People who receive Pfizer’s RSV vaccine for older adults should be monitored for Guillain-Barre syndrome, after two individuals developed the nervous system disorder following vaccination, according to clinical trial results published in the New England Journal of Medicine.
The scientists concluded that the vaccine was effective in preventing lower respiratory tract illness in adults aged 60 and older without any evident safety concerns.
However, they highlighted the Guillain-Barre cases as a potential cause for concern moving forward.
“If RSVpreF vaccine is approved and recommended, these adverse events warrant close monitoring in future studies and with real-world data and postmarketing surveillance,” the scientists wrote.
Guillain-Barre syndrome is a rare disorder where the body’s immune system mistakenly attacks the nerves.
Symptoms can range from brief weakness to paralysis, according to the National Institutes of Health. Most people recover, even from severe cases.
The scientists’ recommendation for close monitoring of a possible link between the vaccine and Guillain-Barre aligns with the position of the Food and Drug Administration (FDA).
The FDA has requested Pfizer to include Guillain-Barre as an “important potential risk” of the vaccine and to develop a safety study to monitor for potential cases if the shot is approved in May. Pfizer has agreed to conduct the safety study.
The FDA’s independent advisors endorsed the vaccine in February, although there was significant dissent during the meeting.
Seven advisors stated the safety data was sufficient for approval, while four said it was not, and one abstained.
In the New England Journal of Medicine article, the scientists noted that the two cases occurred in patients who were in an age group with an increased risk of developing Guillain-Barre.
They also mentioned that factors other than the vaccine could have caused the individuals to develop the syndrome.
However, the FDA stated that it views the Guillain-Barre cases as potentially related to the vaccine because the patients developed the syndrome shortly after receiving the shot, according to briefing documents published in February.
Pfizer concluded that the cases were unrelated, and the clinical trial’s data monitoring committee did not identify any safety concerns with the vaccine.
Pfizer’s shot is in contention to become the first RSV vaccine ever approved for older adults.
RSV kills between 6,000 and 10,000 seniors annually, according to the Centers for Disease Control and Prevention (CDC). It also causes 60,000 to 160,000 hospitalizations among this age group each year.
The vaccine was 86% effective at preventing lower respiratory tract illness with three or more symptoms and 66% effective at preventing the illness with two or more symptoms, according to the results published in the New England Journal of Medicine. The shot is administered as a single, 120-microgram dose.
While the vaccine shows promise in reducing hospitalization and death from RSV among seniors, the FDA’s advisors were concerned about the Guillain-Barre cases during their February meeting.
Dr. Hana El Sahly, the FDA committee chair, stated that Guillain-Barre has an incidence of about 1 in 100,000 among people aged 60 and older. But in the vaccine trial, the rate was closer to 1 in 9,000.
“So this is major if we take it at this level,” El Sahly said. She acknowledged there’s still uncertainty about what the actual rate of the disease would be among vaccine recipients.
“But nonetheless, it’s significant in terms of incidence,” she said of the two cases. The advisors who endorsed the vaccine also emphasized that safety monitoring will be crucial after any potential FDA approval.
A 66-year-old man in the U.S. developed Guillain-Barre, and a woman of the same age in Japan was diagnosed with a variant of the syndrome called Miller Fisher.
The patients developed symptoms seven and eight days after vaccination, respectively.
The man had a history of hypertension and had suffered a heart attack shortly before he was diagnosed with Guillain-Barre, and the woman had a history of diabetes. The FDA does not view the heart attack as related to the vaccine.
The man’s symptoms were resolving six months after onset, and the woman’s symptoms resolved completely three months after onset.
