In this study, the researchers used a within-person study design to quantify any short-term increased risk of stroke and myocardial infarction [MI] after herpes zoster and to assess whether the herpes zoster vaccination causes any changes to the hypothesis.
The researchers first obtained administrative claims data from older US Medicare beneficiaries, where the source population included Medicare beneficiaries aged 65 years and above enrolled in Medicare Parts A, B and D which were hospital insurance, supplemental medical insurance and prescription drug coverage respectively. These patients either had a zoster diagnosis and a CMS Chronic Conditions Data Warehouse flag for acute MI or stroke/transient ischemic attack, or both.
They identified the earliest recorded zoster episode of each patient as well as vascular events during the observation period. Then, they excluded individuals with evidence of vascular events or herpes zoster prior to the observation period. They also excluded patients with only secondary inpatient diagnoses since these events (MI and shingles) were not the primary reason for hospitalisation and hence may have occurred at any time during their hospital stay.
Like the previous article, the researchers also defined herpes zoster by ICD-9-CM diagnostic code 053x with an antiviral prescription in the 7 days before or after diagnosis.
For the stroke analyses,they excluded individuals with subarachnoid hemorrhage or are at risk, patients with aneurysms in the circle of Willis (pathway of connecting blood vessels that supply blood to the brain) or arteriovenous malformations and encephalitis diagnoses recorded up to 12 months after the stroke.
Age-adjusted incidence ratios (IRs) for stroke and MI were calculated using conditional Poisson regression.
In the first week after zoster diagnosis, a 2.4-fold increase in ischemic stroke rate and a 1.7-fold increase in MI rate was seen. These symptoms were seen to gradually resolve over 6 months.
Vaccination did not appear to affect the hypothesis, however as only a few of the individuals in this study were vaccinated, this limited the study’s power to determine if vaccination was a factor at play.
Stroke and MI rates are temporarily increased after exposure to herpes zoster. However, the researchers found no evidence for a role of zoster vaccination in these associations.