People infected with the highly contagious Delta variant are twice as likely to be hospitalized as people infected with the Alpha variant, according to a large new UK study.
The study, published on Friday in The Lancet Infectious Diseases, is an analysis of more than 40,000 coronavirus infections in England. It adds to the evidence suggesting that Delta can cause more severe illness than other variants.
Less than 2 percent of infections occurred in people who were fully vaccinated, and there wasn’t enough data to draw concrete conclusions about hospitalization risks specifically in this group, the researchers said.
“The key finding is that in an unvaccinated or partially vaccinated population, a delta outbreak can place greater stress on hospitals and health care than an alpha outbreak,” said Anne Presanis, a senior statistician at the University of Cambridge and one of the lead authors of the study.
The Delta variant, first discovered in India, is about twice as contagious as the original virus and up to 60 percent more transmissible than the Alpha variant first identified in Great Britain.
In the new study, researchers analyzed health records from people who tested positive for the virus in England between March 29 and May 23, while Delta spread across the country. 74 percent of people were unvaccinated, 24.2 percent partially vaccinated and 1.8 percent fully vaccinated.
Genetic sequencing confirmed that 80 percent of study participants were infected with the alpha variant, while 20 percent were infected with delta.
For both groups, the risk of hospitalization was low, the researchers found. Only 2.2 percent of people with alpha and 2.3 percent of people with delta were hospitalized within two weeks of testing positive for the virus.
But the people who infected the Delta variant were younger on average. When the researchers corrected age and other factors known to affect disease severity, they found that the overall risk of hospitalization was more than double what Delta caused the infection .
When the researchers broken down the data by vaccination status, they confirmed that Delta doubled the risk of hospitalization for those who weren’t vaccinated or who had received their first dose less than three weeks earlier. The fully vaccinated group was too small to be rigorously analyzed alone, the researchers said.
“We already know that vaccination offers excellent protection against Delta, and with this variant accounting for over 98 percent of Covid-19 cases in the UK, it is important that those who have not received two doses of the vaccine do so as soon as possible possible do. “Said Dr. Gavin Dabrera, a lead author on the paper and an epidemiologist with Public Health England, in a statement.