Vaccines that protect against severe illness, death and lingering long Covid symptoms from a coronavirus infection were linked to small increases in neurological, blood, and heart-related conditions in the largest global vaccine safety study to date.
The viral-vector jabs were also tied to an increased risk of Guillain-Barre syndrome, a neurological disorder in which the immune system mistakenly attacks the peripheral nervous system.
More than 13.5 billion doses of Covid vaccines have been administered globally over the past three years, saving over 1 million lives in Europe alone. Still, a small proportion of people immunized were injured by the shots, stoking debate about their benefits versus harms.
The new research, by the Global Vaccine Data Network, was published in the journal Vaccine last week, with the data made available via interactive dashboards to show methodology and specific findings.
The research looked for 13 medical conditions that the group considered “adverse events of special interest” among 99 million vaccinated individuals in eight countries, aiming to identify higher-than-expected cases after a Covid shot. The use of aggregated data increased the possibility of identifying rare safety signals that might have been missed when looking only at smaller populations.
Myocarditis, or inflammation of the heart muscle, was consistently identified following a first, second and third dose of mRNA vaccines, the study found. The highest increase in the observed-to-expected ratio was seen after a second jab with the Moderna shot. A first and fourth dose of the same vaccine was also tied to an increase in pericarditis, or inflammation of the thin sac covering the heart.
Safety Signals
Researchers found a statistically significant increase in cases of Guillain-Barre syndrome within 42 days of an initial Oxford-developed ChAdOx1 or “Vaxzevria” shot that wasn’t observed with mRNA vaccines. Based on the background incidence of the condition, 66 cases were expected — but 190 events were observed.
Possible safety signals for transverse myelitis — spinal cord inflammation — after viral-vector vaccines were identified in the study. So was acute disseminated encephalomyelitis — inflammation and swelling in the brain and spinal cord — after both viral-vector and mRNA vaccines.
Seven cases of acute disseminated encephalomyelitis after vaccination with the Pfizer-BioNTech vaccine were observed, versus an expectation of two.
The adverse events of special interest were selected based on pre-established associations with immunization, what was already known about immune-related conditions and pre-clinical research. The study didn’t monitor for postural orthostatic tachycardia syndrome, or POTS, that some research has linked with Covid vaccines.
Exercise intolerance, excessive fatigue, numbness and “brain fog” were among common symptoms identified in more than 240 adults experiencing chronic post-vaccination syndrome in a separate study conducted by the Yale School of Medicine. The cause of the syndrome isn’t yet known, and it has no diagnostic tests or proven remedies.
The Yale research aims to understand the condition to relieve the suffering of those affected and improve the safety of vaccines, said Harlan Krumholz, a principal investigator of the study, and director of the Yale New Haven Hospital Center for Outcomes Research and Evaluation.
“Both things can be true,” Krumholz said in an interview. “They can save millions of lives, and there can be a small number of people who’ve been adversely affected.”

News
Small antibodies provide broad protection against SARS coronaviruses
Scientists have discovered a unique class of small antibodies that are strongly protective against a wide range of SARS coronaviruses, including SARS-CoV-1 and numerous early and recent SARS-CoV-2 variants. The unique antibodies target an [...]
Controlling This One Molecule Could Halt Alzheimer’s in Its Tracks
New research identifies the immune molecule STING as a driver of brain damage in Alzheimer’s. A new approach to Alzheimer’s disease has led to an exciting discovery that could help stop the devastating cognitive decline [...]
Cyborg tadpoles are helping us learn how brain development starts
How does our brain, which is capable of generating complex thoughts, actions and even self-reflection, grow out of essentially nothing? An experiment in tadpoles, in which an electronic implant was incorporated into a precursor [...]
Prime Editing: The Next Frontier in Genetic Medicine
By Dr. Chinta SidharthanReviewed by Benedette Cuffari, M.Sc. Discover how prime editing is redefining the future of medicine by offering highly precise, safe, and versatile DNA corrections, bringing hope for more effective treatments for genetic diseases [...]
Can scientists predict life longevity from a drop of blood?
Discover how a new epigenetic clock measures how fast you are really aging from just a drop of blood or saliva. A recent study published in the journal Nature Aging constructed an intrinsic capacity (IC) clock [...]
What is different about the NB.1.8.1 Covid variant?
For many of us, Covid-19 feels like a chapter we’ve closed – along with the days of PCR tests, mask mandates and daily case updates. But while life may feel back to normal, the [...]
Scientists discover single cell creatures can learn new behaviours
It was previously thought that learning behaviours only applied to animals with complex brain and nervous systems, but a new study has proven that this may also occur in individual cells. As a result, this new evidence may change how [...]
Virus which ’causes multiple organ failure’ found at popular Spanish holiday destination
British tourists planning trips to Spain have been warned after a deadly virus that can cause multiple organ failure has been detected in the country. The Foreign Office issued the alert on its dedicated website Travel [...]
Urgent health warning as dangerous new Covid virus from China triggers US outbreak
A dangerous new Covid variant from China is surging in California, health officials warn. The California Department of Public Health warned this week the highly contagious NB.1.8.1 strain has been detected in the state, making it the [...]
How the evolution of a single gene allowed the plague to adapt, prolonging the pandemics
Scientists have documented the way a single gene in the bacterium that causes bubonic plague, Yersinia pestis, allowed it to survive hundreds of years by adjusting its virulence and the length of time it [...]
Inhalable Nanovaccines: The Future of Needle-Free Immunization
The COVID-19 pandemic highlighted the need for adaptable and scalable vaccine technologies. While mRNA vaccines have improved disease prevention, most are delivered by intramuscular injection, which may not effectively prevent infections that begin at [...]
‘Stealthy’ lipid nanoparticles give mRNA vaccines a makeover
A new material developed at Cornell University could significantly improve the delivery and effectiveness of mRNA vaccines by replacing a commonly used ingredient that may trigger unwanted immune responses in some people. Thanks to [...]
You could be inhaling nearly 70,000 plastic particles annually, what it means for your health
Invisible plastics in the air are infiltrating our bodies and cities. Scientists reveal the urgent health dangers and outline bold solutions for a cleaner, safer future. In a recent review article published in the [...]
Experts explain how H5 avian influenza adapts to infect more animals
A new global review reveals how rapidly evolving H5 bird flu viruses are reaching new species, including dairy cattle, and stresses the urgent need for coordinated action to prevent the next pandemic. Since its [...]
3D-printed device enables precise modeling of complex human tissues in the lab
A new, easily adopted, 3D-printed device will enable scientists to create models of human tissue with even greater control and complexity. An interdisciplinary group of researchers at the University of Washington and UW Medicine [...]
Ancient DNA sheds light on evolution of relapsing fever bacteria
Researchers at the Francis Crick Institute and UCL have analyzed ancient DNA from Borrelia recurrentis, a type of bacteria that causes relapsing fever, pinpointing when it evolved to spread through lice rather than ticks, and [...]