Silver Spring, MD—The recombinant zoster vaccine (RZV) is highly effective against shingles, but a new study has found that older people who receive it have a slightly increased risk of developing Guillain-Barré syndrome (GBS).

A report in JAMA Internal Medicine discusses the results of an observational study of Medicare beneficiaries. Researchers from the FDA and other public health agencies and universities conducted a medical record–based, self-controlled analysis of GBS cases after RZV vaccination that involves two doses administered 2 to 6 months apart.

The study team calculated a rate ratio of 2.84 between the risk and control windows, which translates to an attributable risk of three cases per million doses of RZV, which is marketed as Shingrix.

The case series cohort study included two groups of beneficiaries aged 65 years or older: 849,397 RZV-vaccinated and 1.8 million beneficiaries who received zoster vaccine live (ZVL), which is marketed as Zostavax. The groups differed only slightly, with RZV recipients being 58% women and having a mean age of 74.8 years at first dose, while those receiving the ZVL vaccine were 60% women and had mean age of 74.3 years.

The focus was on events identified from 2.1 million eligible RZV-vaccinated beneficiaries aged 65 years or older. Researchers compared the relative risk of GBS after RZV versus ZVL. The study team used insurance claims and medical records to assess risk of GBS during a postvaccination risk window (Days 1-42) compared with a control window (Days 43-183).

Observation occurred from October 1, 2017, to February 29, 2020, with patients identified in the inpatient, outpatient procedural (including emergency department), and office settings using Medicare administrative data.

“In the cohort analysis we detected an increase in risk of Guillain-Barré syndrome among RZV vaccinees compared with ZVL vaccinees (rate ratio [RR], 2.34; 95% CI, 1.01-5.41; P = .047),” the researchers state. “In the self-controlled analyses, we observed 24 and 20 cases during the risk and control period, respectively. Our claims-based analysis identified an increased risk in the risk window compared with the control window (RR, 2.84; 95% CI, 1.53-5.27; P = .001), with an attributable risk of 3 per million RZV doses (95% CI, 0.62-5.64). Our medical record-based analysis confirmed this increased risk (RR, 4.96; 95% CI, 1.43-17.27; P = .01).”

The authors note that a slightly increased risk of GBS occurred during the 42 days following RZV vaccination in the Medicare population, with about three excess GBS cases per million vaccinations.

“Clinicians and patients should be aware of this risk while considering the benefit of decreasing the risk of herpes zoster and its complications through an efficacious vaccine, as risk-benefit balance remains in favor of vaccination,” the authors advise.

The FDA approved RZV to prevent herpes zoster (HZ) in adults aged 50 years or older on October 20, 2017. HZ, commonly known as shingles, and associated complications can cause significant morbidity, including long-term nerve pain and vision loss. The painful rash is caused by reactivation of the varicella zoster virus from latency and can be especially serious for elderly and immunocompromised patients.

Regulators considered results from randomized, placebo-controlled, clinical studies conducted in parallel in 18 countries; results demonstrated that RZV reduced the risk of developing HZ by 97.2% in participants aged 50 years or older and 89.8% in participants aged 70 years or older when compared with placebo.

After evaluation of available safety and efficacy data, the Advisory Committee on Immunization Practices gave RZV a preferential recommendation over ZVL  

The study notes that GBS, a rare, immune-mediated polyneuropathy leading to muscle weakness and paralysis, affects 3,000 to 6,000 people each year in the United States—i.e., one to two cases per 100?000 person-years.

When the CDC conducted postlicensure safety surveillance of RZV in the Vaccine Safety Datalink, it found that GBS incidence following RZV vaccination was higher than expected compared with a historical ZVL cohort, with a statistically significant rate ratio of 5.06.

That is what led to the study by the FDA, Centers for Medicare & Medicaid Services, and CDC.

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