For many people, the consequences of catching COVID-19 have been no worse than catching a common cold. For others, COVID-19 can see one or more symptoms persisting months after the infection has cleared their body. These people are said to be experiencing ‘long COVID’. Professor Stuart Berzins discusses the latest research surrounding long COVID, including its causes, symptoms and emerging treatments.
What is long COVID?
Long COVID is defined as having symptoms that persist at least two months after recovering from the initial COVID-19 infection. These people no longer test positive to COVID-19, but they continue to experience one or more symptoms that include fatigue, body aches, lack of energy (asthenia), breathlessness (dyspnea), cognitive difficulties (‘brain fog’), anxiety, loss/change of taste and/or smell (dysgeusia/anosmia) and heart palpitations — and there are others too. Fortunately, people with long COVID rarely experience more than a few, but the breadth of symptoms has made it difficult to know whether long COVID is one condition or many.
One concerning feature of long COVID is that it seems to persist for extended periods. One recent study showed that very few people with long COVID symptoms at five months had improved seven months later. This has raised concerns that long COVID could become an increasingly prevalent health issue unless we develop new approaches to identify and treat high-risk individuals.
Who is likely to develop long COVID?
Long COVID can affect anyone who has contracted COVID-19, including people who were initially asymptomatic. However, it appears that the severity of the initial infection and the viral load (amount of virus) is a factor. One study found that people hospitalised with COVID-19 had a higher incidence of long COVID, whereas vaccinated individuals (who have a reduced likelihood of serious illness) had a lower incidence. Women are more likely to develop long COVID than men, and obesity is also a significant risk factor.
There are conflicting accounts about the proportion of people who develop long COVID. Several studies report that 20-30 per cent of infections lead to some form of long COVID and one large study reported that less than a third of individuals felt fully recovered one year after their infection, although that study focused on people who had been hospitalised.
More reassuringly, a recent UK study compared the impact of COVID-19 to that of other respiratory illnesses (e.g. colds) and found that while more than 30 per cent of COVID-19 patients reported long-term symptoms, this was also experienced by about 20 per cent of patients after a non-COVID respiratory illness.
The differences between studies are likely due to the demographics of the study participants and how each study defined and measured symptoms, but many other factors could also be at play. A caveat to all of these studies is that they involved people who contracted earlier forms of the virus, such as Delta, whereas a far larger number of people are now being infected by Omicron variants. Whether different variants confer the same likelihood or symptoms of long COVID is not yet known. Clearly, there is still much to learn.
What causes long COVID?
There is growing evidence that ongoing inflammation is associated with long COVID, so a key challenge is determining why this is occurring and whether it is causing the condition. Some researchers believe that inflammation is occurring because the immune system is being over-stimulated by residual virus in some parts of the body or that the immune response is not regulated effectively and hasn’t’ ‘turned off’ properly once the virus has been cleared. Others suggest that the immune response against the COVID-19 virus can trigger a chronic autoimmune response that can cause neurological damage that leads to a diverse range of symptoms.
Interestingly, long COVID has some similarities with chronic fatigue syndrome, which is also poorly understood and often triggered by a viral infection.
What is being done to treat long COVID?
Many researchers are attempting to develop treatments for long COVID, but the myriad symptoms and uncertainty about their causes are hampering progress. Treatments for individual symptoms are starting to emerge, including ‘re-training’ of taste and smell senses and carefully managed rehabilitation programs to treat fatigue. It is now clear that fatigue and exhaustion associated with long COVID should be managed very carefully, as ignoring them or ‘pushing through’ is associated with short- and long-term worsening of the symptoms.
How can you avoid long COVID?
The best defence is to avoid contracting COVID-19, so take sensible precautions against infection and ensure vaccinations are up to date. If you do catch COVID-19 and experience symptoms for longer than expected, it is advisable to consult a doctor, even if the symptoms seem relatively minor. Most people will recover quickly from COVID-19 without ongoing symptoms, but long COVID is a new condition that we don’t fully understand, so it makes sense to treat it with caution.
The high rates of vaccination have seen COVID-19 becoming a mild illness for most people who contract it. This has meant the harsh restrictions required earlier in the pandemic are now relaxed or removed entirely, but variants such as Omicron are so transmissible that community infection rates remain extraordinarily high. For some people, long COVID will be a consequence of their infection, so it is important that we remain vigilant about minimising COVID-19 cases and continue research in this area so that long COVID can be prevented or treated effectively.
Stuart Berzins is Professor of Immunology at Federation University. His group studies the role of specialised immune cells in diseases, including cancer and COVID-19.