COVID passes, the headache stays

What is long COVID?

The World Health Organisation (WHO) defines long COVID as symptoms which:

– generally begin around three months after becoming sick with COVID

– continue for at least two months and

– cannot be explained by another diagnosis.

As imprecise as this definition may be, this is how varied the manifestation of the illness is. For this reason, it also presents a particular challenge for the usual medical examination procedures. Affected people generally do not present with all the symptoms which are considered ‘typical’ for long COVID. Moreover, the symptoms are not permanent. They vary in severity and can even return after a symptom-free period. Most affected people are significantly impacted both in everyday life and in their overall wellbeing.

An unclear set of symptoms

Headaches, tiredness, shortness of breath, sleeping problems, joint and muscle pain, as well as anxiety and depression are among the frequently mentioned symptoms. In addition, there can be reductions in the ability to concentrate (also known as “brain fog”). There are also descriptions of changes to the senses of taste and smell – a phenomenon which is already familiar from acute COVID-19.

In terms of the frequency of the illness, the data from the available studies varies significantly. Depending on the study, the proportion of patients who initially became infected with COVID-19 is between 7 and around 40 percent, including both mild and severe courses, as well as hospitalisation.

A comprehensive evaluation of more than 30 studies showed, for example, that two months after the acute illness, the proportion of long COVID patients was around 17 percent, after six months this became 8 percent. According to an American study from 2023, 7 percent of convalescent patients showed signs of long COVID. One in four of those affected complained of limitations in everyday life.

Headache as a companion to viral illnesses – and also afterwards for COVID-19

The fact that headaches are one of the most common symptoms both in the context of an acute COVID-19 illness and for long COVID has been proven by numerous studies. This is unsurprising, as other viral infections can also often be accompanied by headaches. However, with long COVID, there is the additional risk that these pains can become chronic, or permanent. This impacts the affected people for a long time, even after the original viral infection has worn off.

The connection between long COVID and headaches can occur in different ways. For example, some people with migraine find that their existing illness worsens. After becoming infected with COVID, attacks occur more frequently or last longer than before.

For people who did not suffer from headaches prior to becoming ill with COVID-19, headaches can develop for the first time after the original infection has subsided. It seems that people with pre-existing symptoms are more likely to experience long-term difficulties due to headaches than people with no prior history with headaches.

A long COVID headache can manifest in affected people either as symptoms similar to migraine or as symptoms which are more consistent with tension headache.

How does a long COVID headache develop?

The emergence of the long COVID headache has been the subject of research since its discovery. For a long time, it was unclear what was causing the symptoms. It was speculated that the virus led to overall organ damage, that the immune system was affected, that viruses were persisting in the body, or that the prescribed medications had caused unwanted side effects.

A recently published paper from the USA (October 2023) could signal a breakthrough in the search for a cause. The researchers discovered that, during the acute illness with COVID-19, patients experienced a drop in serotonin circulating in the blood. Serotonin is a messenger substance in the human body. Its effects are highly varied. It affects the cardiovascular system, blood pressure and clotting, the gastrointestinal system, as well as pain perception and processing, to name only the most important ones.

In convalescent patients, serotonin levels returned to normal after they had overcome the viral infection. However, if the affected people developed long COVID, serotonin levels remained low. A similar lack of serotonin was also found in patients who had become infected with other viruses. Potentially, these findings have uncovered a general response to viral infections in the human body.

Immune response, serotonin, and headaches – a sensitive connection

When we come into contact with a virus, our innate immune system releases an increased number of so-called type I interferons. These immune messenger substances affect the intestinal mucosa, in which serotonin is formed. The interferons hinder the creation of serotonin in cells in the intestinal mucosa. A low serotonin level affects the coagulation activity of certain blood cells, the thrombocytes. This leads increasingly to the formation of microscopic, little clots in the blood vessels, which are frequently found in patients with long COVID. These can affect the blood supply.

The lack of serotonin also affects the function of the brain. While it cannot overcome the so-called blood-brain barrier, it is suspected that there is another mode of influence: if there is not enough serotonin available, the function of the so-called vagus nerve is affected. Among other things, this nerve is actively involved in controlling processes affecting memory, information storage, and also headache occurrences. This would explain the long COVID symptoms which lead to the typical dysfunctions – ‘brain fog’ – i.e., difficulty concentrating and fatigue, as well as headaches.

Vaccines are the key – even against long COVID

The good news: it is now well-substantiated that the COVID-19 vaccine can not only protect you from severe cases of the actual illness, but also significantly lowers the risk of long COVID. This means: the vaccine can also prevent secondary symptoms. A so-called booster vaccine, i.e., refreshing the protection given by the vaccination, is particularly effective here. For example, a study on healthcare workers was able to show an inverse relationship between the number of COVID-19 vaccinations and the risk of becoming sick with long COVID. According to the study, the likelihood of long COVID was reduced by two thirds after three vaccinations. We can therefore assume that the most effective preventative measure, not only against becoming ill through an infection with the virus, but also against long COVID, is the consistent use of the vaccine.