Increased risk of neurological complications after Covid vaccine, study finds, though cases mostly benign

A new study has found that there is an increased risk of neurological complications following Covid vaccination, and while in most cases these have a benign nature, caution should be used when administering the vaccines to vulnerable people, such as to those who have allergies.

The study, published in the journal Vaccines, used a sample size of 19,096 people who had been vaccinated in July 2021, and was published in the medical journal at the end of October.

“Clinicians should be aware that several neurological complications may commonly occur after COVID-19 vaccines, but in most cases, these have a benign nature, caution should be used when administering COVID-19 vaccines to vulnerable people, such as to those who suffer from allergies. We strongly believe that our findings are relevant for public health regarding the safety of vaccines in a large cohort”, researchers concluded.

The Italian population-based study evaluated the neurological complications after a first and/or second dose of Covid-19 vaccine, and the factors potentially associated with those adverse effects. Involving a cohort aged 18 and older who had received two vaccine doses at a vaccination centre in Milan, Lombardy in July of 2021. 

Researchers from the Institute of Molecular Bioimaging and Physiology at the National Research Council, Sleep Disorders Center, Division of Neuroscience at the San Raffaele Scientific Institute, the School of Medicine at Vita-Salute San Raffaele University, and the San Raffaele Scientific Institute were behind the study.

The sample took part in a questionnaire to capture neurological effects, along with onset and duration, with researchers finding that almost one third of participants – 6,044 people – reported suffering an array of neurological complications shortly after receiving a Covid vaccine.

 Complications reported by respondents included insomnia, muscle spasms, headaches, paresthesia and vertigo – with researchers stating that further investigation would be needed to determine the exact cause, as well as long-term effects, of such complications.

In their findings, authors noted that between March to August 2021, none of the participants in the study were hospitalised and/or died of severe complications related to COVID-19 vaccinations. 

Authors of the population based study noted how the first concern regarding the potential neurological complications post-vaccinated dated from September 202, when AstraZeneca/Oxford University reported “severe inflammation” of the spinal cord. 

Authors noted that following on from this, in May of 2021, the American Neurology Academy provided the first report on the common neurological complications after COVID-19 vaccines.

They highlighted how, in December 2021, a large population-based study identified rare neurological adverse effects after the first dose of a Covid vaccine, noting how “severe and unexpected post-vaccination complications have also recently been detected.”

Authors noted: “They include cerebral venous sinus thromboses occurring especially in females after adenovector-based vaccination as well as Guillain-Barré syndrome, facial palsy, other neuropathies, encephalitis, meningitis, myelitis and autoimmune disorders.”

“However, these events were found in isolated case reports or small series,” they continued. “On the other hand, it was demonstrated that the risk of severe neurological complications may be greater following a positive SARS-CoV-2 test.”

They further noted that a “wide spectrum” of mild,  transient and self-limiting neurological complications including fever and chills, headache, fatigue, myalgia and arthralgia, or local injection site effects has been also reported following COVID-19 vaccination.

However, authors said that “little is yet known about the neurological complications after both doses of COVID-19 vaccines, as well as about their nature.”

Those who participated in the study, from the vaccination hub of Novegro (Milan, Lombardy) had primarily received the Pfizer vaccine – making up 80 per cent of the complete sample size, while the remaining 20 per cent had taken the Moderna vaccine. Authors noted how both vaccines had been administered around the world.

The study reported, regarding ‘severe’ neurological complications, that one female participant attended an emergency room for sudden difficulty walking, while another male participant reported sudden memory loss, lasting one day. Another participant, a young man, had facial paresis – with all of the cases occurring after the second dose of a vaccine. However, authors said that aside from the single cases of complications listed, there were no severe adverse events self-reported by the cohort. 

“Additionally, the digital healthcare system matching also confirmed this, since none of the 19,108 subjects of our vaccinated cohort (symptomatic and not symptomatic) was hospitalised in neurological and/or non-neurological clinics and/or died in the observational period ranging from March to August 2021 for severe complications related to the COVID-19 vaccination,” researchers said.

Authors said that the AstraZeneca vaccine produced an increased risk of tremors, insomnia, tinnitus, muscle spasms and headache; while the Moderna vaccine meant an increased risk of taste and smell alterations, vertigo, diplopia, sleepiness, parethesias and dysphonia. The Pfizer vaccine, the study showed, presented an increased risk of cognitive fog.

Outlining the study’s limitations, authors said their  results “should be interpreted with caution” because of a possible overestimation of neurological events resulting from the self-reported symptoms. 

Secondly, “we evaluated the risks associated with the first and second doses of the vaccine; however, the data concerning the second dose were limited, thus representing a potential bias in the study. Possible misunderstandings of the study and/or inabilities to send the subacute questionnaires may have occurred,” they said.

The study identified a specific neurological risk profile for each vaccine and a clinical profile for those more vulnerable to develop neurological complications after taking a Covid-19 vaccine. Researchers said that clinicians ‘should be aware’ that several neurological complications may commonly occur after Covid-19 vaccines – but that ‘in most cases,’ these have a benign nature. 

They added that caution should be used when administering Covid-19 vaccines to vulnerable people, such as those who suffer from allergies. Authors said they were of the strong belief that their findings were relevant for public health regarding the safety of Covid vaccines in a large cohort.