How serious is risk of stroke with updated Pfizer vaccine?

Health officials say there is no proven link yet - and benefits of vaccination heavily outweigh potential dangers

A dose of the Pfizer-BioNTech vaccine is administered. Authorities have played down the potential risk of stroke linked to the shot. Photo: Reuters

Health officials in the US have identified a possible link between the updated coronavirus vaccine made by Pfizer and BioNTech and a type of brain stroke in the elderly.

The Pfizer-BioNTech messenger RNA (mRNA) vaccine — the original version of which was first approved by US medical regulators in August 2021 — has been one of the world's most effective and widely used shots.

Here we look at the evidence available and consider what medical experts in the UAE and internationally are saying in the light of recent findings.

What are the safety concerns?

The US Centres for Disease Control and Prevention, commonly referred to as the CDC, and the Food and Drug Administration have identified what could be an increased risk of ischaemic strokes in people 65 and older who have had one of Pfizer’s updated boosters or bivalent shots.

The latter protect against more than one form of the coronavirus, in this case the original strain plus the Omicron BA.4 and BA.5 variants.

Ischaemic strokes are, according to the UK’s National Health Service, the most common type, which develop when a clot blocks blood flow in arteries leading to the brain.

The CDC’s vaccine database indicates that over-65s could face an increased risk of this type of stroke in the three weeks immediately after being given the updated shot, compared to the subsequent three-week period.

The organisations said they wanted to share the information with the public even though it was "very unlikely" the possible link to strokes "represents a true clinical risk".

Subsequent analysis of other vaccine databases have not highlighted an increased risk of strokes with the bivalent Pfizer-BioNTech shot.

What do US authorities say?

The CDC stated that "no change in vaccination practice is recommended", with the potential safety risks said to be heavily outweighed by the benefits of inoculation.

"CDC continues to recommend that everyone six months of age and older stay up-to-date with Covid-19 vaccination; this includes individuals who are currently eligible to receive an updated (bivalent) vaccine," a CDC statement said.

"Staying up-to-date with vaccines is the most effective tool we have for reducing death, hospitalisation and severe disease from Covid-19, as has now been demonstrated in multiple studies conducted in the United States and other countries."

The two companies behind the vaccine, the US pharmaceutical giant Pfizer and the German biotechnology firm BioNTech, also insisted their product was safe.

"There is no evidence to conclude that ischaemic stroke is associated with the use of the companies' Covid-19 vaccines," a joint statement said.

Officials said there was no evidence that the updated form of another mRNA Covid-19 shot, produced by Moderna, was linked to an increased risk of strokes.

What do doctors say?

Doctors in Dubai also said the benefits of vaccination outweighed the risks, but that high-risk patients with hypertension and heart ailments should be aware.

“Only time will prove what is the efficacy and what are the secondary complications of the vaccines,” Dr Sanjay Paithankar, head of the Right Health group, which has more than 58 medical clinics in the UAE, told The National.

He said the data on increased instances of stroke could not be correlated directly to the use of the vaccines and could be linked to the disease itself.

“There is no need to panic,” Dr Paithankar said. “It will be difficult to prove that the incidents are correlated to use of the vaccine. Only time will tell.

“But yes, the benefits outweigh any risks. The vaccines have saved humanity, people would have been wiped out without vaccines.”

What other health risks have been linked to Covid-19 shots?

The health benefits of vaccination against Covid-19 heavily outweigh the risks, but there have been other concerns linked to some shots.

There have been reports of a small number of adults under 45 having an ischaemic stroke in the month after they received the Oxford-AstraZeneca Covid-19 drug, which is a viral vector vaccine, not an mRNA.

That shot has also been associated with a small number of cases in which people suffered blood clots and a different type of stroke, mostly affecting veins in the brain.

The mRNA inoculation has also been linked to a limited numbers of cases in which young people, mostly boys and young men, experienced myocarditis, inflammation of the heart muscle, or pericarditis, an inflammation of the outer lining of the heart.

Patients usually responded well to treatment and when the link emerged, the CDC did not recommend changes to vaccination.

With the latest issue, the CDC and the FDA will continue to evaluate data and the issue will be discussed at a meeting of the FDA’s vaccines and related biological products advisory committee next Thursday.