The risk of hospitalization is probably about twice as high for infection with the delta variant of the coronavirus as for the alpha variant, according to a study. Researchers from the University of Cambridge and Public Health England evaluated more than 40,000 corona cases in England between the end of March and the end of May 2021 for their study. The findings, published in the journal Lancet Infectious Diseases, can be related primarily to risk for the unvaccinated. For fully vaccinated people, the data do not allow any conclusions.

Until now, studies had mainly demonstrated the higher transmissibility of the delta variant; there were hardly any reliable statements about the risk of severe courses. The scientists now used the results of tens of thousands of positive tests that had been assigned to delta or alpha via genetic analyses. Accordingly, almost 9,000 were due to delta, and around 35,000 to alpha. In relation to this, the researchers looked at the number of hospital admissions.

After adjusting the data for factors such as age and demographic characteristics that typically favor the risk of serious illness, they found a mean 2.26-fold higher risk of hospitalization within two weeks of testing for infection with delta. Accordingly, the risk of needing to visit an emergency room or be hospitalized within 14 days was 1.45-fold higher with delta than with alpha.

Among the more than 40,000 cases examined in the study, only 1.8 percent were fully vaccinated, which the researchers interpret as renewed confirmation that the vaccines are very effective in protecting people. Seventy-four percent of the infected people considered were unvaccinated, and 24 percent were only partially vaccinated, meaning they had received about only one dose of vaccine. Because of the paucity of data available for this purpose, the researchers cannot make any conclusions about whether a higher risk of severe disease is also present in those who have been vaccinated.

"Our evaluation shows that delta outbreaks without vaccination are a significantly greater burden on the health care system than an alpha epidemic," said one of the study authors, Anne Presanis of the University of Cambridge. "Getting fully vaccinated is critical to reducing one's risk of symptomatic infection and reducing the risk of becoming severely ill and hospitalized from a delta infection."The authors cite as weaknesses in their study that they did not have data on their patients' pre-existing conditions. Also, they say, it's possible that the rules for hospitalizations changed during the trial period. The researchers at least tried to minimize these factors in their calculations.

Photo by Olga Kononenko