Researchers from King's College London have identified five main factors that are associated with whether Covid-19 patients experience symptoms long term, according to a preprint study released Monday.

Recovery clinics for Covid-19 long-haulers

Study details

For the study, which has not yet been peer-reviewed, researchers analyzed data from the Covid Symptom Study app. The researchers focused their analysis on 4,182 of the app's users who had tested positive for the novel coronavirus using a polymerase chain reaction test and had been consistently logging their symptoms.

While most people with Covid-19 report no longer experiencing symptoms after about 11 days, the researchers found that:

• 13.3%, or 558, of the 4,182 app users reported having Covid-19 symptoms for at least four weeks;
• 4.5%, or 189, of the 4,182 app users reported having symptoms for eight weeks; and
• 2.3%, or 95, of the 4,182 app users reported having symptoms for more than 12 weeks.

The researchers noted, however, that those estimates were "conservative," and "because of the strict definitions used, [the figures] may underestimate the extent of" long-term Covid-19 symptoms among the sample of app users.

According to the researchers, the app users who experienced long-term Covid-19 symptoms commonly reported having heart symptoms such as palpitations or fast heartbeat, problems concentrating (or so-called "brain fog"), and numbness or pins and needles. Overall, the researchers said the commonly reported symptoms seemed to fell into two categories: one that mainly involved respiratory symptoms such as a cough and shortness of breath, fatigue, and headaches; and a second category with symptoms that were "clearly multi-system, affecting many parts of the body, including the brain, gut and heart." The researchers also found that people who reported having long-term Covid-19 symptoms were twice as likely to report that their symptoms had returned after they believed they had recovered from the disease when compared with people who had reported experiencing short-term symptoms.

In addition, the researchers identified five factors that were associated with people being more likely to experience long-term Covid-19 symptoms:

• Being older;
• Being overweight or having a slightly higher-than-average body mass index;
• Being female;
• Having asthma; and
• Having experienced a greater number of different Covid-19 symptoms during their first week of illness.

For example, the researchers found that females in the study were 50% more likely to experience long-term Covid-19 symptoms than males—with 14.5% of females developing long-term symptoms, compared with 9.5% of males. Further, the researchers found that 10% of adults between the ages of 18 and 49 with Covid-19 experienced long-term symptoms, while 22% of adults older than 70 with Covid-19 experienced from long-term symptoms.

The researchers then used the data from their analysis to design a statistical model to predict which patients are at most risk of experiencing long-term symptoms of Covid-19, and they tested the model against an independent data set of 2,472 people who reported having a range of Covid-19 symptoms and testing positive for antibodies to the novel coronavirus.

The researchers' statistical model was able to predict 69% of people who developed long-term Covid-19 symptoms, and it was 73% effective at avoiding false positives. When the researchers used their model to extrapolate their findings to the general population in the United Kingdom (U.K.), they estimated that:

• 14.5% of U.K. residents who experienced Covid-19 symptoms would be ill for at least four weeks;
• 5.1% of U.K. residents who experienced Covid-19 symptoms would be ill for at least eight weeks; and
• 2.2% of U.K. residents who experienced Covid-19 symptoms would be ill for at least 12 weeks.

Implications

King's College London in a release said the researchers' findings "could be used to help target early interventions and research aimed at preventing and treating" long-term Covid-19.

Claire Steves, one of the study's senior authors and a senior lecturer at King's, said, "It's important we use the knowledge we have gained from the first wave in the pandemic to reduce the long-term impact of the second. This should pave the way for trials of early interventions to reduce the long-term effects."

Tim Spector, a lead researcher on the study and a professor of genetic epidemiology at King's, said, "Covid-19 is a mild illness for many, but for one in 50 symptoms can persist for longer than 12 weeks. So it's important that, as well as worrying about excess deaths, we also need to consider those who will be affected by long Covid if we don't get the pandemic under control soon" (Ellyatt, CNBC, 10/21; King's College London release, 10/21).