Omicron Hospitalization Risk 80 Percent Less Than Delta—South Africa Study

South Africans contracting the Omicron variant are 80 percent less likely to be hospitalized with the disease than if they had caught another COVID strain, a new study by the country's National Institute of Communicable Diseases (NICD) has revealed.

The study, which collected the data of thousands of COVID cases through November, found that once Omicron patients were admitted to hospital, the risk of severe disease didn't differ from other variants.

The scientists who authored the study said that some of the reduction was probably due to South Africa's high population immunity. According to antibody surveys, between 60 and 70 percent of people in the African country may have been infected by COVID previously. The percentage of South Africans who were vaccinated was also higher than it was during the Delta wave.

In the study, those with Omicron infections were associated with 70 percent lower odds of severe disease compared those with Delta infections.

The research also found that those with Omicron may have higher viral loads.

The scientists adjusted confounding variables that could influence the results, including age, gender, hospital bed availability and whether there were known reinfections. They also adjusted for the presence of other illnesses and prior immunization to gauge the severity of disease after admission.

"All of these decreased admission/severity results could be explained by a combination of pre-existing immunity (from natural infection or vaccination) and decreased virulence of the virus," Dr. Anne von Gottberg, one of the study authors, told Newsweek.

But the authors recognized several limitations to the study, including the number of Omicron infections being underestimated and biased towards geographic regions where the type of PCR test they used to detect the new variant was more commonly used.

The NICD said that among patients that had a known hospital outcome, 32 percent of COVID admissions during the early fourth wave were severe compared to 65 percent during the early third wave, when the Delta variant was dominant.

"It is difficult to disentangle the relative contribution of high levels of previous population immunity versus intrinsic lower virulence to the observed lower disease severity. Our finding of no difference in severity in SGTF [Omicron] compared to non-SGTF infected individuals in the same time period, and the lower risk of severity in SGTF compared to earlier Delta infected individuals, suggests that this reduced severity may be in part a result of high levels of population immunity (due to natural infection and/or vaccination)," the paper said.

The Omicron variant quickly rose to prominence in South Africa, especially in the Gauteng province, home to Johannesburg, the country's most populous city. At the beginning of the fourth wave at the end of November and beginning of December, South Africa's COVID infections were doubling each day.

However, the last three days have seen a fall in new cases, indicating that the fourth wave may have peaked. On Tuesday, South Africa's seven-day average number of daily infections was 18,195. On December 17, this average was at its highest, at 23,384 infections, according to Our World In Data. But deaths have been climbing – with the seven-day daily average being 45 on Tuesday, compared to 31 on December 17, at the peak of infections.

Omicron peak quicker SA
A patient gets vaccinated by the Witkoppen clinic at the Kya Sands informal settlement in Johannesburg on December 8, 2021. South Africans contracting the Omicron variant are 80 percent less likely to be hospitalized with the disease than if they had caught another strain, a new study by the country’s National Institute of Communicable Diseases (NICD) has revealed. Emmanuel Croset/Getty

Update, 12/23/21 4.10 a.m. ET: This article was updated to include comments from the authors of the research paper.