“We observed unprecedented levels of infection with SARS-CoV-2 in England in January 2022 and almost complete replacement of Delta by Omicron,” the report authors said Wednesday. The U.K. has reported between 70,000 and 150,000 cases per day throughout January.

But not only is Omicron now dominant—not just in England, but in most countries where it exists—the highly virulent variant is also reinfecting people who were previously infected by other strains of COVID-19.

According to the report, 64.6% of recorded cases in England were found in people who proved they had had a previous COVID infection. A further 7.5% of those with positive cases said they suspected they had suffered COVID before, although had not been tested for the disease. The report pours cold water on theories that prior infection might help guard against reinfection from Omicron.

“Vaccination remains the best way to protect yourself from severe disease and hospitalization from Omicron, and I would urge anyone who has not done so to come forward for their first, second, and third doses as soon as possible,” Jenny Harries, chief executive of the U.K. Health Security Agency said.

According to the U.K. government, health authorities have distributed over 37 million booster shots since the start of January. With the vaccination rate high and COVID case numbers receding, the U.K. will lift most of its current COVID restrictions on Thursday.

Face masks will no longer be mandatory inside public venues, although they are still recommended, and venues such as bars and restaurants will no longer require proof of vaccination for entry. But the government continues to advise caution.

“COVID-19 rates are still high, so as we learn to live with the virus it is vital we continue to be vigilant,” U.K. Health Secretary Sajid Javid said Wednesday. “Wash your hands, let in fresh air, get tested, and if you haven’t already, get boosted now.”