The latest findings of the world’s biggest study into ‘Long Covid’ in children and young people (CYP) – the CLoCk study from University College London – have been published as a pre-print.
Surveying 11 to 17 year-olds who tested positive for COVID-19 in England between September and March, the researchers found that the condition is not common in children and young people. This is in line with other studies into Long Covid.
As with earlier studies, symptoms were prevalent in those who tested negative as well as those who tested positive, complicating the picture of the condition which the authors acknowledge lacks clear definition.
Further confusion was sown by the fact that reported symptoms increased rather than decreased after three months, leaving the authors puzzling over the explanation.
Three months after the SARS-CoV-2 test, the presence of physical symptoms was higher than at the time of testing. This finding emphasises the importance of having a comparison group to objectively interpret the findings and derive prevalence estimates. Although 64.6% of test-positives reported no symptoms at time of testing (compared to 91.7% of test-negatives), they did not continue to remain asymptomatic, with only 33.5% of test-positives (and 46.7% of test-negatives) reporting no symptoms at three months. This finding warrants further exploration and could be due to self-selection into the study because they were experiencing on-going symptoms, recall bias, external factors relating to the pandemic such as returning to school and exposure to other sources of infection, and the actual trajectory of the illness, although this wouldn’t explain the high prevalence among test-negative CYP.
In terms of physical symptoms – tiredness, headaches, shortness of breath, loss of smell, and so on – the researchers found there was a somewhat elevated prevalence of these among the test-positive compared to the test-negative, though both had increased over the three month period.
Three months after the SARS-CoV-2 test, the presence of physical symptoms was higher than at baseline in both groups; 66.5% of test-positives and 53.4% of test-negatives had any symptoms whilst 30.3% of test-positives and 16.2% of test-negatives had 3+ symptoms. The symptom profile did not vary by age: for both 11-15 year-olds and 16-17 year-olds the most common symptoms among test-positives were tiredness, headache and shortness of breath and, among test-negatives, tiredness, headache and the unspecified category of “other”. Again, the prevalence of tiredness and headache was consistently higher in the test positives, 39.0% and 23.2% versus 24.4% and 14.2% in negatives, respectively. Prevalence was higher for 16-17 year-olds; for example, 46.4% of test-positives reported being tired compared to 29.6% of test-negatives.
The 14% difference reported here between the 30% of test-positives and the 16% of test-negatives who had three or more symptoms at three months is likely to be the study’s most accurate estimate of the prevalence of Long Covid in the sample population.
However, as the BBC’s Nick Triggle notes, the low response rate and selection bias towards the unwell in the survey may mean the true prevalence of Long Covid is more like 2%.