Cases of the Omicron variant now account for 73% of COVID infections in the U.S., the CDC said Monday, and it has taken over from Delta as the dominant strain. People around the world are contracting the virus at fast-increasing rates. But the tweets from Gates, the cofounder of Microsoft, bore particular weight because he has studied infectious disease and has advocated for wider vaccination as part of his philanthropic work over the past 20 years.

Gates said in a tweet that “we could be entering the worst part of the pandemic” and that “Omicron will hit home for all of us.” The billionaire said some of his close friends have been infected with the virus and that he has already canceled most of his holiday plans. Gates warned that there will continue to be more breakthrough infections among vaccinated people—not because COVID vaccines don’t work, but because the new variant is more infectious than those that came before it.

Because of its apparent resistance to vaccines, the Omicron variant is spreading rapidly even in areas where the population has a high level of immunity, according to the World Health Organization. 

Even though early research from South Africa suggests that those infected with the Omicron variant are 80% less likely to be hospitalized than those hit by earlier strains, its increased infectiousness is putting the immunocompromised at risk worldwide.

Gates ended his Tweet thread on a positive note. He said that once Omicron becomes the dominant variant in a country, that country’s infection wave could be over in less than three months. Gates wrote that he believes the pandemic could still end in 2022.

In the meantime, Gates said people need to take proper precautions including wearing masks, avoiding big indoor gatherings, and getting the COVID vaccine or booster.

“Someday the pandemic will end, and the better we look after each other, the sooner that time will come,” Gates concluded.