The B117 COVID-19 variant, which was first identified in the United Kingdom in October 2020, may pose a 61% higher risk of 28-day mortality, according to a study published today in Nature.
The finding is in line with last week's BMJ study that reported B117 had a 64% higher 28-day risk of death among people older than 30, although both studies note absolute 28-day mortality risk remains low for most populations.
"Crucially, our study is limited to individuals tested in the community," the researchers write. "However, this restricted focus allows us to capture the combined effect of an altered risk of hospitalisation given a positive test and an altered risk of death given hospitalisation, while only the latter would be measurable in a study of hospitalised patients only."
Absolute mortality risk increases with age
The researchers analyzed 2,245,263 positive COVID-19 community tests from all seven National Health Services regions in England from Sep 1, 2020, to Feb 14, 2021. About 0.8% (17,452) were fatal, and the researchers used Cox proportional hazard models to estimate increased 28-day risk of mortality.
Because only 51.1% of tests had conclusive S gene target failure (a mutation of B117, SGTF) status, however, the researchers estimated two risks: The first was solely for cases where SGTF status was known. The second was for all cases, and inverse probability weighting (IPW) helped compensate for missing data.
Almost 4,950 deaths in the study had known SGTF status, or 8.3% of the cohort's deaths and 9% of England's total COVID-19 deaths over the study period. After adjusting for factors such as demographics and testing date, the increased risk of 28-day mortality from B117 versus non-B117 COVID-19 strains was 55% (95% confidence interval [CI], 39% to 72%) among the verified status group and 61% (95% CI, 42% to 82%) for the whole cohort.
Going off the whole cohort's risk, this translates to a 28-day mortality rate of 0.9% for 55- to 69-year-old males, an absolute risk difference of 0.3 percentage points, as mortality rate for the original SARS-CoV-2 strain in this group is 0.6%. Other gender/age-group combinations, though showed more risk as age increased.
For instance, women and men 70 to 84 years old have increased B117 mortality rates of 4.4% (+1.5 percentage points compared with non-B117 strains) and 7.2% (+2.5 percentage points), respectively. Those 85 and above have an even greater risk of death when infected by B117 versus other COVID-19 strains, increasing 6 to 8 percentage points, for a mortality rate of 19% to 25%. The researchers add that only 44 deaths occurred in people 34 and younger during this period, so B117 mortality rates in this group could not be appropriately assessed.
"Our analysis suggests that B.1.1.7 is not only more transmissible than preexisting SARS-CoV-2 variants, but may also cause more severe illness," the researchers write. They acknowledge, however, that this study does not look at the possible mechanisms of the variant, which could affect data interpretation.