Effectiveness of Influenza Vaccine for Preventing Laboratory-Confirmed Influenza Hospitalizations in Immunocompromised Adults

Background: Yearly influenza immunization is recommended for immunocompromised (IC) individuals, although immune responses are lower than that for the nonimmunocompromised and the data on vaccine effectiveness (VE) in the IC is scarce. We evaluated VE against influenza-associated hospitalization among IC adults.

Methods: We analyzed data from adults ≥ 18 years hospitalized with acute respiratory illness (ARI) during the 2017-2018 influenza season at 10 hospitals in the United States. IC adults were identified using prespecified case definitions using electronic medical record data. VE was evaluated with a test-negative case-control design using multivariable logistic regression with polymerase chain reaction-confirmed influenza as the outcome and vaccination status as the exposure, adjusting for age, enrolling site, illness onset date, race, days from onset to specimen collection, self-reported health, and self-reported hospitalizations.

Results: Of 3524 adults hospitalized with ARI, 1210 (34.3%) had an immunocompromising condition. IC adults were more likely to be vaccinated than non-IC (69.5% vs 65.2%) and less likely to have influenza (22% vs 27.8%). The mean age did not differ among IC and non-IC (61.4 vs 60.8 years of age). The overall VE against influenza hospitalization, including immunocompetent adults, was 33% (95% confidence interval [CI], 21-44). VE among IC vs non-IC adults was lower at 5% (95% CI, -29% to 31%) vs 41% (95% CI, 27-52) (P < .05 for interaction term).

Conclusions: VE in 1 influenza season was very low among IC individuals. Future efforts should include evaluation of VE among the different immunocompromising conditions and whether enhanced vaccines improve the suboptimal effectiveness among the immunocompromised.