistically Significant”

This article is part of our IDWeek 2023 coverage. You can find all of our news here.

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The effectiveness of the seasonal influenza vaccine during the 2017-2018 season against symptomatic infection among nonhospitalized patients was lower among immunocompromised (IC) persons than in nonimmunocompromised (non-IC) participants, according to new research.

In a new study of over 5600 nonhospitalized participants with acute respiratory illness with cough, researchers found that vaccine effectiveness (VE) among the non-IC group was 31% compared to -4% among those in the IC arm, “though the difference was not statistically significant,” they wrote in the study abstract.

The findings are being presented during a poster session at IDWeek 2023, being held from October 11-15 in Boston, MA.

“IC individuals have a higher risk of severe influenza and influenza-related hospitalizations, and understanding the VE of the seasonal influenza vaccines in IC populations remains paramount,” wrote presenting author Kailey Hughes Kramer, PhD, MPH, assistant professor, Division of Infectious Diseases, Department of Medicine, University of Pittsburgh School of Medicine, Pennsylvania, and colleagues.

Citing a lack of literature on influenza VE in IC populations, Kramer and coauthors conducted the current study to estimate the VE of the 2017-2018 seasonal influenza vaccine in IC adults compared to non-IC adults using data from the 2017-2018 US Flu VE Network.

Participants with an acute respiratory illness with cough within 7 days of symptom onset were enrolled from outpatient sites in 5 US states, according to the abstract. All participants submitted a respiratory specimen for influenza testing by PCR; those with a positive PCR were cases and those with a negative were controls. IC status was determined by ICD-10 codes.

“We used logistic regression and adjusted for enrollment site, race, self-reported general health status, age, and onset date of symptoms. Separate models were used to calculate and compare the VE for non-IC and IC among outpatient adults >18 years,” stated investigators.

FINDINGS

A total of 5671 participants (64.5% women; mean age, 48 years) were included in the adult analytic dataset, of whom 455 (8%) were IC, according to the results.

Researchers found that VE among participants in the non-IC group was 31% (95% CI, 22 to 39) and among IC participants was -4% (95% CI, -66 to 35) after adjusting for enrollment site, race, self-reported general health status, age, and tertile of illness onset date. P-value for interaction by IC status was 0.100, noted investigators.

“Although statistical significance was not met, this study demonstrated the capacity to use an existing flu VE network to study a large IC population and can be used as the framework for large multicenter VE studies for IC populations,” concluded Kramer et al.

Source: Effectiveness of the influenza vaccine for preventing laboratory-confirmed influenza infections in outpatient immunocompromised adults, 2017-2018. Abstract presented at IDWeek; October 11-15, 2023; Boston, MA.

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