Two very unusual side effects of COVID-19 vaccines named

Two very rare side effects of the Covid vaccine have been identified in a global study of 99 million people. The results confirm how rare the known complications are, and researchers say the benefits of the vaccines continue to “significantly outweigh the risks.”

Two new but exceptionally rare side effects of the Covid-19 vaccine – a neurological disorder and inflammation of the spinal cord – were discovered by researchers in the largest vaccine safety study to date.

According to The Guardian, the study, which included more than 99 million people from Australia, Argentina, Canada, Denmark, Finland, France, New Zealand and Scotland, also confirmed how rare known complications from vaccination are, and researchers confirmed that the benefits of vaccines against Covid-19 still “significantly outweigh the risks.”

Researchers working as part of the Global Vaccine Data Network used de-identified electronic health data to compare the incidence of 13 brain, blood and heart diseases in people after receiving the Pfizer, Moderna or AstraZeneca vaccine with the incidence that would be expected for these conditions in the population before the pandemic.

The study confirmed with a high degree of certainty the known link between the mRNA vaccines (Pfizer and Moderna) and the rare side effects of myocarditis (inflammation of the heart muscle) and pericarditis (swelling of the thin sac that covers the heart). The study also confirmed Guillain-Barré syndrome (in which the immune system attacks nerves) and cerebral venous sinus thrombosis (a type of blood clot in the brain) as rare side effects associated with the AstraZeneca vaccine.

But a new rare side effect, acute disseminated encephalomyelitis – inflammation and swelling of the brain and spinal cord – was also identified in the data analysis as being linked to the AstraZeneca vaccine.

The results were published in the international journal Vaccine on Friday.

Professor Jim Buttery, co-director of the Global Vaccine Data Network, said the discovery prompted researchers to independently confirm the side effect by completing a second study, this time analyzing a separate data set of 6.8 million Australians who received the AstraZeneca vaccine.

Not only did the Australian study confirm acute disseminated encephalomyelitis as a rare side effect, but a large amount of AstraZeneca-specific data also allowed them to discover a second new rare side effect known as transverse myelitis, or inflammation of the spinal cord.

The Australian study, also published Friday in the journal Vaccine, found that the findings suggested an extremely low risk of acute disseminated encephalomyelitis – 0.78 cases per million doses and 1.82 cases per million doses of transverse myelitis.

Professor Buttery, who is also a senior research analyst at the Murdoch Children’s Research Institute in Australia, said: “For rare side effects, we won’t know about them until the vaccine has been used in millions of people”: “No clinical trial will never be able to reach the scale to answer these questions, and so we will only know these questions after the vaccine is introduced.”

Buttery says the risk of myocarditis from natural Covid infection is even higher than after vaccination.

Both conditions are serious, but patients usually recover from them, he said.

Professor Julie Leask, a vaccine expert at the University of Sydney, said it was important to keep these findings in perspective and that Covid infection increases the risk of some of these rare conditions “far more than the vaccine”.

She said the research also confirmed that “our vaccine experts pay attention to when vaccines cause serious side effects, and they act accordingly. Having confidence in the system to identify problems and correct them is a very important part of a robust vaccination program.”