THE risk of developing rare neurological complications is higher following a Covid infection than it is for either of the major vaccines used in the UK, according to the largest study of its kind to date.
Scientists found that the incidence of haemorrhagic stroke - a bleed on the brain - doubled in the first seven days after a positive test, and identified spikes in the rates of encephalitis and myelitis - inflammation of the brain and spinal cord respectively - as well as meningitis in people known to be infected.
However, the peer-reviewed study, which covered 32 million people in England with Scottish data used for comparison, also found an association between the AstraZeneca vaccine and a rare but occasionally life-threatening disorder called Guillain-Barré syndrome (GBS), which affects the nerves.
The rate was nearly four- times higher, however, among Covid patients.
READ MORE: What's really behind the NHS winter crisis?
Symptoms of GBS include numbness, pins and needles, and problems with coordination which tend to start in the hands and feet and spread into the limbs.
In severe cases, people can develop blood clots or difficulty moving, walking, breathing, and swallowing.
The condition is treatable and most people make a full recovery, but some are left with permanent disability and around one in 20 people die.
The findings, published in the journal Nature Medicine, provide the most robust evaluation to date of the association between the virus, vaccines and a range of neurological adverse events.
The study, led by Oxford University with input from researchers at Edinburgh University, covered the period from December 1 to May 31.
During this period, 20 million people in England received a first dose of the Oxford-AstraZeneca vaccine, 12 million received a first dose of the Pfizer-BioNTech vaccine, and two million people tested positive for Covid on a PCR test.
Adverse events following boosters, second doses or in children under 16 were excluded from the evaluation due to limited data, and only complications resulting in hospitalisation were included.
The analysis took into account incidence of neurological complications including encephalitis, Bell's palsy, stroke and Guillain-Barré occurring in the first 28 days after either vaccination or a positive PCR test for Covid.
The scientists stress that adverse events occurring in this 28 day window were not necessarily caused by the infection or vaccines. However, the timing points to evidence of a possible link.
This 'risk period' was then compared against a before and after baseline - excluding the 28 day periods either side of first vaccination or positive test - to gauge the normal frequency of these events.
This enabled the researchers - who are independent of the Oxford vaccine developers - to detect an 'excess', meaning that the frequency of complications was above baseline levels.
READ MORE: Plan B? Why Scotland's experience tells us it might not be enough
In relation to encephalitis, meningitis and myelitis, they found an excess of 123 cases per 10 million people following Covid infection. No association was found for either vaccine.
For Guillain-Barré syndrome, there was an excess of 38 cases per 10 million people following a first dose of the AstraZeneca vaccine, but that compared to an excess of 145 cases per 10 million people following a positive Covid test.
In relation to haemorrhagic stroke, the researchers detected an excess of 60 cases per 10 million people following the Pfizer vaccine.
However, they noted that this pattern was "not replicated" in the Scottish population dataset, but that this may have been due to the comparatively smaller sample size.
They also detected a doubling in the rate of haemorrhagic stroke in the first seven days after a positive Covid test, but found no overall excess when cases were analysed over the full 28 day period.
Initial vaccine clinical trials were not large enough to be able to detect very rare adverse neurological events – those that happen in less than one person out of 10,000.
Aziz Sheikh, a co-author on the paper and professor of primary care at Edinburgh University, said establishing an association between very rare complications and vaccines is important to help doctors recognise and act on them early.
He said it was the "largest and most robust study internationally to date" to put the AstraZeneca vaccine and Guillain-Barré syndrome into context against other vaccines and Covid.
READ MORE: Major Scottish study reveals that vaccines cut risk of death from Delta variant by over 90%
However, he stressed that in all cases these neurological adverse events were "so rare that we're having to report them per 10 million".
The findings also clearly emphasise that the risk from infection outweighs that from either vaccine type, said Prof Sheikh.
He added: "A key strength of this study was that we were able to replicate the analysis in Scotland’s national Covid-19 dataset.
"Overall, this provided strong support to the findings observed in the English dataset, namely that Covid-19 poses a greater risk of neurological adverse events than seen with wither the Oxford-AstraZeneca or Pfizer-BioNTech vaccines.
"This study demonstrates the very considerable power of UK data to investigate very rare safety concerns at pace and at scale.
"As far as we’re aware, no other country has this capability to do this and independently replicate findings."
More than four million people in Scotland have now received a first dose Covid vaccination, including 2.1m who had AstraZeneca.
However, one in 90 people are currently estimated to be carrying Covid infections with confirmed cases plateauing at around 2,500 per day.
Julia Hippisley-Cox, co-author and professor of clinical epidemiology and general practice at Oxford University, said: “We know the Covid-19 vaccines are very effective at reducing risks of severe outcomes from Covid-19 infection.
"Whilst there are some increased risks of very rare neurological complications associated with the Oxford-AstraZeneca vaccine, these are much smaller than the risks associated with Covid infection itself.”
Why are you making commenting on The Herald only available to subscribers?
It should have been a safe space for informed debate, somewhere for readers to discuss issues around the biggest stories of the day, but all too often the below the line comments on most websites have become bogged down by off-topic discussions and abuse.
heraldscotland.com is tackling this problem by allowing only subscribers to comment.
We are doing this to improve the experience for our loyal readers and we believe it will reduce the ability of trolls and troublemakers, who occasionally find their way onto our site, to abuse our journalists and readers. We also hope it will help the comments section fulfil its promise as a part of Scotland's conversation with itself.
We are lucky at The Herald. We are read by an informed, educated readership who can add their knowledge and insights to our stories.
That is invaluable.
We are making the subscriber-only change to support our valued readers, who tell us they don't want the site cluttered up with irrelevant comments, untruths and abuse.
In the past, the journalist’s job was to collect and distribute information to the audience. Technology means that readers can shape a discussion. We look forward to hearing from you on heraldscotland.com
Comments & Moderation
Readers’ comments: You are personally liable for the content of any comments you upload to this website, so please act responsibly. We do not pre-moderate or monitor readers’ comments appearing on our websites, but we do post-moderate in response to complaints we receive or otherwise when a potential problem comes to our attention. You can make a complaint by using the ‘report this post’ link . We may then apply our discretion under the user terms to amend or delete comments.
Post moderation is undertaken full-time 9am-6pm on weekdays, and on a part-time basis outwith those hours.
Read the rules hereLast Updated:
Report this comment Cancel