Covid vaccines have been linked to a small increase in heart, blood and neurological diseases, according to the largest global study of its kind.
An international coalition of vaccine experts looked for 13 medical conditions among 99 million vaccine recipients in eight countries to identify higher rates of these conditions after receiving the shots.
They confirmed that the shots made by Pfizer, Moderna and AstraZeneca are linked to a significantly higher risk of five medical conditions, including a nerve-wracking condition that causes people to have trouble walking or thinking.
But the study also warned of several other conditions that they said warranted further investigation, including links between brain swelling and the Moderna shot.
Still, the team says the absolute risk of developing either of these conditions remains small. For example, 13 billion doses of vaccines have been administered and there have only been 2,000 cases of all conditions.
The researchers identified twelve conditions that could be linked to different Covid vaccines. Among the most troubling were inflammation of the heart muscle and swelling of the brain
The injections were linked to a range of diseases, but the risk was still relatively small
Dr. Harlan Krumholz, director of the Yale New Haven Hospital Center for Outcomes Research and Evaluation and lead researcher behind the study, said, “Both things could be true.
“They can save millions of lives, and there may be a small number of people who are negatively affected.”
It is estimated that Covid vaccines have prevented more than 19 million deaths worldwide, including three million in the US alone.
One of their discoveries was a twofold increase in the risk of a neurological condition known as Guillain-Barre syndrome, an autoimmune disease in which the immune system attacks the body’s peripheral nervous system, leading to damage to the protective covering around nerve cells.
According to the report, of the 23 million AstraZeneca shots administered worldwide, they expected 76 cases of GBS, but 190 events were observed, causing a 2.9-fold increased risk.
Although it cannot be proven that the vaccine caused these events, there is evidence that the vaccine triggers the immune system to attack its own nerves.
Meanwhile, the study also confirmed a threefold higher risk of a type of heart inflammation called myocarditis, although researchers did not report the number of expected cases versus actual cases.
Myocarditis was most commonly seen in young men. It is believed to be related to the immune response that triggered my mRNA vaccines from Pfizer and Moderna, which work by instructing cells to produce the same protein that sits on top of the coronavirus.
This prompts the immune system to produce antibodies against the spike protein, which provides protection against Covid. In rare cases, this immune response can lead to inflammation in the heart muscle.
Typically, cases of myocarditis have been relatively mild, which led to only 28 deaths.
In addition, both the first and fourth doses of the Moderna vaccine had a 1.7 to 2.6 times higher rate of pericarditis, an inflammation that affects the protective sac that covers the heart.
They looked at the more than 39 million Moderna vaccine doses administered.
Like the link between mycarditis and the vaccines, the link with pericarditis is still under investigation. It is thought to be caused by the same mechanism: an overactive immune response that attacks the thin sac-like membrane.
There was a greater than 3.7 times greater risk of a condition called acute disseminated encephalomyelitis (ADEM), which causes swelling in the brain and spinal cord that damages the protective covering of nerve fibers in the brain and spinal cord, after the first dose of Moderna. vaccine.
Seven cases of ADEM occurred after vaccination with the Pfizer-BioNTech vaccine, exceeding the expected number of two cases.
The study considered nearly 190 million shots.
The study also found that after receiving the first dose of the AstraZeneca vaccine, there was a 1.9 and 3.9 times increased risk of transverse myelitis and ADEM, respectively.
Bell’s palsy, which causes temporary weakness or paralysis of the muscles on one side of the face, had an increased risk of 1.05 after a first dose of the Pfizer vaccine.
There was also a 1.3 to 1.4 times greater risk of seizure after the first and second doses of the Moderna vaccine, as well as after the fourth dose of the Pfizer vaccine.
Researchers in Israel found 2.7 additional cases of myocarditis per 100,000 people injected with the Pfizer vaccine, but this shot up to 11 additional cases per 100,000 people who contracted the virus.
The graph shows the number of additional cases of each side effect per 100,000 people after a Pfizer shot (grey bars) and a Covid infection (orange bars)
The researchers added an important caveat to this finding: ‘The odds of a neurological event after acute SARS-CoV-2 infection were up to 617 times higher than after COVID vaccination, indicating that the benefits of vaccination substantially outweigh the risks.’
After a first dose of the AstraZeneca vaccine, there was a 3.2 times greater than expected risk of cerebral venous sinus thrombosis (CVST).
The risks after the first dose of the Pfizer vaccine and after the second dose were 1.49 and 1.25 times higher.
CVST is a rare but serious condition characterized by the formation of blood clots in the major ducts that drain blood from the brain and return it to the heart after the AstraZeneca vaccine.
A total of 21 events were expected, while 69 events were observed.
Even after the first dose of the AstraZeneca vaccine, there was a 1.07 times higher risk of thrombocytopenia, a condition characterized by a lower than normal number of platelets in the blood.
After a third dose of ChAdOx1, the risk increased remarkably to 1.95.
Their research was published in the journal Vaccine.