Long-COVID risk factors uncovered

As coronavirus infections surge again - we think somewhere between 1 and 2 million cases are occurring around the country every week at the moment - conversations are frequently turning again to the question of “long covid”. It was quite soon after the pandemic began that significant numbers of people began to report symptoms that seemed to persist long after their coronavirus infection had gone away. This is where the name “long covid” came from. So how many people have been affected, and for how long? And who is most at risk? Ellen Thompson, at Kings College London, has found the main risk factors and she suggests that the number might sit somewhere around 17%, but if you drill down a bit further to pull out those cases for whom long covid has a major impact on their quality of life, it’s still about 5% of people...

Ellen - This paper aimed to look at the frequency of long COVID within the population and the risk factors. So we looked across a number of health and demographic risk factors for long COVID based on data that was collected between 2020 and 2021. So it doesn't incorporate the new variant of COVID-19 called omicron, but we do now have new data so researchers are starting to look at the impact of the different variants on things like long COVID.

Chris - And to be included in your study, what did a person have to do? Did they just have to test positive for COVID? How was it that you gathered the individuals you looked at?

Ellen - The data sets used were population already established data sets. So what we have in the UK is we have a number of longitudinal studies that track people over time. So we use data from those studies and we also use data from anonymized, electronic health records.

Chris - And what actually emerged when you look at the rates of people getting some kind of postviral syndrome, how many get it?

Ellen - Around 17% of individuals experience long COVID for more than 12 weeks. But I think what's important to say is that within our data, we looked at functionally debilitating symptoms, those that impact everyday life, we only found that around 5% of people experience those symptoms.

Chris - Do people actually really agree what symptoms constitute long COVID? Are we really comparing apples with apples? Because when you talk to some people, they'll say one thing and others will say another, but they're all being united under this umbrella "long COVID". So do we really, as a scientific community, have some kind of consistent definition?

Ellen - Currently the definition of long COVID does include a whole range of symptoms that people can experience, but within that, the most common types of symptoms are fatigue, loss of sense of smell, loss of sense of taste, as well as a cough and sometimes confusion or memory loss within that. So although there's a whole host of symptoms that people can experience, they're the most common type that have been seen within the data.

Chris - Did you though consider the general population who didn't have COVID at the same time because the office for national statistics have at certain points, published numbers suggesting that when they looked at people who had long COVID symptoms and no diagnosis of COVID, the numbers were a bit similar suggesting that perhaps what we're calling long COVID reflects real life for some people.

Ellen - Yeah, great question. So within our study, we were focusing on people who had COVID. So in order to be included in the analysis, we only based it on those who had COVID as a precursor of long COVID. However, we did use some statistical techniques in order to account for the probability of getting COVID. So we feel relatively confident within a certain degree of certainty that we're sort of showing that long COVID is an outcome for people that do have COVID and there are certain risk factors for getting long COVID.

Chris - And what are they?

Ellen - Female sex, increased age, overweight and obesity and underlying health problems or pre-existing health problems were predictors of long COVID within our data.

Chris - And did you look longer term beyond the 4 weeks or some people using three months as a definition of long COVID aren't they, but if we go out longer, is there sort of good news for people who might find themselves in this position, things are going to get better?

Ellen - We did look at by 4 weeks and 12 weeks, we don't have the data yet to look longer. Well, I should say we do now and that's exactly what we're doing. So we're currently planning a study on looking at recovery of long COVID as well as longer term symptoms.

Chris - But does it look like people can look forward to feeling better in the future? Or are there people condemned to stay long COVID positive indefinitely?

Ellen - Yeah, we hope so. There is evidence coming out that suggests that symptoms do subside after a certain amount of time in most cases. I think what will be important is to think about why and for whom symptoms are continuing for longer, as well as think about predictors of recovery. So what's really helping people recover from COVID.

Chris - And to what extent is this exclusive to coronavirus infection? And to what extent do you see the same sort of manifestation in the aftermath of a bad flu?

Ellen - Yeah, that's a good point. So when we're talking about long COVID, we are specifically talking about outcome of COVID-19, but we do know that post-viral fatigue, for example, does exist with other infections. However, we think it's important to think about long COVID of how common COVID-19 is and the fact that we are still in the midst of a global pandemic.