Covid-19 Outcome

Getting over Covid-19: What are the data?

Patients admitted to hospital, especially those seriously ill enough to be admitted to an intensive care unit, not surprisingly frequently continue with ill health and take several months to recover back to their pre-Covid-19 fitness.  But what about the possible long term health problems following the much more frequent but less serious infections.  In this post I examine the data to answer this question.

What long term complications have been described following Covid-19 infection?

  • Although fortunately rarely, some hospitalised patients continue to be at risk of  serious heart, brain, lung, blood clotting and other complications of Covid-19  
  • Some of these problems are direct complications from the virus itself
  • Others come from an over-reaction by the body’s immune system: the so-called cytokine storm
  • Others result from being on a ventilator for many weeks
  • Further, anyone in a hospital bed for weeks loses muscle and their fitness plummets
  • All of these can obviously take some months to achieve full recovery

How large is the proportion of non-hospitalised (community) patients? .

  • This is a pyramid of the best estimates of the numbers with different grades of Covid-19 in the entire UK population, from March to September
  • Similar data apply to the other badly affected Western countries.
    • About 5% of the population have had the virus
    • Of those about half were ill
    • Of those about 1 in 10 were admitted to hospital (data correct to end September)
  •  Obviously in the elderly the picture is different.  However, the prevalence with infection is still around 5% and the overwhelming majority of cases are not admitted to hospital
  • What happens to the 1 in 40 (approximately 1.5 million people in the UK) who had symptoms of Covid-19 but were not ill enough to be admitted to hospital?

“Long-CoVid” in community cases 

  • Widespread surveys published  in the scientific journals and presented in all forms of media have emphasised the persistence of symptoms and ill health in many otherwise recovered Covid-19 patients
  • (The quality of the reports in the scientific press is not that much greater than in the lay media!) 
  • These reports have led to the prolonged ill health following infection being referred to as “long CoVid”
  • To bring about a consistency in labelling, the following definitions have been proposed:
  • There is not a single pattern as to what symptoms are still present at these time points
    • Some just have a persistent single symptom such as cough or loss of sense of taste and smell
    • Others have non-specific symptoms such as fatigue
    • Others have as many as 15 separate symptoms

An epidemiologist’s perspective: what do I want to know?

As an epidemiologist, I acknowledge that some people do have long term problems but I want to know

  • What is the actual proportion of those who had  Covid-19 who:
    • have continuing health problems?
    • have specific complications?
  • What is the time course in terms of:
    • how long to full recovery?
    • if there are new complications, over what time period do they occur?
  • Are there factors that will predict who is going to have problems?

There are also some very specific challenges to answering these questions!

  • Anyone in the general population can have health problems similar to the symptoms discussed above.  Hence the key question: Is the rate of symptoms higher, and if so by how much, than in the general population (in that age group)?
  • Left are listed complications from ‘normal’ flu*
  • An extension of that argument is that recovery from other  common  viral illnesses,  especially influenza, can be marked by persistence of symptoms and development of complications


  • It is not therefore a given that the persistence of problems following Covid-19  is more likely than that following other viral illnesses. However
    • The extent of the anecdotal  reports should not be ignored 
    • There are some seemingly very specific issues such as “Covid-19 toe” (see below) 
  • A second major challenge is knowing how representative are the patients who are being studied and whether there are any potential sources of bias in the data collection
    • Using  social media, a widely used  approach to recruitment, is unlikely to lead to a sample which is representative of the total population affected by Covid-19.
    • Further those who respond to such surveys are more likely to take part if they have symptoms

What do we know about the persistence of Covid-19 symptoms?
  • The best data, allowing for recruitment bias, comes from the King’s College London symptom app (my ex PhD student Tim Spector again!)
    • The graph above shows the proportion at different time points after onset who are still poorly; and the very slow in improvement to complete health.
    • From the graph, just under 10% are  still poorly after 1 month (30 days)
  • In a telephone survey in the USA of 292 people who had tested positive 25% were still not back to their pre-Covid-19 health by 3 months
  • In another social media based study there was a steady fall in the proportion still feeling unwell after 4 months 

What symptoms persist?

  • A recent Dutch study, recruiting 2159 patients, mean age 47, from Facebook identified a large number of symptoms that were still present at an average of 11 weeks after the start of the infection
  • Interestingly in that group there were no symptoms that were more common on follow up
  • The prevalence of all the symptoms surveyed  (there were over 30 in that survey) reduced  during the 3 months but the most common ones were slower to disappear
  • As indicated above many of the symptoms like cough, fatigue, breathlessness are seen after influenza

What do we know about risk factors for persistence?

It is still early days in terms of having robust data on these questions but there is a consensus that any or all of the following might be important in predicting who will have continuing problems:

  • Poor antibody response to fight the infection (perhaps due to age or general immune problem)
  • The opposite of the above ie a greater immune response with the virus leading to an increased level of inflammation (a high temperature is part of the body’s inflammatory response to a virus)
  • Relapse or reinfection (at the moment the latter is thought to be very rare)
  • Losing cardiovascular and muscular fitness from prolonged inactivity 
  • Mental health factors in recovering from an infection – some have likened this to a post-traumatic stress syndrome.  In some patients the symptoms are similar 


  • As far as is known, and maybe studies will change that conclusion, people who have tested positive but who had no symptoms whilst infected do not then develop problems later 
  • On the one hand there is a high level of persistent problems in people who have been ill, but on the other there is no unique pattern of symptoms to such continuing problems
  • It seems that the rates of symptoms, 3 months after Covid-19, are greater than following a bad attack of flu, but how much greater we don’t know.
  • The positive news is that over time most people will recover completely
  • The more problematic issue is given we don’t know any specific cause for the persistence of symptoms, then there is no Covid-19  specific treatment.  Each problem will have to be managed symptomatically  

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