The potential risk of Guillain-Barré syndrome (GBS) developing after receipt of Pfizer’s respiratory experimental syncytial virus (RSV) vaccine have prompted the U.S. Food and Drug Administration (FDA) to request that Pfizer conduct a post-marketing safety study if the vaccine is approved for use in the United States this spring.1 The RSV vaccine manufactured by GlaxoSmithKline (GSK) also suggested an elevated risk of GBS, which both the investigator and FDA concluded was “related to vaccination.”1
According to FDA briefing documents released earlier this month, two cases of GBS were discovered among nearly 20,000 vaccinated individuals during Pfizer’s clinical trials. There were no cases of GBS discovered in the placebo group of individuals who did not receive the vaccine. The briefing document states:
To assess the risk of Guillain-Barré syndrome and other immune-mediated demyelinating conditions among recipients post licensure, FDA has requested that the applicant propose a postmarketing safety study.2
GBS involves inflammation of the nerves in which the body’s immune system attacks healthy cells. Symptoms of GBS can range from brief weakness to partial or full body paralysis, which can be temporary or permanent.
GBS and multiple sclerosis (MS) both fall under the category of immune-meditated demyelinating conditions associated with “aberrant immune responses to myelin antigens.”3
According to the National Cancer Institute (NCI), antigens include viruses, toxins, or other foreign substances that induce immune responses.4
Of the two subjects in the Pfizer clinical trials who developed GBS, one man suffered a heart attack and was hospitalized prior to developing GBS symptoms seven days after RSV vaccination. The FDA does not view the heart attack as related to the RSV vaccine. The second patient was hospitalized 19 days after RSV vaccination following symptoms of sore throat, fatigue, and poor muscle control.1
Pfizer said that the GBS cases were possibly related to the vaccine but in its briefing document stated that both cases had other possible explanations, including the man’s heart attack and the woman having symptoms of an upper respiratory tract infection.1
The CDC’s Advisory Committee on Immunization Practices (ACIP) grappled with the association between the vaccine and GBS during a meeting held last earlier this month. CDC official Michael Melgar, MD told the committee that it is difficult to determine whether the new vaccines represent an actual safety concern or if they are linked to random events.1
FDA Advisers Recommend Approval of Pfizer and GSK RSV Vaccines
Following release and review of Pfizer’s data, FDA advisers have recommended that the agency approve both the Pfizer and GSK RSV vaccines for older individuals. The next step is for the FDA to license each vaccine followed by the CDC recommending the new shots before they become available to the public.5
Influenza and COVID-19 Shots Also Linked to GBS
GBS is thought to be linked to other vaccines, including the both the influenza and COVID-19 shots. According to the CDC’s website, the link between the influenza vaccine and GBS varies from season to season and that, while scientists have several theories about the cause, “the exact reason for this link remains unknown.”
The CDC website also states that they are continuously monitoring GBS cases associated with the COVID shots following evidence suggesting an increased risk in adults over 18 years old, who received Johnson & Johnson/Janssen’s adenovirus vectored Ad26.COV2.S COVID vaccine.6
Research articles from England and India both reported clusters of unusual variants of Guillain-Barre syndrome that were characterized by prominent bilateral facial weakness. Editors for the journal Annals of Neurology also reported an additional similar case in Boston following the Ad26.COV2.S vaccine. In addition, the editors analyzed cases of bilateral facial weakness reported to the U.S. Vaccine Adverse Events Reporting System (VAERS) and noted that five of eight GBS cases with bilateral facial weakness were reported by patients who received Ad26.COV2.S.7
RSV Vaccine for Pregnant Women Under Review
Pfizer also tested their RSV vaccine on pregnant women to see whether the protection can pass to babies in utero. The FDA is still reviewing the data for this population with a decision on approval expected to be made by August.8
Ross Kedl, PhD stated:
A reliable and efficacious vaccine against RSV for infants has been irritatingly elusive for many years, and it represents a significant unmet clinical need. This degree of protection could be a game-changer for newborns.8
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1 Kimball S. FDA says Guillain-Barre syndrome is possible risk of Pfizer’s RSV vaccine for older adults. CNBC Feb. 24, 2023.
2 Vaccines and related biological products advisory committee meeting. Respiratory Syncytial Virus Vaccine (Proposed trade name: Abrysvo). FDA Briefing Document. Feb. 28, 2023.
3 Hartung H. Immune-meditated demyelination. PubMed June 1993.
4 National Cancer Institute dictionary of cancer terms. Antigen. Mar. 6, 2023.
5 Bendix A. Paving the way for the world’s first RSV vaccine, FDA advisers recommend two different shots. NBC News Feb. 28, 2023.
6 U.S. Centers for Disease Control and Prevention. Guillain-Barre syndrome and vaccines. Feb. 6, 2023.
7 American Neurological Association. Guillain-Barré Syndrome Variant Occurring After COVID-19 Vaccines According to Two New Annals of Neurology Articles. Mar. 8, 2023.
8 Blackmer N. Pfizer’s RSV vaccine, given during pregnancy, could be available as early as this summer. MedPage Today Feb. 27, 2023.