“There is no world, I think, where [the effectiveness] is the same level…we had with [the] Delta [variant],” Stéphane Bancel told the Financial Times in an interview published Tuesday. “I think it’s going to be a material drop. I just don’t know how much because we need to wait for the data. But all the scientists I’ve talked to…are like, ‘This is not going to be good.’”

Bancel says the new variant has particular mutations around the spike protein, which helps a virus enter a host cell. Current vaccines focus on that spike protein, and that’s why the mutations could make them less effective.  

The World Health Organization considers Omicron a “variant of concern,” the virus evolution advisory group’s COVID-19 technical lead, Dr. Maria Van Kerkhove, said in a public statement on Friday. Based on initial research, Rockefeller University virologist Paul Bieniasz told NPR that he and his colleagues “expect that Omicron will be significantly resistant to antibodies that are circulating in individuals who are convalescent or who have had mRNA vaccines.” 

However, Bienasz said his research does show that three vaccine shots, or one infection paired with two vaccine doses, can enhance immunity against Omicron.  

Scientists say it’s too early to tell whether Omicron is actually more infectious than other variants. Dr. Angelique Coetzee, national chair of the South African Medical Association, said on Tuesday that Omicron is not yet cause for extreme concern. 

“The majority of what we are presenting to primary health care practitioners are extremely mild cases,” she said.