Why the answer is more complicated than you think
Of the many lingering problems of the pandemic, one of the most difficult is Long Covid. Although it is a serious condition that afflicts many people who have recovered from their first Covid-19 infections, especially those who suffer from long-term debilitating symptoms, Long Covid often goes unnoticed. it is difficult to diagnose and even more difficult to treat. There are endless horror stories on the internet about previously healthy people being affected, sometimes after relatively mild initial infections with Covid-19, with persistent worsening of symptoms.
In other words, Long Covid is a serious problem and something we need to deal with as a society as a result of the pandemic.
Recently there has been a very heated debate about an important point - how many people can we expect to get Long Covid after the first infections? The headlines are filled with scary statistics that mean that almost everyone will eventually get the condition, that over 1/3 of those who suffer from Covid-19 are still suffering, and that we are all basically destined to get sick words. .
However, the truth is more complicated. A lot depends on definitions and when you look at the data the proportion of people with Long Covid is a complex subject and may be much lower than you have heard. Of course, a small fraction of a very large number still suffer from many people, but the true percentage may be lower than the most terrifying headlines suggest.
Let's look at the evidence.
Meaning
Definitions are important in epidemiology. A broad definition of the disease will often include more people, but may also reduce the usefulness of the term. Narrow may be more clinically useful, but it excludes people who may suffer from a milder version of the same disease.
Take the ongoing debate about what hypertension (high blood pressure) is. On the one hand, the lower the bar, the more people will have severe heart disease and benefit from treatment now. On the contrary, it also includes a large group of people who may not benefit from medication and can do without a diagnosis.
For a new and poorly understood disease, choosing the right definition ranges from important to critical. We will use the World Health Organization (WHO) clinical case definition, developed after a long process of consultation with patients, carers and health professionals, which states:
The post-COVID-19 condition occurs in people with a history of probable or confirmed SARS CoV-2 infection, usually 3 months after the onset of symptoms of COVID-19 and lasts for at least 2 months and cannot be explained by an alternative diagnosis. Common symptoms are fatigue, shortness of breath, cognitive impairment, etc. and often affect daily activities. Symptoms may appear newly after initial recovery from an acute episode of COVID-19 or may persist after a previous illness. Symptoms may also fluctuate or recur over time.
It's pretty broad, but when we look at the scariest, very high estimates, almost all of them use definitions that are much broader than this. For example, a recent CDC study titled "Nearly one in five US adults with Covid-19 has 'High rate of COVID'". If you look at the technical notes, it includes people who say they have Covid-19 and any new symptoms lasting 3 months or more.
It's easy to see why this might yield a high number. If you ask people if they have had different symptoms at any time since they had Covid-19 (which can be over a year ago), it is not surprising that many people will say yes. Fatigue, for example, is one of the most commonly reported symptoms of Long Covid, but it is also common in people who have not been exposed to Covid-19.
Another problem is the study population. This systematic review and meta-analysis estimated the global prevalence of any Long COVID at 44% after recovery from the first infection, but included most studies of hospitals or specific populations such as those over 65 years of age. When we look at estimates based on representative samples of the entire population, the prevalence drops dramatically, with one study finding that only 3.4% of people had symptoms for more than 4 months.
You can also determine this problem by thinking about the severity of the disease. According to the WHO and CDC definitions, Long Covid is any symptom of any severity – it tends to include anything from a mild on/off headache lasting several months to a severe illness that is not derived. However, if you focus on symptoms that cause severe effects on daily life – which can be clinically useful – this proportion should decrease.
You can see it in the data – a recent Office for National Statistics report from the UK found that 3% of the entire population experienced some form of long-term symptoms of Covid-19. In this population, about 72% of people reported that these symptoms affected their lives in the long term, and 20% reported that the symptoms significantly limited their daily activities. In other words, the bottom line is that 2 million people have Long Covid, but only one-fifth of those people have severe, debilitating disease.
Now it's important to note that a fifth of 3% of the entire population is still a very large number in absolute terms - in the UK it's over 400k people. Whichever measure you choose, Long Covid is still a huge problem affecting the world.
But it gets more complicated from here. How do we know that all these symptoms are directly caused by Covid-19?
Control groups?
This brings us to a moot point in the long debate about Covid – should we be comparing people to a control group without Covid-19 to see if the symptoms people are reporting are likely to be caused by the virus itself? The idea is that we shouldn't say that Covid-19 is the cause of all the Long Covid symptoms that we're seeing, because there's some underlying level that people will experience regardless.
Take this recent study – among people who were not hospitalized with Covid-19 in their data, the authors found that 5.4% of people had long-term symptoms months after their initial Covid-19 diagnosis. However, in the group of control patients not diagnosed with Covid-19, the rate of persistent symptoms was 4.4%. While there is some debate about the limitations of this paper - you can check out my Twitter thread and the ongoing debate if you're interested - the bottom line is that a proportion of people reporting symptoms are reporting them even if they don't exist. they have Covid-19.
