Guillain-Barré reports after the RSV vaccine ran above the expected rate

The FDA licensed Arexvy and Abrysvo in May 2023 to prevent RSV
lower respiratory tract disease in adults aged 60 and over. **In the trials,
Guillain-Barré syndrome was identified as a potential safety concern.**

This report is what the safety monitoring found afterwards.

The finding

**Reports of Guillain-Barré syndrome were more common than expected background
rates:**

Findings are consistent with those from the trials — the signal seen
before licensure is still there after it.

How to read those numbers

A report is not a confirmed case caused by the vaccine; passive surveillance
collects what clinicians send in. But "more common than expected background
rates" is the comparison that matters: more reports arrived than would be
expected from the rate at which Guillain-Barré occurs anyway in this age
group.

Set against that, the scale: 4.4 per million doses. Guillain-Barré is serious
and it is rare here, and RSV kills thousands of older adults each year.

What follows

**ACIP recommends that adults aged 60 and over may receive one dose of RSV
vaccine** — may, a shared clinical decision rather than a blanket
recommendation, which is how a benefit-risk judgement of this shape is usually
expressed.

**Population-based surveillance will evaluate the potential risk for GBS to
guide ACIP recommendations.**

Passive reports raise a question; population-based surveillance answers it,
because it has a denominator. The recommendation is explicitly provisional on
that work.

*Source: Hause AM, Moro PL, Baggs J, et al. Early Safety Findings Among
Persons Aged ≥60 Years Who Received a Respiratory Syncytial Virus Vaccine —
United States, May 3, 2023–April 14, 2024. MMWR, Centers for Disease Control
and Prevention.*