RSV Vaccine Linked to Rare Nervous System Disorder

Post-marketing data shows a higher-than-expected number of Guillain-Barre syndrome cases among older adults receiving Pfizer's Abrysvo RSV vaccine.

Respiratory syncytial virus (RSV) is a common respiratory virus that can cause severe illness in infants and older adults. Because of the risks for people in these age groups, the Centers for Disease Control and Prevention (CDC) recommends that adults ages 60 years and older discuss getting one dose of the RSV vaccine with their healthcare provider.

The agency also recommends that pregnant individuals receive one dose of the RSV vaccine from week 32 through week 36 of pregnancy to prevent the illness in infants.

According to the CDC, as of February 3, an estimated 9,651,749 RSV vaccines have been administered to adults 60 years and older in the United States. Research published in May 2023 estimated that RSV vaccines could potentially prevent 154,728 symptomatic RSV cases, 3,688 hospitalizations, and 502 deaths over three years.

Currently, there are two RSV vaccine options available — Abrysvo, made by Pfizer, and Arexvy, manufactured by GSK.

While side effects that commonly occur following RSV vaccination include injection site reactions, fatigue, and headache, other more serious adverse events have been reported.

For example, cases of Guillain-Barré syndrome (GBS) — a potentially life-threatening condition in which the immune system attacks the peripheral nerves — were reported in RSV vaccine clinical trial participants. As a result, both vaccines list GBS as an adverse event on their labels.

Still, the CDC says it's unclear whether the vaccine caused GBS.

However, new post-marketing safety data presented at an Advisory Committee on Immunization Practices (ACIP) meeting on February 29 shows higher-than-expected GBS cases among older adults following RSV vaccination.

During the meeting, health officials presented RSV vaccine safety monitoring data from V-safe, the Vaccine Adverse Event Reporting System (VAERS), and Vaccine Safety Datalink (VSD).

According to VAERS data, as of February 16, 23 verified cases of GBS occurred in older adults within 22 days after receiving an RSV vaccine, resulting in one death.

While estimates suggest that two out of every 1 million people experience GBS after receiving a vaccine, after analyzing the data, health officials found that the rate of GBS among those vaccinated with Pfizer's Abrysvo was 4.6 cases per million. The GBS rate following GSK's shot was lower than two out of 1 million.

VAERS data also showed that 34 deaths and 58 cases of atrial fibrillation were reported among people 60 years or older after RSV vaccination.

Due to the potentially concerning GBS safety signals, VSD will continue to monitor the safety of RSV vaccines in older adults. In addition, a formal sequential safety analysis of RSV vaccines will begin in March 2024.

According to an Associated Press report, Pfizer Vice President Reema Mehta says the company is committed to the continuous monitoring and evaluation of the safety of Abrysvo and is conducting four studies to investigate the possibility of vaccine-related GBS.

Health officials say that while these potential links between RSV vaccines and GBS need more investigation, the benefits from vaccination, such as lower rates of infection, hospitalization, and death, outweigh any possible risks.