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 their infection – this is called “long COVID”.
Scientists are still researching COVID. It is not well understood, although our knowledge of it is growing. Here I take a look at what we’ve learned about it so far – who is at risk, how often does it occur and what are its effects.
In determining who is at risk from long-term COVID and the mechanisms involved, we can reveal which treatments are appropriate to try – or if steps taken early in the course of the disease can improve it.
Broad vulnerability
Long-term COVID is characterized by a range of symptoms, including – variably – shortness of breath, marked fatigue, headache and loss of normal taste and smell.
A relatively large study of 384 individuals sick enough to be hospitalized with COVID-19 found that 53 percent were breathless in a follow-up study one to two months later, with 34 percent coughing and 69 percent reporting fatigue.
Indeed, early analysis of self-reported data submitted through the COVID Symptom Study app suggests that 13 percent of people who experience COVID-19 symptoms have them for more than 28 days, while 4 percent have symptoms after more than 56 days.
Perhaps unsurprisingly, people with more serious illness – characterized by more than five symptoms – appear to be at an increased risk of long-term COVID at first. Older age and being female also seem to be risk factors for having long-lasting symptoms, as well as having a higher body mass index.
Those using the app tend to be on the fitter side of the population, with an interest in health issues. So it is surprising that such a large proportion show symptoms one to two months after the initial infection. In general, these are not people who are very vulnerable to COVID-19.
Another early study (pending peer review) suggests that SARS-CoV-2 can also have a long-lasting impact on people’s organs. But the profile of those affected in this study is different from those who report symptoms through the app.
This study, which looked at a sample of 200 patients who had recovered from COVID-19, found mild organ dysfunction in 32 percent of people’s hearts, 33 percent of people’s lungs, and 12 percent of people’s kidneys. Damage to multiple organs was found in 25 percent of the patients.
The patients in this study had an average age of 44 years and thus made up a large proportion of the young working-age population. Only 18 percent had been hospitalized with COVID-19, meaning organ damage can occur even after a non-serious infection. Having a disease known to lead to more severe COVID-19, such as type 2 diabetes and ischemic heart disease, was also not a prerequisite for organ damage.
Find out what’s going on
There are many reasons why people can have symptoms for months after a viral illness during a pandemic. But figuring out what’s going on in people will be easier for some parts of the body than others.
Where symptoms indicate a specific organ, research is relatively straightforward. Doctors can examine the electrical current around the heart if a person is experiencing palpitations. Or they can study lung function – tissue elasticity and gas exchange – where shortness of breath is the predominant symptom.
To determine if kidney function has deteriorated, components in a patient’s blood plasma are compared with those in the urine to measure how well the kidneys filter waste products.
The symptom of fatigue is more difficult to investigate. Another recent large-scale study has shown that this symptom is common after COVID-19 – which occurs in more than half the cases – and does not appear to be related to the severity of the early illness.
In addition, tests showed that the people studied did not have elevated levels of inflammation, suggesting that their fatigue was not caused by ongoing infection or by overtime of their immune systems.
Risk factors for long-term symptoms in this study included being a woman – in line with the COVID Symptom App study – and, interestingly, having a previous diagnosis of anxiety and depression.
Although men are at an increased risk of serious infection, women may seem more likely to suffer from long-term COVID, which may reflect their different or changing hormone 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 on the cells of many organs that produce hormones, including the thyroid, adrenal gland, and ovaries.
Some symptoms of long-term COVID overlap with menopausal symptoms, and hormone replacement with medication may be one way to lessen the impact of the symptoms. However, clinical trials are essential to accurately determine whether this approach is both safe and effective. Applications have been submitted to initiate such research.
Because so much has happened in the past year, we will have to find out what effects are the result of the virus itself and which could be the result of the massive social disruption caused by this pandemic.
What is clear, however, is that long-term symptoms after COVID-19 are common, and research into the causes and treatments of long-term COVID will likely be needed long after the outbreak itself resolves.
Frances Williams, Professor of Genomic Epidemiology and Hon Consultant Rheumatologist, King’s College London.
This article has been republished from The Conversation under a Creative Commons license. Read the original article.