People infected with the Covid-19 delta variant are twice as likely to be taken to hospital than those infected with the alpha variant, a study has found.
The risk of being admitted to hospital at an early stage was also higher, researchers found in the largest study to date, in which 40,000 cases in England were analysed.
The findings suggest that outbreaks of the delta variant are likely to lead to a greater burden on health services than the alpha strain, particularly in unvaccinated people and other vulnerable populations.
The study also suggested there was an increased risk of hospital among unvaccinated or partially vaccinated people, since these people made up the majority of cases in the study.
The study was carried out by researchers from Public Health England and the University of Cambridge and published in The Lancet Infectious Diseases.
Dr Gavin Dabrera, one of the study’s lead authors and a consultant epidemiologist at the National Infection Service, Public Health England, said: “This study confirms previous findings that people infected with delta are significantly more likely to require hospitalisation than those with alpha, although most cases included in the analysis were unvaccinated.
"We already know that vaccination offers excellent protection against delta and as this variant accounts for over 98 per cent of Covid-19 cases in the UK, it is vital that those who have not received two doses of vaccine do so as soon as possible.”
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The delta variant was first reported in India in December 2020 and early studies found it to be up to 50 per cent more transmissible than the variant of Covid-19 that had previously gained dominance worldwide, known as the alpha variant, first identified in Kent, England.
A preliminary study from Scotland previously reported a doubling in risk of a hospital stay with the delta variant compared with the alpha variant and it is suspected that delta is associated with more severe disease.
In the latest study, researchers analysed healthcare data from 43,338 positive Covid-19 cases in England between 29 March and 23 May, such as information on vaccination status, emergency care attendance and hospital admission.
Around one in 50 patients were admitted within 14 days of their first positive Covid-19 test. After accounting for factors that are known to affect susceptibility to severe illness from Covid-19, including age, ethnicity and vaccination status, the researchers found the risk of being admitted to hospital was more than doubled with the delta variant compared with the alpha variant (2.26-fold increase in risk).
Dr Anne Presanis, one of the study’s lead authors and senior statistician at the MRC Biostatistics Unit, University of Cambridge, said: "Our analysis highlights that in the absence of vaccination, any delta outbreaks will impose a greater burden on healthcare than an alpha epidemic.
"Getting fully vaccinated is crucial for reducing an individual’s risk of symptomatic infection with delta in the first place, and, importantly, of reducing a delta patient’s risk of severe illness and hospital admission.”
