Delta variant nearly doubles risk of hospitalization, study finds

Nurses check on a Covid-19 patient in the critical care unit of Royal Papworth Hospital in Cambridge, England on March 17.
Nurses check on a Covid-19 patient in the critical care unit of Royal Papworth Hospital in Cambridge, England on March 17. Joe Giddens/PA Images/Getty Images

The Delta variant, which is also known as B1.617.2 and was first identified in India, is associated with approximately double the risk of hospitalization compared with the Alpha variant (or B.1.1.7) first identified in the UK, according to the preliminary findings of a Scottish study published Monday in The Lancet. 

A research team from the Universities of Edinburgh and Strathclyde and Public Health Scotland analyzed data from 5.4 million people in Scotland as part of the “EAVE II” project. The study comes after Health Secretary Matt Hancock announced last week the Delta variant makes up 91% of new cases in the UK.

During the period included in the study, April 1 to June 6, there were 19,543 community cases and 377 hospitalizations, according to the study. Among those, 7,723 cases and 134 hospitalizations were found to be the Delta variant. Risk of admission was “particularly increased in those with five or more relevant comorbidities,” the study says. 

The early findings suggest two Covid-19 vaccine doses provide protection against the Delta variant, but it may be a lower level of protection than against the Alpha variant. Vaccines were found to reduce the risk of being admitted to hospital, but strong protective effects against the Delta variant were not seen until at least 28 days after the first vaccine dose, the study added.

The Pfizer-BioNTech vaccine was found to provide 79% protection against infection from the Delta variant, compared with 92% against the Alpha variant, in community cases at least two weeks after the second dose.

“For the same scenario, the Oxford-AstraZeneca vaccine offered 60 per cent protection against infection with the Delta variant compared with 73 per cent for the Alpha variant. This lower vaccine effect may reflect that is takes longer to develop immunity with Oxford-AstraZeneca,” a news release from the universities added. However, the research team urged caution when it comes to comparing vaccines because of the observational nature of the study. 

“Over a matter of weeks the Delta variant has become the dominant strain of SARS-CoV-2 in Scotland. It is unfortunately associated with increased risk of hospitalization from Covid-19. Whilst possibly not as effective as against other variants, two doses of the Pfizer-BioNTech and Oxford-AstraZeneca vaccines still offer substantial protection against the risk of infection and hospitalization. It is therefore really important that, when offered second doses, people take these up both to protect themselves and to reduce household and community transmission,” professor Aziz Sheikh, director of the University of Edinburgh’s Usher Institute and EAVE II study lead, said in a statement.

The findings of the research were released ahead of an announcement from UK Prime Minister Boris Johnson about a potential delay to the lifting of all social contact restrictions in England, with the government suggesting this will allow more time for people to receive two doses of the vaccine.   

“It is important to recognize that these are preliminary results using rapidly accessible data. A fuller understanding will come when the results presented here are combined with similar analyses from other data sets in the UK,” professor Chris Robertson of Strathclyde University added.