Delta Variant Doubles Hospitalization Risk

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People who contract the Delta variant have double the risk of hospitalization, as compared with earlier versions of the coronavirus, according to a new study published Friday in The Lancet Infectious Diseases.

Based in England, the large study found that the Delta variant led to a higher rate of hospital admission and emergency care, with fewer than 2% of infections occurring in fully vaccinated people.

“The main takeaway is that if you have an unvaccinated or only partially vaccinated population, then an outbreak of Delta can lead to a higher burden on hospitals, on health care, than an Alpha outbreak would,” Anne Presanis, one of the lead study authors and a biostatistician at the University of Cambridge, told The New York Times .

Presanis and colleagues analyzed health data for more than 43,000 people who were infected with COVID-19 between March 29 and May 23. Among the people in the study, 74% were unvaccinated, 24% were partly vaccinated, and 2% were fully vaccinated.

At that time, 80% were infected with the Alpha variant, also known as B.1.1.7, and 20% were infected with the Delta variant, or B.1.617.2. Those infected with Delta were younger, on average.

The risk of hospitalization was small for both groups — about 2.2% of those with the Alpha variant and 2.3% of those with the Delta variant were admitted to a hospital within 2 weeks of testing positive.

But once the researchers accounted for things that raise a patient’s risk for hospitalization, they found Delta was linked to more than twice a higher risk, particularly for those who were unvaccinated or only partially vaccinated.

“We already know that vaccination offers excellent protection against Delta,” Gavin Dabrera, a lead author and an epidemiologist at Public Health England, said in a statement.

“As this variant accounts for over 98% of COVID-19 cases in the U.K., it is vital that those who have not received two doses of vaccine do so as soon as possible,” he said.

The Delta variant accounts for nearly 99% of new COVID-19 cases in the U.S., according to NBC News. Public health officials have known for months that the Delta variant is more contagious than previous versions of the coronavirus, but it’s been unclear whether it leads to more severe disease and hospitalization.

“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,” David Strain, a senior clinical lecturer at the University of Exeter, told the Science Media Centre.

“It highlights the need for a comprehensive vaccine program in younger adults,” he said. “And it clearly demonstrates the preconception that they do not get severe COVID is no longer true.”


The Lancet Infectious Diseases: “Hospital admission and emergency care attendance risk for SARS-CoV-2 delta (B.1.617.2) compared with alpha (B.1.1.7) variants of concern: a cohort study.”

The New York Times: “The Delta variant carries a higher risk of hospitalization, a study finds.”

EurekAlert: “The Lancet Infectious Diseases: Delta variant doubles risk of COVID-19 hospitalisation compared to alpha variant, new UK study confirms.”

NBC News: “Delta variant doubles the risk of hospitalization, study confirms.”

Science Media Centre: “Expert reaction to study looking at risk of hospitalization from the delta variant compared with alpha.”

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