About 13% Covid-Positive Adults Develop Long Covid Symptoms, Study In Lancet Says Citing ‘Most Reliable’ Estimates

The study provides one of the first comparisons of long-term symptoms after SARS-CoV-2 infection with symptoms in an uninfected population.

A 'Long Covid' patient during a digital therapy in Berlin. The patient was a nurse who became infected with Covid-19 in 2020, and has been experiencing Long Covid symptoms ever since ( Image Source :Getty )

About 13 per cent adults infected with Covid-19 experience 'long Covid' symptoms, says a large Dutch study published today in The Lancet. This is equivalent to one in eight adults infected with SARS-CoV-2. 

When the symptoms of Covid-19 persist in a patient for weeks, months, and even a year, in spite of testing negative for the virus, the condition is known as 'long Covid' or 'post-Covid syndrome'.

According to an article published on the Harvard Health website, the points that should be taken into consideration to define 'long Covid' are, a medical diagnosis of Covid-19 on the basis of symptoms and a diagnostic testing for the virus, the patient not having returned to the pre-Covid level of health and function even after a period of six months, and a patient suffering from symptoms suggesting long Covid but not evidently suffering from permanent damage to the heart, kidneys, and lungs. 

The World Health Organization (WHO) says that people with long Covid are not infectious to others if they are not carrying the virus. This persistent state of illness can be termed as 'post Covid condition', 'chronic Covid syndrome', 'late sequelae of Covid-19', 'long haul Covid', 'post-acute Covid-19', among other names. 

What Makes The Dutch Study Special?

The Dutch study published in The Lancet provides one of the first comparisons of long-term symptoms after SARS-CoV-2 infection with symptoms in an uninfected population, and has also measured symptoms in individuals both before and after Covid-19 infection. Since uninfected populations have been included, it enables a more accurate prediction of long-term Covid-19 symptom prevalence and an improved identification of the core symptoms of long Covid, a statement released by The Lancet says.

Limitations In Previous Studies On Long Covid

Patients often report various symptoms after recovery from acute Covid-19, but previous studies on ‘post-Covid-19 condition’ have not corrected for the prevalence and severity of these common symptoms before Covid-19 and in populations without SARS-CoV-2 infection, the study says. 

The authors note in the study that they aimed to analyse the nature, prevalence, and severity of long-term symptoms related to Covid-19.

Professor Judith Rosmalen, the lead author on the paper, said in the statement that there is an urgent need for data informing the scale and scope of the long-term symptoms experienced by some patients after Covid-19 illness. She added that most previous research into long Covid has not looked at the frequency of these symptoms in people who have not been diagnosed with Covid-19 or looked at individual patients' symptoms before the diagnosis of Covid-19. 

New Study Looks At Symptoms Associated With Long Covid In Uninfected Individuals As Well

Rosmalen further said that the approach of the new study looks at the symptoms most often associated with long Covid, including breathing problems, fatigue and loss of taste and smell, both before a Covid-19 diagnosis and in people who have not been diagnosed with Covid-19. The method allows the researchers to take pre-existing symptoms and symptoms in non-infected people into account to offer an improved working definition for long Covid and provide a "reliable estimate" at how likely long Covid is to occur in the general population.

How Was The Study Conducted?

The new study was conducted in the Netherlands. As part of the study, the researchers collected data by asking participants of the population-based Lifelines Covid-19 Cohort to regularly fill out digital questionnaires on 23 symptoms commonly associated with long Covid. Between March 2020 and August 2021, the researchers sent the questionnaire 24 times to the same individuals. This means that the participants who had Covid-19 during this period were infected with the Alpha variant or earlier variants of SARS-CoV-2, the study says. 

If the participants had a positive test or a doctor's diagnosis of Covid-19, they were recorded as Covid-19 positive. As many as 76,422 people had participated in the study. Of these, 4,231 participants who had Covid-19 were matched to 8,462 controls. In other words, 5.5 per cent participants had Covid-19.

The study authors took into account sex and age, and the time of completing questionnaires that indicated a Covid-19 diagnosis.

