The findings come from a large study of 33,281 people in Scotland who tested positive for the coronavirus. Most of the results are consistent with those of earlier, smaller studies.
Of the 197 survivors of symptomatic SARS-CoV-2 infections who completed surveys at 12 months and 18 months, most reported persistent symptoms at both time points, the researchers reported in Nature Communications.
The rate of no recovery at 12 months was 11% with 51% partial recovery and 39% complete recovery. The rates at 18 months were 11% no recovery, 51% partial, and 39% complete recovery.
Asymptomatic infections were not associated with long-term COVID. But of the 31,486 people with symptomatic infections, nearly half reported incomplete recovery after six to 18 months.
A total of 3,744 participants with symptomatic infections completed a questionnaire twice in the following year. At six months, 8% reported no recovery, 47% reported partial recovery, and 45% reported full recovery. These percentages had hardly changed at 12 months: 8% reported no recovery, 46% partial recovery and 46% complete recovery.
One in 20 patients with a symptomatic infection reported no recovery at the most recent follow-up, the researchers said.
“Our research is important because it contributes to our long-term understanding of COVID in the general population, not just people who need to be hospitalized with COVID-19,” study leader Jill Pell of the University of Glasgow said in a statement.
Long COVID was more common in hospitalized patients and in the elderly, women, the socio-economically disadvantaged, and those with pre-existing health conditions. The most common persistent symptoms were respiratory distress, chest pain, palpitations and confusion, and “brain fog.”
Vaccination before infection was shown to protect against some symptoms in the long term, the researchers also found.
The researchers also surveyed nearly 63,000 individuals with only negative COVID tests to differentiate between health problems attributable to COVID-19 and health problems likely in the general population.