People run a greater risk of suffering neurological complications if they contract Covid than if they have a Covid vaccine, a new study has concluded.

Researchers undertook a self-controlled case series study to investigate hospital admissions from neurological complications in the 28 days after a first dose of the Astra/Zeneca vaccine; the Pfizer/BioNTech vaccine; and a positive Covid test respectively.

Their paper, published in the journal Nature Medicine, found that there was an increased risk of Guillain-Barré syndrome and Bell’s palsy related to the AZ vaccine, while the Pfizer vaccine increased the risk of hemorrhagic stroke.

However, the researchers concluded that: ‘There was a substantially higher risk of all neurological outcomes in the 28 days after a positive [Covid] test.’

The researchers, from the University of Oxford, analysed healthcare records of over 32 million people across England to reach their conclusion.

The risk of developing a neurological condition from the vaccines was ‘substantially lower’ than the risk presented by contracting Covid, said Martina Patone, medical statistician at the Nuffield Department of Primary Care Health Sciences at the University of Oxford, and co-lead author.

‘We estimate 145 excess cases of Guillain-Barre syndrome per 10 million people in the 28 days after a positive SARS-CoV-2 test, compared to 38 per 10 million for those who received the ChAdOx1nCoV-19 vaccine,’ she said.

The researchers warn, however, that there could be more cases of milder neurological disease, as the study only included hospital admissions and deaths.

The study does not shed light on how second doses of the Pfizer and AZ vaccines affect risk – however, researchers say these findings can help inform clinicians.

Lahiru Handunnetthi, clinical lecturer at the Nuffield Department of Clinical Neurosciences, University of Oxford, and co-lead author of the paper, said awareness of the risks ‘will be important for patient care during mass vaccination programmes across the world’.

Julia Hippisley-Cox, co-author and professor of clinical epidemiology and general practice at the University of Oxford, said: ‘These very rare conditions are very important to spot to ensure that clinicians know what to look for, aid earlier diagnosis, and inform clinical decision making and resource management.’

A version of this story first appeared on our sister website, Pulse.