Getting sick with the Delta variant doubles hospitalization risk compared with Alpha, a large study of mostly unvaccinated people shows

• The Delta variant doubled the risk of hospitalization compared to the formerly-dominant Alpha variant.
• About 74% of people in the UK-based study were unvaccinated, and few were fully vaccinated.
• The study authors said it was "crucial" to get people fully vaccinated to protect against Delta.

People who get sick with the Delta variant of the novel coronavirus have more than twice the risk of being hospitalized compared with those who catch the Alpha variant, a large UK study suggests.

Scientists from Cambridge University and Public Health England who led the study, said in a statement Friday that Delta could be a "greater burden" on health services than the Alpha variant, "particularly in unvaccinated people and other vulnerable populations".

The paper, published in the Lancet Infectious Diseases medical journal late on Friday, analyzed 43,340 COVID-19 cases. About 74% of the cases were in people who were unvaccinated, while less than 2% were in people who were fully vaccinated. The rest were in partially vaccinated individuals.

Delta is more infectious and increases your risk of hospitalization

Overall, just over 2% of people who contracted COVID-19 were hospitalized within 14 days of testing positive. The researchers found that the risk of being hospitalized was 2.26 times greater for people who were sickened by the Delta variant, compared with Alpha, taking into account factors that may affect someone's propensity to develop severe COVID-19, such as age, gender, ethnicity and socioeconomic factors. They didn't take into account pre-existing medical conditions.

The study's findings are focused on the risks to unvaccinated and partially vaccinated people. The authors said that they were unable to draw firm conclusions about whether Delta increases the risk of hospitalization in vaccinated people, because there weren't enough vaccinated people admitted to the hospital with COVID-19 during the study period.

Other research has shown that fully vaccinated people have strong protection against being hospitalized, should they become sick with the Delta variant.

Delta is at least 50% more infectious than the Alpha variant, which overwhelmed UK hospitals over Christmas, and has additional mutations that help it avoid the immune response.

The study is the largest to date and first to look at the genetic code of the virus in the lab to determine the variant - the most accurate technique.

Delta was detected in the UK in March and overtook Alpha as the dominant variant in June . The proportion of Delta tests increased from 20% to 74% during the study period, which ran from March 29 to May 23, the authors said. Overall, they looked at 8,682 Delta cases and 34,656 Alpha cases.

The study confirms previous data from Scotland in June that found Delta increased the risk of hospitalization compared with Alpha. The Scottish researchers used a proxy measure to determine the variant that caused COVID-19.

Vaccines are 'crucial'

Dr. Anne Presanis, one of the study's lead authors, said in a statement Friday that getting fully vaccinated was "crucial" to protect against Delta. "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," she said.

Dr. David Strain, senior clinical lecturer at University of Exeter, said in a statement to the Science Media Centre on Friday that the study confirmed what "we are seeing in clinical practice." Strain wasn't involved in the research.

"In addition to the Delta variant being more infectious than the original or the Alpha variants, it is also causing more severe illness, in populations that previously would have had only mild infections," he said.