Among the different facets of the SARS-CoV-2 virus that are still covered with uncertainty, the long-term sequelae that appear after infection stand out. Multiple scientists from different parts of the world are closely monitoring patients to find out how they evolve over time and how the effects of the disease could be prevented or treated. The United States has bet heavily on the investigation of this matter. Last December, the US Congress allocated more than one billion dollars to the National Institutes of Health (NIH) to fund projects for four years that study the long-term health consequences caused by the SARS-CoV-2 infection.
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The NIH estimated that between 10 and 30% of people infected with the coronavirus could suffer long-term symptoms. In Spain, according to the survey carried out by the Spanish Society of General and Family Physicians, 87% of those affected by persistent COVID-19 are women, with an average age of 43 years.
Persistent COVID-19, which in medical terminology is called by the English acronym feed (Post-acute sequelae from SARS-CoV-2 infection) encompasses a wide variety of symptoms and signs that can appear after coronavirus infection and persist for weeks or months. At the end of January, the preliminary results of a large study appeared (the results of which have not yet undergone peer review or been published in a scientific journal) that analyzed more than 18,000 publications and 47,000 patients to gather the accumulated joint knowledge on the PASC. The researchers found that around 80% of those affected by COVID-19 suffered one or more symptoms weeks or months after infection and identified more than 50 different symptoms / signs that could appear and remain over time.
The symptom that appeared most frequently was fatigue (58% of the people analyzed), followed by headache (44%), attention disorder (27%), hair loss (25%), difficulty breathing (24%), loss of taste (23%) and smell (21%), accelerated and deeper breathing (21%), and coughing (19%). For now, the causes behind this wide variety of sequelae are unknown and very different hypotheses are being considered: an inadequate reaction of the immune system that remains after the infection is resolved, post-traumatic stress, persistence of viral particles in some parts of the body …
Improvement, chance or causality?
With the mass vaccinations that are taking place in multiple countries, another more unknown facet about PASC is added: more and more people report that their symptoms have disappeared or have been alleviated shortly after receiving the vaccine. International surveys and different media such as The Washington Post, The Huffington Post, The country O Vozpópuli collect multiple cases of people explaining their evolution after the vaccine. Especially striking is the case of Arianna Einsenberg, 34, who experienced fatigue, insomnia, muscle pain and brain fog for 8 months after passing COVID-19. However, her symptoms disappeared within 36 hours after receiving the second dose of the SARS-CoV-2 vaccine. Are cases like Eisenberg’s just a fluke, or are vaccines really able to alleviate or eliminate persistent COVID-19 systems?
A first detail that must be taken into account when analyzing these cases is that correlation does not imply causality. Millions of people in the world are receiving vaccines against COVID-19 and it is possible that, by simple chance, the symptoms of persistent COVID disappeared coinciding with the time of vaccination, without the vaccine having anything to do with it. In addition, we must also take into account all those people who were vaccinated and continue to show the same symptoms as before receiving said preventive treatment.
Unfortunately, it is not possible to distinguish spontaneous recoveries from persistent COVID-19 from those triggered by vaccines simply through surveys, because we do not have a control group (people with persistent COVID-19 who have not received the vaccine) to compare. Precisely for this reason, clinical studies are necessary to confirm that, indeed, vaccines can be useful to treat PASC. For now, the investigations in this regard have important limitations as to draw conclusions, although they point in this direction.
In the hypothetical case that vaccines, indeed, were of benefit to people suffering from PASC, what would be the reason for this phenomenon? Since the causes behind persistent COVID-19 are not even known, any hypothesis about it falls within the realm of pure speculation. In any case, never underestimate the placebo effect. We know from many studies that certain people with symptoms such as pain, fatigue or insomnia can respond very well to placebos, substances that have no therapeutic effect, but that cause a benefit in the individuals who receive it.
Beyond the previous mechanism, it could be that the immune response enhanced by vaccines resulted in a hypothetical inappropriate reaction of the immune system, which attacked tissues or cells of the human body itself, to be resolved. Another possibility is that the vaccine managed to get the defense system to eliminate the hypothetical viral particles that could still be present in the body. For now, there are many questions in this regard, although the first question that will have to be resolved and confirmed is whether vaccines, indeed, offer benefits over persistent COVID.