One in eight adults who are infected with SARS-CoV-2 experience long-term symptoms due to Covid-19, according to a large Dutch study published in The Lancet.

It is one of the first comparisons of long-term symptoms after SARS-CoV-2 infection (often called ‘long-Covid’) with symptoms in an uninfected population, said a note on the study that measures symptoms in individuals both pre- and post-Covid-19 infection.

The inclusion of uninfected populations enables a more accurate prediction of the long-term Covid-19 symptom prevalence as well as improved identification of the core symptoms of long-Covid, it added..

Prof Judith Rosmalen, with the University of Groningen and the lead author of the study, said, “Our study approach looks at the symptoms often associated with long-Covid, including breathing problems, fatigue and loss of taste and/or smell, both before a Covid-19 diagnosis and in people who have not been diagnosed with Covid-19. This method allows us 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 this is to occur in the general population.”

The research is done in Netherlands, and researchers collected data by asking participants of the population-based Lifelines Covid-19 cohort (a multigenerational group) to regularly fill out digital questionnaires on 23 symptoms commonly associated with long-Covid.

The questionnaire was sent out 24 times to the same individuals between March 2020 and August 2021 meaning participants who had Covid-19 during this time were infected with the SARS-CoV-2 alpha-variant or earlier variants. Most of the data was collected before the Covid-19 vaccine rollout in the country, so the number of vaccinated participants was too small to analyse in this study, it added. .

The researchers found that several symptoms were new or more severe three to five months after having Covid-19, compared to symptoms before a Covid-19 diagnosis and to the control group, suggesting these symptoms can be viewed as the core symptoms of long Covid., the note explained.

The core symptoms recorded were chest pain, difficulties in breathing, pain when breathing, painful muscles, loss of tase and/or smell, tingling hands/feet, a lump in throat, alternately feeling hot and cold, heavy arms and/or legs and general tiredness. The severity of these symptoms plateaued at three months after infection with no further decline. Other symptoms that did not significantly increase three to five months after a Covid-19 diagnosis included headache, itchy eyes, dizziness, back pain and nausea.

Study limitations

The authors acknowledged the limitations in the study, including the fact that the patients had no data from people infected during the period when the delta or omicron variants were causing most infections. Additionally, due to asymptomatic infection, the prevalence of Covid-19 in this study may be underestimated. Another limitation to this study is that since the beginning of data collection other symptoms, such as brain-fog, have been identified as potentially relevant for a definition of long Covid but this study did not look at these symptoms. Furthermore, the study was undertaken in one region and did not include and ethnically diverse population.