You can also apply this type of analysis to other Long Covid estimates. One of the most cited articles in the Long Covid literature estimates that 34% of people who contract Covid-19 have ongoing neurological or psychological problems, a number that has grabbed headlines and scientific research. However, if you compare this to the study's control group, it's 5-8% more than the expected baseline who developed such symptoms, which may mean that only 5% of the observed symptoms were even caused by COVID-19.
Of course, it gets complicated when we start to consider what the control groups are. If we compare a control group with people who have recovered from other viral illnesses, such as the flu, does this mean that more viruses are causing the long-term symptoms? If people with fractures have higher rates of chronic nerve disorders than people with Covid-19, it probably doesn't mean that Covid-19 protects against nerve disorders, but could it mean that it has nothing to do with Long Covid? That is very hard to say.
These problems can be remedied to some extent by general population control – that is, by comparing everyone in society – but this has its own problems. Many people not yet diagnosed with Covid-19 have the infection, after all, something we know from human antibody studies.
All of this brings us back to the central point about definitions - technically, if we follow the WHO definition above and exclude people whose symptoms can be explained by causes other than Covid-19 with a control group, the rate of each Lange Covid after infection drops significantly from 20-30% to around 1-10%, depending on the study and population.
And that's before we discuss the difficulties of residual confounding, indicator confounding, and other epidemiological biases in studies trying to determine a causal relationship between Covid-19 infection and Long Covid symptoms. It is very difficult to know what proportion of people who report persistent symptoms after being infected with Covid-19 have symptoms caused by the infection itself. That doesn't mean the symptoms aren't "real" - people are clearly suffering - but it does mean we can't blame Covid-19 infections for all the ongoing illnesses we see.
Declining share?
Another interesting thing to note about Long Covid is that in study after study it is closely related to the severity of the disease. What I mean by this is that the rate of people experiencing long-term symptoms after recovering from Covid-19 is much lower in patients with a mild initial infection and rises to a much higher level in patients with severe pain.
The reason this is interesting is because we know from a lot of research that the proportion of people who get serious infections from Covid-19 drops suddenly. Estimates vary, but a combination of vaccination and immunity from previous infections has greatly reduced the number of people who get Covid-19.
Taken together – Long Covid correlates with disease severity and disease severity declines over time – these facts strongly suggest that fewer people will get Long Covid infection today than in 2020 and will likely continue to decline in the future.
In fact, there is even some evidence that this is the case - we know that vaccination reduces the rate of Long Covid, which can play a large part, and we expect that previous infection will provide the same protection. We can even see it in the population statistics - despite a huge increase in the number of people infected in 2022, the proportion of those with long-term symptoms in the UK has barely changed since January and may fall over time.
Overall, this means that your risk of Long Covid now is likely to be lower than your risk if you were infected in 2020, and your risk of infection in 2024 is likely to be even lower.
Bottom Line
It's important to note that nothing in this article—or anywhere in the evidence itself—suggests that people don't have symptoms. No one lies about being sick, and whatever definition we use, the fact remains that people are suffering and that's a big problem.
However, it is important to be clear about what the use of different definitions for Long Covid means in practice. If we decide that Long Covid should be described using the CDC definition, then many people with Covid-19 will meet the criteria. That being said, many people have mild concerns that resolve quickly that may not be caused by Covid-19.
If we instead use the WHO definition and include a control group in our assessment, we end up with a much smaller proportion of people with Long Covid. That's a big problem, but perhaps a little more manageable than predicting that everyone will eventually experience permanent damage from Covid-19.
In addition, we have debates about long-term effects on various organ systems, such as the article that found an increased risk of heart problems after Covid, or others that found the same problems with brain structure related to meaning. odor Usually shows similar results to symptom studies in terms of prevalence rates, but shows a proportion of people with underlying injuries who may not report symptoms in the survey*.
Since we're over 2,000 words long, it's tempting to wrap it all up in something short and sweet. Maybe "Long Covid is a big problem, but not as big as the headlines suggest", which is absolutely true, although perhaps a little off the mark.
But I won't do that. The key message is that this whole issue is complex, and anyone who says otherwise is probably wrong. In my opinion, studies with control groups give us a good idea of the proportion of people who experience long-term symptoms directly related to their Covid-19 infection - in this case it's probably somewhere between 1-10% of people. which are infected, perhaps less so. This share is also likely to decline significantly over time, although the exact rate of decline is difficult to estimate. That means we're still left with a large group of people who are experiencing symptoms even though they're not related to Covid-19 and don't have a good answer as to what's causing the problems - remember, over four hundred thousand people in the UK. That's not a small number! The problem may not be as dire as some headlines suggest, but it has chilling implications for our society.
It is hard to know how many people will get Long Covid after being infected with the coronavirus. What we do know is that it's a big problem.
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