In older adults with breakthrough influenza, high-dose (HD) vaccination was associated with a reduction of approximately 20% in post-influenza mortality, according to study findings published in Clinical Infectious Diseases.
Researchers sought to determine whether HD vaccination affected disease severity in adults aged 65 and older with breakthrough influenza, using US claims data for 3 influenza seasons (2016-2017; 2017-2018; and 2018-2019).
The retrospective cohort study included 44,456 individuals age 65 and older who had either visited the emergency department (ED) or been admitted to a hospital (index event) with a diagnosis of influenza. Of those, 2301 (52%) were non-vaccinated (NV), 15,037 (33.8%) had received the HD vaccination, and 6310 had received the standard dose (SD) vaccination. Patients were considered vaccinated if they had received the vaccine at least 14 days prior to hospital admission/ED visit for influenza. The primary outcome was mortality within 30 days of an influenza diagnosis received during an ED visit or hospitalization.
The investigators conducted 3 sets of comparisons of the HD, SD, and NV cohorts: high-dose (HD) vs non-vaccinated (NV), HD vs standard-dose (SD), and SD vs NV. This was done to mitigate potential confounding factors and biases related to health care, vaccine access, and specific vaccine types when comparing the patient cohorts.
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HD vaccination was associated with lower post-influenza mortality among older adults with breakthrough influenza, even during seasons where antigenically drifted H3N2 circulated.
The analysis of mortality rates found that in the 2016 to 2017 season, there was a 29% decrease in mortality between HD and NV cohorts, followed by a reduction of 17% and 27% in 2017 to 2018 and 2018 to 2019 seasons, respectively. During the 2016 to 2017 season, researchers noted a similar reduction in mortality associated with SD vaccination compared to NV (incidence rate ratio, 0.75; CI, 0.57-0.98). There was no observable decrease in mortality between recipients of HD and SD vaccines during the 2016 to 2017 season, as both vaccines provided similar levels of protection. However, the HD group showed a 17% to 20% reduction in mortality compared with the SD group in subsequent seasons, although the difference was not statistically significant.
Study limitations include the observational design; the absence of laboratory confirmation for influenza; the potential misclassification of unvaccinated patients due to the use of claims data; and the possibility of residual confounding.
The study authors concluded that “HD vaccination was associated with lower post-influenza mortality among older adults with breakthrough influenza, even during seasons where antigenically drifted H3N2 circulated.”
Disclosures: This research was supported by Sanofi Vaccines. Some of the study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of disclosures.
