Flu Vaccine Linked to Reduced Stroke Risk

October has been pinpointed as the start of flu season in the United States. So if prevention of the contagious illness isn’t enough to convince patients to get their influenza vaccine, a new analysis involving stroke risk just might.

Respiratory infections, like the flu, can trigger a stroke. Previous research has linked the flu vaccine with reduced stroke risk; however, conclusions are conflicting. Zahid Asghar, PhD, from the University of Lincoln in the UK, and colleagues set out to investigate the relationship and found positive outcomes.

Data collected from the General Practice Research Database (GPRD) between September 2001 and May 2009, the analysis included participants who were at least 18 years of age.

“The incidence rate of stroke in fixed timed periods after influenza vaccination was compared with the incidence rate during a baseline period,” the authors described in the journal Vaccine.

A total of 17,853 eligible patients who received at least one influenza vaccination also experienced a stroke during the study period. Using conditional Poisson regression, the statistics were converted to incidence rate ratios (IRR). The greatest reduction in IRR was observed in those who received early vaccination — between September 1 and November 15 – when compared to later vaccinations received after that period. This could be because flu season is well underway by the time mid-November comes around.

The reductions in IRR were broken down:

• One to three days after vaccination: 55% reduction in IRR
• Four to seven days after vaccination: 36% reduction in IRR
• Eight to 14 days after vaccination: 30% reduction in IRR
• 15 to 28 days after vaccination: 24% reduction in IRR
• 29 to 59 days after vaccination: 17% reduction in IRR

“The incidence of stroke was significantly reduced in the first 59 days following influenza vaccination compared with the baseline period,” the team found.

The findings indicated that flu vaccines have the added benefit of reducing the risk of stroke, with the greatest protection being right after vaccination.

“This study supports previous studies which have shown a beneficial association of influenza vaccination for stroke prevention,” the authors confirmed.