CNN  — 

Two new preprint papers add to the growing evidence that the Omicron coronavirus variant may be less likely to cause severe disease and hospitalization compared to the Delta variant.

Omicron is associated with a two-thirds reduction in the risk of Covid-19 hospitalization compared with Delta, suggests one study, released online Wednesday as a working paper by researchers at the University of Edinburgh in the United Kingdom. That research was based out of Scotland.

The other paper, posted Tuesday to the online server, suggests that people with Omicron infections have had 80% lower odds of being admitted to the hospital compared with Delta infections. But once a patient was hospitalized, there was no difference in the risk of severe disease, according to that research, based out of South Africa.

Both studies include preliminary data and have not yet been published in a peer-reviewed journal.

The study out of Scotland included data on 23,840 Omicron cases and 126,511 Delta cases, from November 1 to December 19. The researchers – from the University of Edinburgh, University of Strathclyde and Public Health Scotland – took a close look at the health outcomes among those Omicron infections compared with Delta infections. There were 15 hospital admissions among those with Omicron infections and 856 hospital admissions among Delta.

“Although small in number, the study is good news. The two thirds reduction in hospitalisation of double vaccinated young people compared to Delta indicates that Omicron will be milder for more people,” James Naismith, director of the Rosalind Franklin Institute and professor of structural biology at the University of Oxford, who was not involved in either study, said in a written statement distributed by the UK-based Science Media Centre on Wednesday.

“The study is rigorous but it is early (thus might change a bit with more data and more studies will report in the weeks ahead). It should be noted that some South African scientists have been saying Omicron was milder for some time,” Naismith said. “Although two thirds reduction is significant, Omicron can cause severe illness in the doubly vaccinated. Thus, if Omicron continues to double every few days, it could generate many more hospitalisations than Delta from the double vaccinated population.”

The researchers found that the proportion of Omicron cases that were likely reinfections in people who have had Covid-19 before was more than 10 times that of Delta. The data also showed that having received a third dose of vaccine, or booster shot, was associated with a 57% reduction in the risk of symptomatic Omicron infection when compared with being at least 25 weeks out from completing a second dose.

“These early national data suggest that Omicron is associated with a two-thirds reduction in the risk of COVID-19 hospitalisation when compared to Delta. Whilst offering the greatest protection against Delta, the third/booster dose of vaccination offers substantial additional protection against the risk of symptomatic COVID-19 for Omicron,” the researchers wrote in the paper.

The other paper involved data on 161,328 Covid-19 cases reported nationally in South Africa between October 1 and December 6. The researchers – from the National Institute for Communicable Diseases, University of the Witwatersrand and the University of Cape Town – found that among people with Omicron infection, 2.5% were admitted to the hospital during that time compared with 12.8% of people with Delta infection.