A large U.K. study released Friday found that people with Omicron infection are more likely to need hospital treatment than those who have had Delta.

Latest data from the U.K. Health Security Agency shows that the chance of hospitalization infected by omicron was about three times as high than for those with the delta variant. From Nov. 22 to Dec. 26, in England, the study examined more than 528,000 cases of omicron and 573,000.

Susan Hopkins, the Chief Medical Advisor cautioned however that it was still premature to make definitive judgments about the severity and extent of omicron-related illness.

Hopkins stated that “the increased transmission of omicron, and the increasing cases in over-60s in England mean it remains highly probable that there will be significant stress on the NHS in the coming weeks”, referring to U.K.’s National Health Service.

On Wednesday, the World Health Organization warned that it was too soon to say that omicron has a milder effect than previous Covid types. According to Dr. Abdi Mahamud (WHO’s incident manager for Covid), omicron is more common in younger individuals who are less likely to develop severe illness.

We all wish this disease would be less severe, however the majority of those it has affected are younger. How it behaves in the elderly population, the vulnerable — we don’t know yet,” Mahamud said during a news briefing in Geneva.

A new U.K. study found that Covid vaccines decrease the likelihood of being hospitalized from omicron in all age groups. However, a booster dose offers the greatest protection. This latest evidence adds to the growing amount of data proving that vaccines still offer significant protection, even if they have suffered a decrease in omicron.

The study found that one dose of vaccine is effective for preventing hospitalizations from the Omicron variant at 52%, and two doses are effective at 72%. The two vaccine doses were only 52% and 52% respectively effective in preventing hospitalization after 25 weeks.

The study concluded that booster doses dramatically increase the protection of the patient and 88% prevent hospitalization within two weeks.

According to the U.K. Health Security Agency, “Protection from hospitalization is good against the Omicron variant.”

According to the FDA, current vaccines have less effectiveness in protecting against symptomatic infection due to omicron as compared with the Delta variant. AstraZeneca’s vaccine is available in the U.K. and not the U.S. It does not protect against symptoms of omicron infection 20 weeks following the first dose.

Moderna and Pfizer’s vaccines are the most commonly administered shot in America. However, only 10% of them prevent symptomatic infection 20 weeks following the first dose. The booster doses provide greater protection, and up to 75% effectiveness in preventing infection after two to four weeks. The study found that boosters lose effectiveness after 10 weeks and provide 40 to 50% protection from symptomatic infections.

Sajid Javid, U.K. Health Secretary, stated that the non-vaccinated are eight to one more likely than those who have been vaccinated.