The Covid-19 variant first detected in Kent does not increase the severity of the disease, but it is more transmissible, research has found.
Studies of the variant, which is now dominant in the UK and several other countries, found no evidence that it causes more severe symptoms, or increases the risk of developing long Covid, than other strains of the virus.
While the variant does not make symptoms worse, studies found that the viral load and reproduction (R) number were higher for the Kent variant, also known as B117, adding to growing evidence that it is more transmissible than the first strain detected in Wuhan, China, in December 2019.
One observational study of patients in London hospitals suggested it is not associated with more severe illness and death, but appears to lead to higher viral load.
A separate study, using data logged by 37,000 UK users of a self-reporting coronavirus symptom app, also found no evidence that the variant altered symptoms or likelihood of experiencing long Covid.
However, authors of both studies acknowledged that the findings differ from some other studies and called for more research to be conducted.
No evidence of increased disease severity
Findings from the studies, conducted between September and December, provide further insights into the variant’s characteristics that will help to inform public health, clinical and research responses to this and other variants.
A paper in The Lancet Infectious Diseases journal is a whole-genome sequencing and cohort study involving coronavirus patients admitted to University College London Hospital and North Middlesex University Hospital between November 9 and December 20.
The authors compared illness severity in people with and without B117 and calculated viral load.
Among 341 patients who had their test swabs sequenced, 58 per cent (198 out of 341) had B117 and 42 per cent (143 out of 341) had a non-B117 infection.
Researchers found no evidence of an association between the variant and increased disease severity, with 36 per cent (72 out of 198) of B117 patients becoming severely ill or dying, compared with 38 pe cent of those with a different strain.
Those infected with the variant were no more likely to die than patients with a different strain, according to the study.
Dr Eleni Nastouli, from University College London Hospitals NHS Foundation Trust and the UCL Great Ormond Street Institute of Child Health, said: “One of the real strengths of our study is that it ran at the same time that B117 was emerging and spreading throughout London and the South of England.
“Analysing the variant before the peak of hospital admissions and any associated strains on the health service gave us a crucial window of time to gain vital insights into how B117 differs in severity or death in hospitalised patients from the strain of the first wave.
“Our study is the first in the UK to utilise whole-genome sequencing data generated in real time and embedded in an NHS clinical service and integrated granular clinical data.”
A second study, published in The Lancet Public Health, analysed self-reported data from 36,920 UK users of the Covid Symptom Study app who tested positive for the disease between September 28 and December 27.
The analysis covered 13 full weeks over the period when the proportion of B117 grew most notably in London, the South East and East of England.
Users were included in a week if they had reported a positive test during the 14 days before or after that week.
For each week in every region in the analysis (Scotland, Wales and the seven NHS England regions), authors calculated the proportion of users reporting any of 14 Covid-19 symptoms.
Dr Claire Steves, reader and honorary consultant physician at King’s College London, who co-led the study, said: “We could only do this by aggregating two large sources of data: the extensive genetic sequencing of viral strains performed in the UK, and symptom and testing logs from millions of users on the Covid Symptom Study App.
“Thanks to them, we confirmed the increased transmissibility but also showed that B117 clearly responded to lockdown measures and doesn’t appear to escape immunity gained by exposure to the original virus.
“If further new variants emerge, we will be scanning for changes in symptom reporting and reinfection rates, and sharing this information with health policymakers.”