An elevated risk of stroke occurs after shingles infection, but treatment with antivirals and vaccine does not appear to mitigate the situation, according to a new study.

The study published in Neurology sought to determine whether increased risk of acute ischemic stroke (AIS) following herpes zoster (HZ) might be modified by immunization with zoster vaccine live (ZVL) and antiviral treatment after onset of symptoms.

Researchers from the CDC’s Division for Heart Disease and Stroke Prevention said that the better strategy was preventive vaccination. Preliminary findings were presented last year at the American Stroke Association’s International Stroke Conference 2019 in Honolulu, Hawaii. 

Included in the study were 87,405 Medicare fee-for-service beneficiaries aged 66 years and older diagnosed with HZ and AIS from 2008 to 2017. The study team employed a self-controlled case series design to examine the association between HZ and AIS and estimated incident rate ratios (IRR) by comparing incidence of AIS in risk periods versus control periods. 

In an effort to better examine effect modification by ZVL and antiviral treatment, researchers classified beneficiaries into four mutually exclusive groups:

1) No vaccination and no antiviral treatment 
2) Vaccination only
3) Antiviral treatment only 
4) Both vaccination and antiviral treatment. 

The researchers tested for interaction to examine changes in IRRs across the four groups. They noted that 22.0%, 2.0%, 70.1%, and 5.8% of the patients were in groups 1 to 4, respectively.

Results indicate that IRRs in 0 to 14, 15 to 30, 31 to 90, and 91 to 180 days following HZ were 1.89 (95% confidence interval [CI],1.77-2.02), 1.58 (95% CI,1.47-1.69), 1.36 (95% CI,1.31-1.42), and 1.19 (95% CI,1.15-1.23), respectively. 

“There was no evidence of effect modification by ZVL and antiviral treatment on AIS (p=0.067 for interaction),” the authors write. “The pattern of association between HZ and risk for AIS was largely consistent across age group, sex, and race.”

The study found that stroke incidence increased by 61% within 14 days after shingles onset and remained elevated 6 months afterward, although it diminished over time.

“Risk of AIS increased significantly following HZ, and this increased risk was not modified by ZVL and antiviral treatment,” the researchers concluded. “Our findings suggest the importance of following recommended HZ vaccination in prevention of HZ and HZ-associated AIS.”

In this study, researchers examined the effect of the Zostavax shingles vaccine because Medicare data were not yet available for the Shingrix recombinant zoster vaccine. The presentation pointed out that Zostavax efficacy declines over time, with protection from shingles lasting only about 5 years. 
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