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While the term “long Covid” refers to a collection of long-term symptoms, the World Health Organization issued a standardised definition for the term in October 2020 to guide research.
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Estimates of long Covid prevalence vary widely – from as low as a quarter to as high as 80% – but experts told us that somewhere between 25 and 30% was “reasonable”.
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A systematic review released in November 2021 – but not peer-reviewed – estimated the overall prevalence of long Covid at 43%, but calculations of worldwide numbers need to reference truly global and current data.
The South African government has, as of 1 February 2022, relaxed its regulations to prevent the spread of Covid-19. Children have returned to school full time and asymptomatic patients no longer have to isolate.
In the third year of the pandemic, life appears to be returning to normal. But concerns have been raised about the long-term health implications of Covid-19 infections.
In an interview on Cape Talk radio, professor of physiology at South Africa’s Stellenbosch University, Resia Pretorius, described how people who had tested positive for Covid-19 experienced symptoms that lasted for months after the initial diagnosis.
“Between 25 and 30% of individuals will have these persistent symptoms,” said Pretorius. She is one of the authors of an August 2021 paper looking into the possible causes of “long Covid”.
In an article published by Cape Talk about the interview, the station said the number of people around the world thought to experience long Covid symptoms is estimated at “close to 100-million”.
Are these estimates accurate? We checked.
Pretorius told Africa Check her claim was based on a study conducted in late 2020 which found that among “individuals with Covid-19 who were followed up for as long as nine months after illness, approximately 30% reported persistent symptoms”.
Long Covid refers to a collection of symptoms that begin or continue to affect people long after they test positive for Covid-19. It’s also called long-haul Covid, post-Covid syndrome and post-acute Covid syndrome.
Common symptoms include fatigue, breathing difficulties and cognitive effects, like memory and attention problems. A wide variety of issues have been reported, with some research identifying more than 50 distinct symptoms.
In October 2020, the World Health Organization (WHO) published a standardised definition to guide research and clinical practice. It reads, in part: “Post Covid-19 condition occurs in individuals with a history of probable or confirmed SARS-CoV-2 infection, usually three months from the onset of Covid-19 with symptoms that last for at least two months and cannot be explained by an alternative diagnosis.”
How do we estimate the number of people with long Covid?
Estimates of the number of people suffering long-term effects of Covid-19 vary widely. There are a number of reasons for this.
The severity of initial illness of patients included in the studies varied. Some studies included only those who had been hospitalised, others included those who had had mild disease or were asymptomatic, while others included all three.
Studies have also often used different time periods when looking at long Covid. Symptoms that lasted anything from 14 to 120 days after infection have been categorised as long Covid. This was more common before the WHO introduced a standardised definition.
Number of unconfirmed cases must also be considered for full picture
Priya Duggal is an epidemiologist at Johns Hopkins University in Baltimore in the US. She told Africa Check that what kind of data was collected – and how – had an impact on the estimates of long Covid.
She emphasised that most studies only focused on those with a confirmed diagnosis of Covid-19. However, “early on in this pandemic, and again now with Omicron – not everyone has a confirmed diagnosis”.
Duggal said that this, combined with the fact that data often relied on hospital records or self reports to identify long Covid, meant we were likely not able to capture the full spectrum of the disease, which in turn made estimating prevalence tricky. As Duggal put it, “we are only as good as the questions we ask and who we ask them of”.
Do 25 to 30% of people really develop long Covid?
Despite the picture being hazy, Duggal believed broad approximations of prevalence were possible, and said a rate of “25 to 30% seems … reasonable for a definition of symptoms two to three months post infection”.
This approximate range is supported by a few specific studies, though the time periods used varied. In one very large US study, which included over 1.96 million people, around a quarter (23.2%) of people who had Covid-19 developed at least one long-term symptom 30 days or more after diagnosis.
Another large US-based study, involving 273,000 people, found the long Covid prevalence rate to be more than a third (37%) when defining the time period as three to six months after initial diagnosis. Data from 236,000 people in the US found a prevalence rate of 34% when looking only at neurological or psychiatric symptoms at six months after diagnosis.
In systematic reviews, where researchers combine the results of multiple studies, prevalence estimates vary considerably. One review, which largely investigated samples from North America, Europe and Asia, found that 43% of people will develop some form of long Covid. Another review, mostly including studies conducted in the US and UK, estimated the number to be much higher, at 80%.
Little known about long Covid in Africa
Shabir Madhi, professor of vaccinology and dean of the University of the Witwatersrand’s health sciences faculty in Johannesburg, South Africa, told us there was a large gap in the literature when it came to Africa.
“There has not been systematic follow-up to quantify the burden of long Covid in Africa,” he said.
Very little data exists on the prevalence of long Covid in the global south, for instance. “Global” prevalence estimates tend to come from data collected in the US, Europe and, to a lesser extent, Asia.
According to the author of the Cape Talk article, the claim that “100-million people globally” have some form of long Covid originated from a systematic review posted as a preprint in November 2021. A preprint is a scientific paper which has not yet been peer-reviewed. The review combined the results of 40 different studies to determine prevalence rates. (Note: Learn more about journals and peer-review here.)
The review defined long Covid as “at least one new or persisting symptom” 30 days or more after initial diagnosis. It found an overall prevalence of 43%, which varied considerably between the studies included. When the review was being conducted, an estimated 237 million people globally had contracted Covid-19.
The researchers estimated this meant around 100 million people had developed long Covid.
Since this review was posted in mid-2021, the total number of infections globally has climbed to around 401 million. If 43% of these cases developed into long Covid, the number of people who have developed long Covid would now stand at more than 172 million.
However, Duggal told Africa Check that “43% is a high estimate”. If a more conservative estimate of 25 to 30% was used, between 100 and 120 million people would have developed long Covid.
Until we have more data that uses a consistent, singular definition of long Covid and is truly global, the true prevalence will remain unknown.
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