Does the Flu Shot Raise VTE Risk?

The influenza vaccine is not associated with an increased risk for venous thromboembolism (VTE) in adults age 50 years or older, according to a recent study. However, the risk for VTE after vaccination is higher among individuals who smoke.

Influenza-like illness and inflammation are established risk factors for VTE, which includes deep vein thrombosis (DVT) and pulmonary embolism (PE). However, little data exists on the potential association between the influenza vaccination and the risk of VTE.
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For their study, the researchers identified 1488 presumptive cases of VTE among adults age 50 years or older who had received the influenza vaccine with or without pandemic H1N1 between September and December from 2007 to 2012. Patient data was obtained from the Vaccine Safety Datalink (VSD)

Diagnostic codes, diagnostic tests, and oral anticoagulant prescriptions were used to identify presumptive cases of VTE among VSD participants. Medical record review was performed to validate potential cases of VTE. Additionally, the rate ratio of VTE incidence was determined among confirmed cases for the risk window 1 to 10 days following vaccination relative to all other person-time from September to December.

Of the 1488 presumptive cases of VTE, 508 were reviewed, 492 were confirmed, and 396 were included in the analysis. Results indicated that the influenza vaccine was not associated with a higher risk of VTE in the 1 to 10 days following vaccination, compared with the control period.

Results were similar when all-person time was censored prior to vaccination. However, according to a post hoc analysis, the risk for VTE after vaccination was higher in current tobacco smokers.

The researchers also noted that no clustering of VTE had occurred in the 1 to 42 days post-vaccination.

“Overall, there was no evidence that inactivated influenza vaccine was associated with VTE in adults [age 50 years or older],” the researchers concluded. “An increased risk was found among current smokers in a post hoc analysis. These findings are consistent with previous research and support the safety of annual vaccination in this population.”

—Christina Vogt

Reference:

Vickers ER, McClure DL, Naleway AL, et al. Risk of venous thromboembolism following influenza vaccination in adults aged 50 years and older in the Vaccine Safety Datalink. Vaccine. 2017;35(43):5872-5877. doi:10.1016/j.vaccine.2017.08.086.