Former CDC Director Robert Redfield suggested that a bird flu pandemic among humans is inevitable and would be extremely lethal. (Watch the video below.)

Redfield, who headed the Centers for Disease Control and Prevention from 2018 to 2021 after being appointed by the Trump administration, gave an alarming interview to NewsNation on Friday after the World Health Organization announced the bird-flu-related death of a 59-year-old man in Mexico.

I really do think its very likely that we will, at some time its not a question of if, its more of a question of when we will have a bird flu pandemic, Redfield said.

A wide variety of mammals have been found harboring the virus including cows , cats, ferrets and elephant seals. The odds are increasing of a scourge between humans that could kill 25 to 50 percent of those it infects, Redfield warned.

The overall case-fatality rate for COVID-19 before vaccines were available was 1.7%, according to CDC stats .

Redfield said scientists have found that the bird flu virus hasnt yet adapted to spread from humans to humans, but that once it does, thats when youre going to have the pandemic, The Hill reported . And as I said, I think its just a matter of time.

Another expert expressed similar concern. Are we watching the beginning? Is this where were seeing repeated spillovers that one day take off? Or is it like in COVID, where suddenly theres a cluster of human cases and then its too late? Louise Moncla, an avian flu researcher and assistant professor at the University of Pennsylvania, told the CBC .

The World Health Organization reported earlier this month that the 59-year-old man in Mexico, who had comorbidities and died from the virus in late April, had no known contact with poultry or other animals.

The strain he had, called H5N2, had never been found in humans before, The Associated Press reported .

The bird flu strain currently affecting dairy cattle, H5N1, has reportedly given three U.S. farmworkers mild symptoms. Since its discovery in 1996, however, H5N1 has infected some 900 people around the world, with a mortality rate of about 50 percent.

The risk here of something going from one or two sporadic cases to becoming something of international concern, its not insignificant, CDC Principal Deputy Director Nirav Shah told Politico in May. Weve all seen how a virus can spread around the globe before public health has even had a chance to get its shoes on. Thats a risk and one that we have to be mindful of.

According to a CDC timeline of avian influenza outbreaks , 36 people in China were diagnosed with HPAI H5N6 in 2021, and 18 of them died. Bird flu usually spreads among birds and other animals, but can infect humans exposed to an animals body excretions, like spit or feces.