For most people, infection with SARS-CoV-2 – the virus that causes COVID-19 – leads to mild short-term symptoms, acute respiratory illness or possibly no symptoms at all. But some people have long-lasting symptoms after infection – this has been dubbed the “long COVID”.
Scientists are still researching COVID for a long time. It is not well understood, although our knowledge about it is growing. Here, I take a look at what we’ve learned about it so far – who is at risk, how common it is and what its effects are.
By defining who is at risk for long COVID and the mechanisms involved, we can reveal appropriate treatments to try – or whether measures taken early in the course of the disease can alleviate it.
Broad vulnerability
Long COVID is characterized by a constellation of symptoms, including – variably – shortness of breath, severe fatigue, headache and loss of the ability to taste and smell normally.
A relatively large study of 384 individuals sick enough to be admitted to the hospital with COVID-19 showed that 53% remained out of breath in a follow-up assessment one to two months later, with 34% having a cough and 69% reporting fatigue.
In fact, the initial analysis of self-reported data sent through the COVID Symptom Study app suggests that 13 percent of people who have symptoms of COVID-19 have them for more than 28 days, while 4 percent have symptoms after more than 56 days.
Perhaps unsurprisingly, people with more severe illness initially – characterized by more than five symptoms – appear to be at increased risk for long COVID. Advanced age and female gender also appear to be risk factors for prolonged symptoms, as well as a higher body mass index.
Those who use the app tend to be the most capable of the population, with an interest in health issues. It is therefore surprising that such a high proportion has symptoms one to two months after the initial infection. These are generally not highly vulnerable to COVID-19.
Other initial research (awaiting peer review) suggests that SARS-CoV-2 may also have a long-term impact on people’s organs. But the profile of the people affected in this study is different from those who report symptoms through the app.
This survey, which looked at a sample of 200 patients who recovered from COVID-19, found moderate organ involvement in 32% of people’s hearts, 33% of the lungs and 12% of the kidneys. Multiple organ injuries were found in 25 percent of patients.
The patients in this study had an average age of 44 years, therefore, they were part of the young population of working age. Only 18 percent were hospitalized with COVID-19, which means that organ damage can occur even after a minor infection. Having a disease known to cause more serious COVID-19, such as type 2 diabetes and ischemic heart disease, was also not a prerequisite for organ damage.
Finding out what’s going on
There are many reasons why people may experience symptoms months after a viral illness during a pandemic. But getting to the bottom of what’s going on inside people will be easier for some parts of the body than for others.
When symptoms point to a specific organ, the investigation is relatively straightforward. Doctors can examine the electrical flow around the heart if someone is suffering from palpitations. Or they can study lung function – tissue elasticity and gas exchange – where shortness of breath is the predominant symptom.
To determine whether kidney function has deteriorated, the patient’s blood plasma components are compared to those in urine to measure how well the kidneys are filtering waste products.
A little more difficult to explore is the symptom of fatigue. Another recent large-scale study showed that this symptom is common after COVID-19 – occurring in more than half of the cases – and does not appear to be related to the severity of the initial disease.
Furthermore, tests showed that the people examined did not have high levels of inflammation, suggesting that their fatigue was not caused by continuous infection or by their immune system working overtime.
The risk factors for long-term symptoms in this study included being female – according to the COVID Symptom App study – and, interestingly, having a previous diagnosis of anxiety and depression.
Although men are at a higher risk of serious infection, the fact that women appear to be more affected by long COVID may reflect their difference or change in hormonal status. The ACE2 receptor that SARS-CoV-2 uses to infect the body is present not only on the surface of respiratory cells, but also in the cells of many hormone-producing organs, including the thyroid, adrenal gland and ovaries.
Some symptoms of long COVID overlap with menopausal symptoms, and hormone replacement with medications can be a way to reduce the impact of symptoms. However, clinical trials will be essential to determine precisely whether this approach is safe and effective. Requests to launch such surveys have been made.
With so much going on in the past year, we will need to separate which impacts stem from the virus itself and which may be the consequence of the huge social disruption caused by this pandemic.
What is clear, however, is that long-term symptoms after COVID-19 are common and that research into the causes and treatments of long COVID is likely to be needed long after the outbreak itself has subsided.
Frances Williams, Professor of Genomic Epidemiology and Honorable Rheumatologist, King’s College London.
This article was republished from The Conversation under a Creative Commons license. Read the original article.