People who get COVID-19 from the Omicron virus variant are less likely to require hospital care, according to a UK study published Wednesday.
Researchers from the Imperial College London estimated (pdf) that Omicron patients were 20- to 25-percent less likely to need hospital care and 40- to 45-percent less likely to be hospitalized for one night or more when compared to patients with the Delta variant.
They arrived at the estimates by analyzing data from all COVID-19 cases in England between Dec. 1 and Dec. 14, as determined by a positive polymerase chain reaction test.
The researchers also estimated that natural immunity, or protection from a prior infection, reduces the risk of hospitalization by 50 percent and the risk of a hospital stay of one night or more by 61 percent. People vaccinated with the Pfizer or Moderna vaccines, meanwhile, had a similar or higher risk for hospitalization with the new strain, while people who got AstraZeneca’s vaccine had a lower risk.
Limitations of the study include the short time period studied and a lack of data on reported reasons for hospitalizations, which in some cases may be unrelated to COVID-19.
“Our analysis shows evidence of a moderate reduction in the risk of hospitalization associated with the Omicron variant compared with the Delta variant. However, this appears to be offset by the reduced efficacy of vaccines against infection with the Omicron variant,” professor Neil Ferguson, who led the study, said in a statement.
Authors received funding from several institutions, including the UK’s National Institute for Health Research.
Omicron was first identified in South Africa last month and dates back to at least November. Omicron and Delta are both variants of the CCP (Chinese Communist Party) virus, which causes COVID-19.
The UK analysis provides further evidence of Omicron causing less severe cases of COVID-19; South Africa has recorded a major drop in hospitalization rate during the Omicron-fueled wave compared to the wave powered by infections caused by Delta.
A preprint study performed by researchers in the country and published earlier Wednesday pegged the odds of requiring hospitalization at 80 percent lower for people with Omicron when compared to others.
Additionally, people who got Omicron and went to a hospital were 70 percent less likely to develop severe disease.
Experts say the high level of natural immunity in South Africa may play a role in the reduced severity, and have questioned whether the same pattern would be seen in other countries.
A large proportion of England’s population has been infected by COVID-19.
Nearly 10 million people, or 17 percent of the population, had tested positive for the illness as of Dec. 21. Based on several studies, the Imperial College London researchers believe fewer than a third of infected people were tested, and estimate over half of the population has survived infection.
In that context, the finding that natural immunity dramatically reduced the risk of hospitalization “is significant,” they said.
World Health Organization officials said Wednesday that early data point to Omicron being both more transmissible and less severe than earlier strains but cautioned against drawing conclusions too soon.
“We don’t have that complete picture yet,” Dr. Maria van Kerkhove, WHO’s technical lead on COVID-19, told a briefing. “We have not seen this variant circulate for long enough in populations around the world, certainly in vulnerable populations.”
Multiple factors are likely behind the increased transmissibility seen in several countries, including Omicron having more mutations and being able to better evade immunity from prior infection and vaccination, she added.