Study suggests Delta more than doubles death risk

A Canadian study has given more evidence of the much sharper virulence of SARS-CoV-2 variants of concern, with the Delta strain appearing to be the most dangerous yet.
 
The greater contagiousness of the Delta variant was clearly understood early on in its progression to becoming the dominant strain around the world. However, the large study carried out by researchers at the University of Toronto seems to reinforce evidence suggesting the variant also poses a greater risk of more severe outcomes, including in younger age groups.
 
Published this week in the Canadian Medical Association Journal, the research tracked 212,326 cases of COVID-19 recorded between 7 February and 26 June this year in the Canadian province of Ontario.
 
It found the chances of death were 133% higher with the Delta variant compared to the original strain, while the hospitalisation risk rose by 108% and the probability of ICU admission increased by 235%.
 
The Delta variant was detected in Ontario in April after the study begun and only became the dominant strain in July after the study period had ended. Confidence intervals for the risks attributed to Delta are higher compared to the figures presented for the other variants.
 
However, the authors say the results clearly signal Delta’s greater virulence and its increased risk of causing more severe outcomes.
 
‘Given the relatively small number of Delta infections in our study, it is remarkable that we detected a clear and significant elevated risk of uncommon, delayed outcomes, such as death,’ they write.
 
According to the research, other variants of concern also increased risks but not as substantially.
 
With COVID-19 cases caused by the Alpha, Beta and Gamma variants of concern, the study found the risk of hospitalisation increased by 52%, the likelihood of admission to ICU rose by 89% and the chances of death were 51% higher.
 
‘Once we adjusted for confounding factors such as age, vaccination status, comorbidity and temporal trends, elevated per-infection risk, including risk of death, remained markedly higher with variants of concern, and with the Delta variant in particular,’ the authors write.
 
The researchers cite the risk of mutations as one of the biggest challenges in the global fight against the pandemic.
 
‘The emergence of novel SARS-CoV-2 [variants of concern] has slowed progress against the pandemic in three distinct ways,’ the article reads.  
 
‘Namely by increasing transmissibility and the virus’ reproduction number, by increasing immune escape and diminishing vaccine effectiveness, and by increasing the virulence of SARS-CoV-2 infection.’
 
The authors’ findings also appear to corroborate previous warnings in recent months that the Delta variant is having a greater effect on younger people than previously seen in the pandemic.
 
Even though people infected with variants of concern were younger on average and less likely to have comorbidities, the authors wrote they had ‘higher crude risks of hospitalisation and ICU admission’.
 
When the current Australian Delta outbreaks were in their relative infancy, infectious disease experts were already flagging signs of the increased risks it might pose to younger people.
 
Professor Tony Cunningham of the Westmead Institute for Medical Research in Sydney described the strain to Nine Newspapers as ‘clearly more virulent’ and that it was ‘causing serious disease in younger people’.
 
Likewise, a July media release from the Australian Technical Advisory Group on Immunisation (ATAGI) about the use of COVID-19 vaccines in an outbreak setting noted Delta’s greater contagiousness, although it did not reach a firm position on whether it caused more severe disease.
 
‘Some countries have reported that infections with this variant are associated with higher risk of hospitalisation, need of intensive care, and death, even after differences in age or other factors are accounted for,’ the ATAGI statement read.
 
The authors of the Canadian Medical Association Journal article also highlight the impact of vaccination in reducing the risks, both against the original strain and the emerging variants, which they say is helping to minimise the impact.
 
‘The effects reported here represent a substantial degree of protection against death conferred by vaccines [about 80%–90%], even when they fail to prevent infection,’ the authors write.
 
‘Vaccination has undoubtedly blunted the impact of these variants of concern. We found a marked reduction in risk of severe disease and death among both partially and fully vaccinated people in our study.’
 
It is the latest of several publications that have signalled the enhanced risks of severe disease presented by Delta.
 
According to a technical briefing published by Public Health England in August, people who have had COVID-19 before are more likely to be reinfected with the Delta strain than with previous SARS-CoV-2 variants of concern.
 
A national study, also from data in England, was published in The Lancet Infectious Diseases journal in the same month, suggesting that Delta noticeably increased the number of hospital admissions and ICU attendance compared to previous variants.
 
A pre-print study of patients in Singapore, meanwhile, found as far back as June that infection with the Delta strain was linked to ‘higher odds of oxygen requirement, ICU admission, or death’.
 
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