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Evaluation

Oral Presentation

Session: Vaccine Safety Across Ages & Platforms

Assessment of Potential Adverse Events Following the 2022–2023 Seasonal Influenza Vaccines Among U.S. Adults Aged 65 Years and Older

Monday, August 26, 2024
2:30 PM – 2:45 PM CEST
Location: Conv Hall I C
Background: Each year millions of people receive influenza vaccines formulated with influenza strains expected to circulate in the upcoming season. Accordingly, monitoring of rare adverse events is important to ensure safety, particularly among persons 65 years and older who may be more vulnerable to adverse events because of comorbidities and declining immune function.

Objectives: As part of the collaboration between the U.S. Food and Drug Administration and Centers for Medicare & Medicaid Services, we assessed the safety of influenza vaccines recommended for 2022–2023 in the U.S. among Medicare beneficiaries 65 years and older by estimating the association between vaccination and four adverse events using a self-controlled case series design.

Methods: A self-controlled case series compared incidence rates of anaphylaxis, encephalitis/encephalomyelitis, Guillain-Barré Syndrome (GBS), and transverse myelitis following 2022–2023 seasonal influenza vaccinations (i.e., any, high-dose or adjuvanted) in event-specific risk and control intervals among U.S. Medicare beneficiaries 65 years and older. To reduce data lag, we used the Medicare Shared Systems Data capturing administrative claims data prior to final adjudication. The study period was August 1, 2022–June 2, 2023. For each adverse event, we used conditional Poisson regression to estimate incidence rate ratios (IRRs) and 95% confidence intervals (CIs) adjusted for event-dependent observation time, seasonality, and event misclassification where feasible. For adverse events with any statistically significant associations, we stratified results by concomitant vaccination status.

Results: Among 12.7 million recipients of 2022–2023 seasonal influenza vaccines, we observed 76 anaphylaxis, 276 encephalitis/encephalomyelitis, 134 GBS, and 75 transverse myelitis cases. Only rates of anaphylaxis were elevated in risk compared to control intervals. With all adjustments, an elevated, but non-statistically significant, anaphylaxis rate was observed following any (IRR: 2.40, 95% CI: 0.96–6.03), high-dose (IRR: 2.31, 95% CI: 0.67–7.91), and adjuvanted (IRR: 3.28, 95% CI: 0.71–15.08) influenza vaccination; anaphylaxis IRRs were 2.54 (95% CI: 0.49–13.05) and 1.64 (95% CI: 0.38–7.05) for those with and without any same-day concomitant vaccination, respectively.

Conclusions: Incidence rates of encephalitis/encephalomyelitis, GBS, or transverse myelitis were not elevated following 2022–2023 seasonal influenza vaccinations among U.S. Medicare beneficiaries 65 years and older. There was an increased rate of anaphylaxis following influenza vaccination that may have been influenced by concomitant vaccination.