Delta variant doubles Covid hospitalisation risk: Study

People infected with the SARS-CoV-2 Delta variant have approximately double the risk of hospitalisation compared with those infected with the Alpha variant, finds a new study.

The study, published in The Lancet Infectious Diseases journal, analysing more than 40,000 Covid-19 cases in the UK confirmed by virus genome sequencing finds a two-fold increased risk of hospitalisation from Delta versus Alpha variant infections.

"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," said researcher Gavin Dabrera, Consultant Epidemiologist at the National Infection Service, Public Health England.

"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," Dabrera added.

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, the UK.

For the study, the team analysed healthcare data from 43,338 positive Covid-19 cases in England between March 29 and May 23, 2021, including information on vaccination status, emergency care attendance, hospital admission, and other demographic characteristics.

In all cases included in the study, samples of the virus taken from patients underwent whole-genome sequencing to confirm which variant had caused the infection.

During the study period, there were 34,656 cases of the Alpha variant (80 per cent) and 8,682 cases of the Delta variant (20 per cent), the study indicated.

While the proportion of Delta cases in the study period overall was 20 per cent, it grew to account for around two-thirds of new Covid-19 cases in the week starting May 17, 2021 (65 per cent, 3,973/6,090), indicating it had overtaken alpha to become the dominant variant in England.

Around one in 50 patients were admitted to hospital within 14 days of their first positive Covid-19 test (2.2 per cent Alpha cases, 764/34,656; 2.3 per cent Delta cases, 196/8,682).

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).

Indicating the importance of vaccination, the team also emphasised that multiple studies have shown that full vaccination prevents both symptomatic infection and hospitalisation, for both Alpha and Delta variants.