Covid-19 patients infected with the Delta variant had about double the risk of hospitalization compared to those infected with the Alpha variant, according to the study published Friday in the journal Lancet Infectious Diseases.

"The results suggest that patients with the Delta variant had more than two times the risk of hospital admission compared with patients with the Alpha variant," researchers from Public Health England and the University of Cambridge wrote in their new study.

"Emergency care attendance combined with hospital admission was also higher for patients with the Delta variant, showing increased use of emergency care services as well as inpatient hospitalization," the researchers wrote.

'Getting fully vaccinated is crucial'

The study included data on 8,682 Covid-19 patients in England who were infected with the Delta variant and 34,656 infected with the Alpha variant. Across both groups, most of the patients -- 74% -- were unvaccinated.

The patients were tested for Covid-19 between March 29 and May 23 of this year, and the researchers examined how many of them were hospitalized.

In general, 2.3% of patients with Delta and 2.2% of patients with Alpha were admitted to the hospital within two weeks after they were tested for Covid-19.

But once the researchers accounted for certain factors that could raise a patient's risk for hospitalization, such as age or vaccination status, they found Delta was associated with a 2.26-fold increased risk of hospitalization compared with Alpha and 1.45-fold increased risk of requiring emergency care or hospital admission.

The researchers noted that their study results are similar to separate research previously conducted in Scotland that also found a higher risk of hospital admission within 14 days for patients infected with Delta versus Alpha.

"Our analysis highlights that in the absence of vaccination, any Delta outbreaks will impose a greater burden on healthcare than an Alpha epidemic," Dr.

Anne Presanis, one of the study's lead authors and senior statistician at the University of Cambridge, said in a news release Friday.

"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," Presanis said.

'This is not a surprise'

Some doctors and scientists not involved in the new study have said that the findings confirm what was already thought -- that the Delta variant is more likely to cause serious disease.

"These data confirm what we are seeing in clinical practice, namely that, 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," Dr. David Strain, senior clinical lecturer at the University of Exeter who was not involved in the study, said in a written statement distributed by the UK-based Science Media Centre.

"It highlights the need for a comprehensive vaccine program in younger adults and it clearly demonstrates the preconception that they do not get severe
Covid is no longer true," Strain said. "This is not a surprise, as the two things that make the Delta variant more infectious will also have a role in the disease severity."

The researchers also noted in their study that new Covid-19 infections in England have been increasingly caused by the Delta variant. Although the proportion of cases in the study caused by the Delta variant was 20% overall, the researchers wrote, "this increased to 74% of new sequenced cases in the week starting May 31, 2021."

During this summer in the United States, the Delta variant overtook the Alpha variant, first identified in the United Kingdom, as the dominant coronavirus strain circulating.

"The Delta variant was responsible for the uptick in Covid cases this summer in the UK, and many of us have heard of even vaccinated people that became infected," Dr. Zania Stamataki, viral immunologist at the University of Birmingham who was not involved in the new study, said in a separate statement from the Science Media Centre.

"The new study "measures hospitalizations as a surrogate marker of severe disease, and the findings are clear: the Delta variant increases hospitalizations compared to the Alpha variant previously prevalent in the UK," Stamataki said. "Taken together with previous studies showing that Delta is 50% more infectious than Alpha, evidence mounts that we are dealing with a very dangerous variant. Both vaccine doses are needed for maximum protection."