a large study published in The Lancet indicates.
The researchers determined that percentage by comparing long-term symptoms in people infected by SARS-CoV-2 with similar symptoms in uninfected people over the same time period.
Among the group of infected study participants in the Netherlands, 21.4% had at least one new or severely increased symptom 3-5 months after infection compared with before infection. When that group of 21.4% was compared with 8.7% of uninfected people in the same study, the researchers were able to calculate a prevalence 12.7% with long COVID.
“This finding shows that post–COVID-19 condition is an urgent problem with a mounting human toll,” the study authors wrote.
The research design was novel, two editorialists said in an accompanying commentary.
Christopher Brightling, PhD, and Rachael Evans, MBChB, PhD, of the Institute for Lung Health, University of Leicester (England), noted: “This is a major advance on prior long COVID prevalence estimates as it includes a matched uninfected group and accounts for symptoms before COVID-19 infection.”
Symptoms that persist
The Lancet study found that 3-5 months after COVID (compared with before COVID) and compared with the non-COVID comparison group, the symptoms that persist were chest pain, breathing difficulties, pain when breathing, muscle pain, loss of taste and/or smell, tingling extremities, lump in throat, feeling hot and cold alternately, heavy limbs, and tiredness.
The authors noted that symptoms such as brain fog were found to be relevant to long COVID after the data collection period for this paper and were not included in this research.
Researcher Aranka V. Ballering, MSc, PhD candidate, said in an interview that the researchers found fever is a symptom that is clearly present during the acute phase of the disease and it peaks the day of the COVID-19 diagnosis, but also wears off.
Loss of taste and smell, however, rapidly increases in severity when COVID-19 is diagnosed, but also persists and is still present 3-5 months after COVID.
Ms. Ballering, with the department of psychiatry at the University of Groningen (the Netherlands), said she was surprised by the sex difference made evident in their research: “Women showed more severe persistent symptoms than men.”
Closer to a clearer definition
The authors said their findings also pinpoint symptoms that bring us closer to a better definition of long COVID, which has many different definitions globally.
“These symptoms have the highest discriminative ability to distinguish between post–COVID-19 condition and non–COVID-19–related symptoms,” they wrote.
Researchers collected data by asking participants in the northern Netherlands, who were part of the population-based Lifelines COVID-19 study, to regularly complete digital questionnaires on 23 symptoms commonly associated with long COVID. The questionnaire was sent out 24 times to the same people between March 2020 and August 2021. At that time, people had the Alpha or earlier variants.
Participants were considered COVID-19 positive if they had either a positive test or a doctor’s diagnosis of COVID-19.
Of 76,422 study participants, the 5.5% (4,231) who had COVID were matched to 8,462 controls. Researchers accounted for sex, age, and time of completing questionnaires.