A new peer-reviewed study published in the British Medical Journal is offering some of the first clear evidence to suggest the SARS-CoV-2 variant B.1.1.7, informally known as the UK variant, is linked with significantly higher rates of death than previously known strains of the virus.
In December last year public health authorities announced a novel strain of SARS-CoV-2 had been detected and labeled a "variant of concern" (VOC). Named B.1.1.7 the mutation became more anecdotally known as the UK variant.
The rapid spread of B.1.1.7 initially suggested this variant may be more transmissible than early iterations of the virus. And while it has become increasingly clear this UK variant is more infectious than previous strains, it has not been clear whether it presents with more severe forms of disease.
The new study looked at the mortality outcomes for over 50,000 demographically matched pairs of confirmed COVID-19 cases. Pairs were matched by a variety of factors including age, sex and location.
"We focussed our analysis on cases that occurred between November 2020 and January 2021, when both the old variants and the new variant were present in the UK,” explains Leon Danon, senior author on the study. “This meant we were able to maximize the number of "matches" and reduce the impact of other biases.”
The researchers calculated 227 deaths in the B.1.1.7 cohort compared to 141 deaths in matched subjects infected with earlier strains of the virus. This means the study suggests those infected with the UK variant were 64 percent more likely to die than those infected with prior viral strains.
Simon Clarke, from the University of Reading, says further work is needed to better understand what demographic factors may contribute to the UK variant’s increased lethality.
“While it is important to note that absolute risk remained low, increasing from 2.5 to 4.1 deaths per 1000 cases, this is substantially higher than the 30-40% possible increase reported by Sir Patrick Vallance on 22nd January, which was dismissed as unlikely in some quarters,” says Clarke, who did not work on this new study. “Unsurprisingly, the increase in lethality is largest in men and increases with age.”
Although reports of the UK variant’s increased mortality rate are still preliminary, this particular study from epidemiologists at the Universities of Exeter and Bristol is not an outlier. Another recent study, currently in pre-print and not yet peer-reviewed, from researchers at the London School of Hygiene and Tropical Medicine came to a similar conclusion calculating the UK variant presents with a 35 percent higher rate of mortality than other coronavirus strains.
An independent expert committee called NERVTAG (New and Emerging Respiratory Virus Threats Advisory Group) presented a report to the UK government several weeks ago and also concluded B.1.1.7 presents with greater cases of hospitalization and death than previous variants.
It is still unclear exactly how this particular SARS-CoV-2 variant is more lethal and some experts, such as Julian Tang from the University of Leicester, are not entirely convinced B.1.1.7 is more deadly. Tang, who did not work on the new study, suggests multiple confounding factors such as weather and personal behaviors across the last few months in the UK could account for the greater deaths.
“Again, I’m still not yet very convinced by these results,” says Tang. “… without the careful matching of comorbidities in the VOC [variant of concern] and non-VOC arms, these differential clinical severity model outcomes are still questionable.”
However, Leon Danon is confident in his team’s newly published findings. And while more research over time will inevitably bring greater insights into the UK variant’s severity, in the short-term Tang suggests this work is a vital reminder for public health organizations to be continuously monitoring new mutations and variants as they arise.
"SARS-CoV-2 appears able to mutate quickly, and there is a real concern that other variants will arise with resistance to rapidly rolled out vaccines,” says Tang. “Monitoring for new variants as they arise, measuring their characteristics and acting appropriately needs to be a key part of the public health response in the future."
The new study was published in the journal BMJ.
Source: University of Exeter