All the Lifelines participants involved in the study were aged 18 years or older. 

Core Symptoms Of Long Covid

Several symptoms were new or more severe three to five months after becoming infected with SARS-CoV-2, compared to symptoms before being diagnosed with coronavirus, and to a control group. This suggests that the symptoms can be considered the core symptoms of long Covid, the study says.

According to the study, the core symptoms are chest pain, difficulty breathing, pain when breathing, painful muscles, tingling hands and feet, general tiredness, loss of taste, loss of smell, heavy arms and legs, alternate episodes of feeling hot and cold, and a lump in the throat. Three months after infection, the severity of the symptoms plateaued and there was no further decline. 

Headache, nausea, dizziness, itchy eyes, and back pain were the symptoms that did not increase significantly three to five months after a Covid-19 diagnosis. 

Aranka Ballering, the first author on the paper, said these core symptoms have major implications for future research. This is because these symptoms can be used to distinguish between ‘post Covid-19 condition’ and non-Covid-19-related symptoms. 

Percentages Of People Experiencing Long Covid Symptoms 

As many as 1,782 study participants had submitted pre-Covid symptom data. Of these, 381 participants or 21.4 per cent of the Covid-19 positive patients experienced at least one increased core symptom at moderate severity three months or more after SARS-CoV-2 infection, compared to 8.7 per cent of the control group. There were 4,130 participants in the control group. 

Ballering further said that by looking at symptoms in an uninfected control group and in individuals both before and after SARS-CoV-2 infection, the study authors were able to take into account symptoms which may have been a result of non-infectious disease health aspects of the pandemic, such as stress caused by restrictions and uncertainty.

She added that 'Post-Covid-19 condition', otherwise known as long Covid, is an urgent problem with a mounting human toll, and understanding the core symptoms and the prevalence of post-Covid-19 in the general population represents a major step forward for researchers' ability to design studies that can ultimately inform successful healthcare responses to the long-term symptoms of Covid-19.

Overall Findings And Interpretation

Therefore, the researchers found that of the 76,422 study participants, 4231 had Covid-19. They were compared to 8462 controls. According to the study, persistent symptoms in Covid-19-positive participants at 90 to 150 days after Covid-19 compared with symptoms before Covid-19 and with matched controls included chest pain, difficulties breathing, tingling extremities, lump in throat, pain when breathing, painful muscles, general tiredness, and heavy arms or legs. 

These symptoms could be attributed to Covid-19 in 12.7 per cent of patients. Out of 1,782 Covid-19-positive participants, 381 persons had at least one of these core symptoms substantially increased to at least moderate severity at 90 to 150 days after Covid-19 diagnosis. Meanwhile, 361 of 4,130 Covid-19-negative controls experienced at least one of these core symptoms at least moderate severity at 90 to 150 days after being diagnosed with Covid-19.

The study authors conclude that this is the first study to report the nature and prevalence of post-Covid-19 condition, while correcting for individual symptoms present before Covid-19 and the symptom dynamics in the population without SARS-CoV-2 infection during the pandemic. 

Rosmalen said future research should include mental health symptoms such as depression and anxiety symptoms, along with additional post-infectious symptoms that the authors could not assess in the study, such as brain fog, insomnia, and post-exertional malaise. She added that the authors were unable to investigate what might cause any of the symptoms observed after Covid-19 in the study, but they hope future research will be able to give insights into the mechanisms involved.

Limitations To The Study

According to the authors, the limitations to the study include the fact that only patients with the Alpha variant or earlier variants of SARS-CoV-2 were considered. The study did not include data from people during the period when the Delta or Omicron variants were causing most infections. 

Though symptoms such as brain-fog are identified as potentially relevant for a definition of long Covid, the study did not consider these symptoms. Another limitation is that the study was conducted in one region and did not include an ethnically diverse population.

Due to the timing of the study, the authors were unable to assess the effect of Covid-19 vaccination and different SARS-CoV-2 variants on long Covid symptoms, Rosmalen said. 

"We hope future studies will provide answers on the impacts of these factors," she concluded.