The research was published recently in the journal Nature Communications. It was found that long-Covid symptoms were more likely following severe infections requiring hospitalisation.
The most reported long-COVID symptoms included breathlessness, chest pain, palpitations, and confusion, or 'brain fog', the researchers said.
Long-COVID was also more likely in individuals who were older, female and those from deprived communities, they said.
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The Long-CISS (COVID In Scotland Study) -- found that 1 in 20 people who took part in the research had not recovered from having COVID-19 at their most recent follow up -- between six and 18 months following infection with SARS-CoV-2.
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The CISS study was set up in May 2021 to understand the long-term impact of COVID-19, and compare it with the health and wellbeing of people who had not yet been infected.
The study is led by the University of Glasgow in collaboration with Public Health Scotland, the NHS in Scotland, and the Universities of Aberdeen and Edinburgh.
The initial results from the ongoing study, found that, overall, 42 per cent of people infected with COVID-19 reported feeling only partially recovered between six- and 18-months following infection.
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Details of each person's partial recovery were not given in the survey but could include a range of symptoms from mild to moderate and may not necessarily result in a long COVID diagnosis.
The researchers found that those with asymptomatic infection had no long-term impact; and people who had been vaccinated prior to infection with COVID-19 appeared to have protection from some long-term symptoms.
However, the study found that the impact for people with long-COVID were wide-reaching, with a wide-range of symptoms, impacts on all aspects of daily life and reduced overall quality of life.
In addition, those with pre-existing physical and mental health problems, such as respiratory disease and depression, were also more likely to experience long-COVID.
The study found that whilst recovery status remained constant over the follow-up period for most participants, 13 per cent of people reported improvement over time and 11 per cent reported some deterioration.
The CISS study used a Scottish population group of 33,281 laboratory-confirmed SARS-CoV-2 infections, and matched them with 62,957 never-infected individuals from the general population.
Both groups were followed-up via six, 12 and 18-month questionnaires, with researchers able to link to hospitalisation and death records.
Using NHS health data records, all Scottish adults who had a positive COVID-19 test, as well a sample of people who tested negative for the disease, were sent an SMS message inviting them to take part in the CISS study.
Individuals were then asked to answer questions online about their health, both before and after COVID-19, to determine whether the virus has had any lasting effects on their lives.
"While most people recover quickly and completely after infection with COVID-19, some people develop a wide variety of long-term problems," said Jill Pell, Professor of Public Health at the University of Glasgow, who leads the study.
"Therefore, understanding long-COVID is essential to inform health and social care support," Pell said.
The study is important because it adds to our understanding of long-COVID in the general population, not just in those people who need to be admitted to hospital with COVID-19.
By comparing symptoms with those uninfected, the researchers were able to distinguish between health problems that are due to COVID-19 and those that would have happened anyway.
"This study provides novel and important evidence on long-COVID in Scotland," said Andrew McAuley, Consultant Healthcare Scientist at Public Health Scotland.
"We know that being fully vaccinated against COVID-19 can reduce the likelihood of developing long-COVID and therefore we encourage those who are eligible for the COVID vaccine to take the opportunity to enhance their protection by getting vaccinated," McAuley added.
(With inputs from PTI)
