Although the highly contagious Omicron variant appears to be less severe than the Delta variant, it shouldn’t be categorized as “mild,” the WHO said on Thursday.

“Just like previous variants, Omicron is hospitalizing people and it is killing people,” Tedros Adhanom Ghebreyesus, the director-general of the WHO, said during a COVID-19 news briefing.

“In fact, the tsunami of cases is so huge and quick, that it is overwhelming health systems around the world,” he said.

Hospitals are becoming overcrowded and understaffed, which leads to deaths not only from COVID-19 but also other diseases and injuries where patients can’t receive timely care, he said.

The highest number of worldwide COVID-19 cases was reported last week, he said, adding that the WHO knows “for certain” that the count was an underestimate.

“Reported numbers do not reflect the backlog of testing around the holidays, the number of positive self-tests not registered, and burdened surveillance systems that miss cases around the world,” he said.

So far, fewer patients need to be hospitalized due to the Omicron variant, but with the large number of people contracting COVID-19, hospitalization numbers are increasing. At Northwell Health in New York, about 10% of patients are ending up in intensive care, as compared with 25% to 35% in previous surges, according to The Wall Street Journal. Fully vaccinated patients are staying for an average of four days, and unvaccinated patients are staying for almost two weeks.

WHO officials encouraged global leaders to support campaigns to vaccinate 70% of people in every country by the middle of 2022 and ensure that reliable tests and breakthrough treatments are available in all countries. At the current pace of vaccine rollouts, 109 countries would miss the goal of fully vaccinating 70% of their populations by the beginning of July.

“Vaccine inequity is a killer of people and jobs, and it undermines a global economic recovery,” Tedros said. “Alpha, Beta, Delta, Gamma and Omicron reflect that in part because of low vaccination rates, we’ve created the perfect conditions for the emergence of virus variants.”

Some countries are beginning to vaccinate people with a fourth dose while others haven’t received enough regular supply to fully vaccinate their health care workers and most vulnerable groups, he added. In fact, 36 countries haven’t reached the 10% vaccination mark, and among the most severe patients worldwide, 80% are unvaccinated.

“Booster after booster in a small number of countries will not end a pandemic while billions remain completely unprotected,” he said.

Speculations that the Omicron variant might be the last outbreak of the pandemic are “wishful thinking,” Michael Ryan, MD, the WHO emergencies chief, told reporters during the briefing.

“There still is a lot of energy in this virus,” he said.

Maria Van Kerkhove, the WHO’s technical lead on COVID-19, backed up Ryan’s thoughts.

“I think it’s very unlikely that Omicron will be the last variant that you will hear us discussing,” she said.