FDA says Pfizer’s new RSV vaccine for older adults may trigger painful and potentially deadly Guillain-Barre syndrome in one in 10,000 patients

Pfizer’s new RSV vaccine for older adults may trigger the potentially deadly Guillain-Barre syndrome, the Food and Drug Administration (FDA) has warned.

In clinical trials, two participants in their 60s developed the condition that can also cause crippling pain, muscle weakness and paralysis.

One of the patients recovered after three months, but the second took six months to return to normal. They were among 20,000 adults who got the shot. 

Among the control group who did not get the vaccine, there were no cases of GBS, which has prompted the FDA to ask Pfizer to conduct a safety review before approving the vaccine.

Pharmaceutical giants are developing a vaccine against respiratory syncytial virus (RSV), a winter respiratory bug that kills up to 10,000 adults over 65 years old every year. There is currently no shot against the disease available. 

There are currently no vaccines available for RSV. The disease is common with cases surging this year in the absence of Covid restrictions (pictured). Older adults are more at risk from the disease because they have weaker immune systems

Guillain-Barre sees the immune system go haywire and start to attack nerve cells, triggering symptoms including muscle pain, numbness and pins and needles.

It was also recorded during trials of a rival RSV vaccine made by UK-based pharmaceutical giant GSK. 

The condition has also previously been reported in people who got AstraZeneca’s Covid vaccine, which was not approved for use in the US.

One of the patients to develop the syndrome in Pfizer’s trial was an American man in his 60s with a history of high blood pressure.

He suffered lower back pain eight days after vaccination and experienced weakness in his legs on the 14th day. 

After suffering a fall, the man was hospitalized and subsequently diagnosed with the syndrome. His symptoms resolved in six months.

The patient also suffered a heart attack, but the FDA said this was not related to the RSV vaccine.

In the second case, a woman in her 60s in Japan with a history of type 2 diabetes developed a variant of the syndrome, called Miller-Fisher syndrome.

Miller-Fisher tends to affect the upper body first, whereas Guillain-Barre typically affects the lower body and then spreads upwards. 

She experienced fatigue nine days after vaccination and, on day ten, suffered from a sore throat and poor muscle control.

She was hospitalized 19 days after vaccination. Her symptoms cleared within three months.

Official documents released by the FDA read: ‘Given the temporal association and biological plausibility, FDA agrees with the assessments of the investigators that these events were possibly related to study vaccine.

‘Therefore, [Guillain-Barre] is being considered an important potential risk.’

Guillain-Barre is a rare neurological condition in which the immune system misfires and starts to attack the body’s nerves.

In severe cases, this can cause paralysis, breathing difficulties, blood clots and fatalities. It can also leave patients suffering pain.

It normally appears within days or weeks of a respiratory or digestive tract infection. Previous research has linked both Covid and RSV infections with the syndrome, and previous vaccines.

There’s no cure for the syndrome, but treatments are available that can speed recovery. 

About one to two Americans per 100,000 people have Guillain-Barre syndrome, estimates suggest. Among the over-60s, this rises to up to one in 33,000 people.

The documents were released ahead of a meeting to approve the vaccine next week run by the Vaccines and Related Biological Products Advisory Committee (VRBPAC) —  which reviews the safety and effectiveness of vaccines. 

Pfizer has agreed to carry out the safety review of its phase three clinical trial, the final stage before approval.

But in a briefing document, the company suggested there may have been other explanations for the reactions.

They add that the shot is a ‘well tolerated and safe vaccine, with a benefit-to-risk ratio that is favorable.’

There is currently no vaccine available against RSV, which spiked this winter in the absence of Covid restrictions.

RSV is a common infection that causes cold symptoms that disappear within a few days.

But it is more dangerous in older adults who have weaker immune symptoms and, in severe cases, can leave them with pneumonia and even death.

The phase three clinical trials showed Pfizer’s jab was 66.7 percent effective at preventing moderate lower respiratory tract illness with two or more symptoms.

It was also 85 percent effective at preventing severe illness.

This was similar to the shot being developed by GSK, which was 94.1 percent effective against severe lower respiratory tract disease and 82.6 percent effective in preventing illness overall.

Cases of potential Guillain-Barre syndrome were also recorded in this trial, but there was insufficient evidence to confirm a diagnosis. 

Data from both vaccines was discussed Thursday during a meeting of the CDC’s Advisory Committee on Immunization Practices. 

They concluded that the vaccines ‘demonstrated significant efficacy against lower respiratory tract illness caused by RSV among older adults’.

But they added that ‘post-licensure surveillance for both safety and vaccine effectiveness will be critical’ should the jabs be approved by the FDA.