Debilitating symptoms from COVID-19 can last well past the initial course of the disease for some patients. Researchers have been trying to figure out what triggers cases of long COVID and if certain people are more susceptible to it.

Dr. David Strain heads the British Medical Association's work on the long-term impact of COVID-19. He has also had the disease himself. He recently spoke with DW.

Deutsche Welle: Is there any way of speeding up recovery for sufferers of long-term COVID? 

Dr. David Strain: That's a really interesting question because we don't really know what the natural history of COVID itself is. So, I get many reports of people who, for example, are taking multi-vitamins or are taking other health supplements and swear that it has made a dramatic difference for them. 

But I also get reports from people who've done no intervention and have got dramatically better for no apparent reason. Whereas in all cases, we get people who don't get better.  

At this moment in time, in the absence of randomized control trials, we don't have any definitive answer as to what will or won't work. 

Take us back to the beginning. What causes long COVID in the first place? 

That, in itself, is a huge question. That may help us to identify what the treatments are, but at the moment we don't fully understand. There are two or three different hypotheses that are being run.  

The first and the one that I'm researching is looking at the mitochondria – that is the powerhouse of the cells. Effectively, if you want to think of them as the battery that powers your body. Basically, we know COVID-19 does attack that battery.

And what we believe is happening is that there are many individuals for who that battery just isn't recharging after the disease. It's like having the old iPhone. It doesn't matter how long you plug it in for, it will not get the charge that it requires. And we think that's what's going on and that's the theory we're working on.  

There are others that think that this is an autoimmune disease, the antibodies you create to the virus, then turn on the host and effectively become like rheumatoid arthritis or SLE [Systemic lupus erythematosus] and trigger an autoimmune disease. There are some that think there is permanent scarring that takes place in the lung and the blood vessels that occur as a result of the virus.

The bottom line is, at the moment we don't know. And the reality is, it's likely to be a combination of multiple different causes. 

What about just how many people this actually affects? What do you make of the Chinese study that shows two thirds of hard-hit patients suffer long term effects? 

When you're looking at the hard-hit, it's no surprise at all. If you look at people who've been on ITU [intensive treatment unit] for other reasons, many of those will still have long-term effects, six or even 12 months later. I think what's more interesting in long COVID is a number of people that only got relatively mild disease.

I mean, for me personally, I only had one day that I needed any additional therapy. Yet I've been left with symptoms 12 weeks later that are actually worse than the initial disease. And these are the ones that are causing more issues.  

From the ONS – the Office of National Statistics in the UK – they estimate that 20% of people who had any symptoms at all are left with some debilitating illness at six weeks and 10% of people, even though they didn't require hospitalization or any additional care at the outset, 10% of people who ever tested positive will have symptoms of long COVID at three months. 

And you've said this is happening to younger people, more women than men, those suggested to be at lower risk? 

Exactly, and that's part of the thing that we're seeing – particularly in the health care setting – that the risk of dying from COVID is much lower in females, it's much lower in the youngsters, and therefore in many health care settings, these are the people that we get to work the frontline because if they catch COVID, the consequences won't be as severe. But now what we're seeing as an aftereffect is that these are exactly the people that are more at risk of long COVID.  

In our study, we've identified that even though women are more likely to self-present and self-participate in study, even after we adjust for that, 86% of the long COVID that we're seeing is in younger, fitter ladies. And it does appear to be very similar that all of the people who are presenting with symptoms of long COVID were previously very fit, they were very active.  

We're not sure if that represents that they have a higher baseline and therefore they realize it a lot more if they've been left with some weakness. It may just be that these are the people that are actually noticing it, because while most of us around the world are in some form of lockdown where we don't have the same freedoms that we have normally, that we just don't notice how much this has had an impact on us. 

You've also said this isn't just a respiratory infection, it's a multisystem disease. Are there steps that can be taken to prevent long COVID from setting in? 

We don't really know what the cause is, so it's very difficult to say for certain. But one thing that we are trialing and having good response with is making sure that when you've got the illness, you stay within your exercise envelope or your energy envelope, we call it.  

For many other people, if you're training for a marathon or if you're training for a race, you want to push yourself every single time you train. With long COVID, what we believe is if you stay well within your energy window, then the window itself will get bigger over time rather than us trying to push. Because one of the key things that all of us are seeing is the harder you push yourself, the longer it takes to recover after each episode. So, stay within your energy envelope at every available opportunity. 

Dr. David Strain is a senior clinical lecturer at the College of Medicine and Health at the University of Exeter in the UK.

This interview was conducted for TV and has been edited for clarity.