What is myelitis, the disease that has stopped Oxford’s COVID-19 vaccine?

Yesterday there was news in the media that a woman who had been injected with the COVID-19 vaccine suffered transverse myelitis, an inflammation of the spinal cord. This has led to the clinical trial on the vaccine being temporarily suspended. Dr. Mar Tintoré, specialist in Neurology at Hospital Quironsalud Barcelona and member of Top Doctors, answers some questions about the disease and the relationship with the vaccine.

What exactly is myelitis and transverse myelitis?

The word myelitis means that there is inflammation at the level of the spinal cord. This inflammation translates clinically with a tingling sensation that can go up from the feet to the hips and higher, depending on where the inflammation is located.

The patient usually notices a loss of sensibility in the legs, associated with a loss of strength, sometimes in both legs or in one of them. If the inflammation is in the upper part of the medulla, in addition to losing strength and sensitivity in the legs, it may also affect the hands. Normally, strength and sensitivity are lost, and the sphincters are also frequently affected. This means that the patient can produce a retention of urine, stop being able to urinate and even defecate.

As always happens in medicine with all diseases, there are myelitis that are of little impact and slightly affect the patient, with symptoms only in the legs in the form of tingling but without loss of sensitivity or sphincter involvement. On the other hand, there are cases that are more serious, where the patient could completely lose the strength and sensitivity of both legs and arms.

Myelitis is an inflammation, so it usually goes up for a few days or even weeks, it can stabilize and then, depending on the damage that has occurred, there is often a recovery that can be partial or complete, based on many factors (age, severity of the myelitis or the causes that triggered it).

The patient who developed myelitis as a result of the COVID-19 vaccine has been discharged, which does not mean that she has been cured but perhaps that her symptoms have ceased. However, the details of when the myelitis started and how long it may have lasted are also unknown.

Why does myelitis usually develop?

An inflammation in the spinal cord or myelitis can be caused by different reasons. A myelitis may be in the context of other pathologies or problems, such as multiple sclerosis or other autoimmune diseases. In other cases myelitis is a single problem and inflammation in the spinal cord occurs as a result of a virus. There are also other cases of vaccine-associated myelitis, although sometimes the relationship between vaccines and myelitis can be controversial.

What may have happened with the Oxford vaccine to cause a patient to develop transverse myelitis?

When a vaccine is injected, and in this case the vaccine being developed by AstraZeneca, the process is as follows: an adenovirus (a virus that causes, for example, constipation) is collected, genetically modified and a protein containing COVID is added. In this way, the patient’s defenses are expected to develop a response against this COVID fragment, which would be sufficient to develop a protective response and not cause the disease. Researchers include only a very small percentage of COVID so that the body develops protection against COVID without suffering the disease, which is actually what all vaccines do.

When a new element, or a fragment of virus, is added, it sometimes happens that, by mechanisms called molecular mimicry (which can occur with viruses and with vaccines, although it is controversial), there are parts of viruses that look like pieces of myelin. It is then when our defenses attack, for example, the virus (which is what they should do), and they find pieces of virus similar to other pieces of myelin, and that is when they begin to attack the medulla by an erroneous mechanism. In a way the immune system is being stimulated for a purpose but sometimes it can get it wrong and attack the marrow. This is what we would call an autoimmune cross-reaction because there are molecules that are similar. What is sought is to stimulate the immune system to generate a protective response against COVID and this stimulus could, at a given moment, develop a response against the marrow, producing this inflammation.

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However, it has only occurred in one patient out of thousands, so the causality is not very clear, but it is enough to decide to momentarily stop vaccination and continue researching. And that is precisely what should not be surprising. In all clinical trials, in which a great many people are involved, it can happen that a person suddenly develops some pathology that could be related to the immune system, so the fact that a pause is made to analyze means that the scientific regulatory mechanisms are working, and that there is a committee of experts outside the laboratory that is reviewing the research. This is something that should be seen as positive so that, after exhaustive analysis by the experts, the event will be considered to be related or not to the vaccine. In any case, it will mean that the safety elements that are being followed are working and that, in parallel to the pressures that they must be receiving to bring out the vaccine against COVID-19 as soon as possible, the regulatory mechanisms of science are working.

What is the process in Europe until a vaccine is approved for application? What is the time frame for demonstrating that it is safe?

In any vaccine development process there are timings and phases:

  • In phase 1, tests are carried out at the laboratory or animal level.
  • In phase 2, which is the one that has already been applied in this case, it is applied in a small number of patients who develop a protective response, with no adverse effects.
  • In phase 3, which is what is being carried out now, 30,000 patients are included. It is at this point that possible adverse effects can begin to be analyzed, which are usually very rare but, in order to find them, many people must be included.

Until any research reaches phase 3, certain aspects cannot be analyzed. It is at this point that a large number of patients are vaccinated and tested to see if they develop antibodies to COVID and that the safety is correct. No vaccine should be brought to market in Phase 2 because it has not been sufficiently tested and monitored in patients. It is at this point that errors can be detected and why an error may have occurred can be analyzed, vaccination stopped and further research carried out. It should also be analyzed whether the patient might have an underlying cause for developing myelitis. This case means that things are being done well and it is how science works, without pressure and without skipping oversight procedures, with independent mechanisms that monitor that everything works and is complied with.