Flu-like illness confers stroke risk in younger patients; vaccination may offer protection
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Influenza-like illness conferred increased odds of 30-day stroke in young patients, but vaccination was associated with lower risk compared with non-vaccination, according to data published in Stroke.
A similar analysis of middle-aged patients revealed similar odds of 30-day stroke tied to influenza-like illness; however, the protective effects of prior vaccination were more limited, according to the study.
“Vaccinating for influenza not only lowers your risk for influenza, but it also lowers the risk for stroke, particularly in younger adults. Influenza vaccination lowers the risk for stroke through a number of ways,” Amelia K. Boehme, PhD, MSPH, assistant professor of epidemiology in neurology at Columbia University, told Healio. “It can prevent someone from acquiring influenza, thereby preventing influenza-triggered stroke. People who are vaccinated for influenza tend to have a less severe form of influenza if they do have a breakthrough infection. Infection severity is associated with influenza-triggered stroke, so by lowering the severity of infection through the vaccine this reduces the risk for influenza-triggered stroke. Vaccinating regularly confers more immunity to influenza. The more years someone receives the influenza vaccine, the lower the risk for both influenza and stroke.”
Researchers evaluated the relationships between influenza-like illness in the prior 30 days to admission and vaccination in the prior year on stroke among young and middle-aged individuals. The MarketScan Commercial Claims and Encounters database was utilized to identify 24,103 cases of stroke in patients aged 18 to 44 years and 141,811 aged 45 to 65 years from 2008 to 2014. The stroke group was matched to controls based on age on admission date. Controls were patients with head trauma or ankle sprain at an inpatient or ED visit.
The primary outcome was ischemic and intracerebral hemorrhagic stroke.
Influenza-like illness and stroke in young patients
Researchers reported that patients aged 18 to 44 years experienced increased likelihood of stroke 30 days after influenza-like illness compared with controls (adjusted OR = 1.68; 95% CI, 1.51-1.86).
Influenza-like illness was associated with increased odds of 30-day stroke regardless of vaccination status (P for interaction = .16):
- vaccinated (aOR = 1.41; 95% CI, 1.08-1.85); and
- unvaccinated (aOR = 1.73; 95% CI, 1.55-1.94).
However, the odds of stroke were lower among patients with influenza-like illness and any vaccination in the year prior compared with their unvaccinated peers (aOR = 0.92; 95% CI, 0.87-0.99).
Influenza-like illness and stroke in middle-aged patients
Among patients aged 45 to 65 years, the adjusted likelihood of 30-day stroke risk was greater in patients with influenza-like illness compared with controls (aOR = 1.32; 95% CI, 1.26-1.38).
Researchers observed no effect of vaccination on stroke risk in patients with influenza-like illness compared with controls (aOR = 1; 95% CI, 0.97-1.02).
Although influenza-like illness was not associated with 30-day stroke among patients with any vaccination in the prior year (aOR = 1.07; 95% CI, 0.96-1.18), it was associated with odds of stroke among unvaccinated patients (aOR = 1.39; 95% CI, 1.32-1.47; P for interaction < .001).
“The hypothesis for why vaccination conferred less protection from stroke among those aged 45 to 65 years is likely because the risk factors and mechanisms for stroke start to change in mid-age with traditional stroke risk factors having a larger effect on stroke risk than the less traditional stroke risk factors,” Boehme told Healio. “The takeaway message here is evidence vaccinating against influenza reduces the risk for both influenza and stroke — as well as MI — but that was not evaluated in this particular study. With the incidence and prevalence of stroke increasing in people aged 18 to 45 years, identifying ways to reduce the risk for stroke is of utmost importance. Vaccinating against influenza is one way to reduce the risk.”
For more information:
Amelia K. Boehme, PhD, MSPH, can be reached at akb2188@cumc.columbia.edu.
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