GENEVA, Nov. 28 (Xinhua) -- Modeling studies under certain conditions show that about 60 to 70 percent of the population need to be immune to curb or halt COVID-19 transmission, a World Health Organization (WHO) official said Friday.

Noting the WHO cannot give the exact number of "the proportion of the population that would need to be immunized," Katherine O'Brien, director of WHO's Department of Immunization, Vaccines and Biologicals, said during a virtual briefing that "the answer to that can come from modeling studies."

"These modeling studies ... under a variety of conditions have concluded that somewhere around 60 to 70 percent of the population would need to be immune, presumably through immunization, in order to achieve a reduction or an interruption of transmission of the virus," she said.

"That's of course predicated on what the performance of the vaccines would be," she added.

Global COVID-19 cases have surpassed 61 million with the death toll topping 1.4 million, according to the latest data from Johns Hopkins University.