The coronavirus variant first detected in Kent, and now dominant in the UK and a number of other countries, is more transmissible but does not increase disease severity, research has suggested.
Two studies found no evidence that people with the B117 variant have worse symptoms or a heightened risk of developing long Covid then those with a different strain.
However, viral load and the reproduction (R) number were higher for B117, adding to growing evidence that it is more transmissible than the first strain detected in Wuhan, China, in December 2019, the research indicates.
One observational study of patients in London hospitals suggested the variant is not associated with more severe illness and death, but appears to lead to higher viral load.
A separate observational study using data logged by 37,000 UK users of a self-reporting coronavirus symptom app found no evidence the variant altered symptoms or likelihood of experiencing long Covid.
Authors of both studies acknowledged the findings differ from some other studies exploring the severity of the variant, and called for more research.
The emergence of variants has raised concerns about whether they could spread easily and be more deadly, and that vaccines might be less effective against them.
Findings from the new studies, conducted between September and December when B117 emerged and started to spread across parts of England, provide insights into its characteristics that will help 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% (198 out of 341) had B117 and 42% (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% (72 out of 198) of B117 patients becoming severely ill or dying, compared with 38% of those with a different strain.
According to the study, those with the variant were no more likely to die than patients with a different strain, with 16% (31 out of 198) dying within 28 days compared with 17% (24 out of 141) for those with a non-B117 infection.
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.”
The analysis revealed no statistically significant associations between the proportion of B117 within regions and the type of symptoms people experienced.
However, the authors found that the variant increased the overall R number by 1.35 times compared with the original strain.
This estimate is similar to those from other studies investigating the variant’s transmissibility.