Past experiences indicated that a COVID-19 surge may appear in the southern United States this summer, former White House coronavirus response coordinator Dr. Deborah Birx said Sunday.

"We should be preparing right now for a potential surge in the summer across the southern United States because we saw it in 2020 and we saw it in 2021," Birx said in an interview on CBS' "Face the Nation."

The country experienced "predictable" surges across the south during summer as well as in the winter. The winter surge starts in the northern plains and moves down, accelerated by Thanksgiving and the Christmas, Kwanzaa and Hanukkah holidays, the doctor said.

Birx forecasted the country's summer surge following her observations on South Africa, which is currently experiencing what local health officials and scientists claimed was a fifth wave of COVID-19 infections caused by omicron's BA.4 and BA.5 sub-variants.

“[South Africa is] good about testing. They're good about sequencing and [finding] their variants. ... Each of these surges are about four to six months apart. That tells me natural immunity wanes enough in the general population after four to six months that a significant surge is going to occur again," Birx explained.

The surges were caused by vaccine protection waning as well as the appearance of "slightly different" COVID-19 variants, according to the doctor.

Birx's remarks come as billionaire and philanthropist Bill Gates suggested that the world may have not seen the "worst" of the pandemic yet.

"[I]t’s way above a [5%] risk that this pandemic, we haven’t even seen the worst of it," the co-founder and former head of tech giant Microsoft said.

He added that a more transmissive and fatal coronavirus variant could still appear in the future.

The Centers for Disease Control and Prevention (CDC) maintains that getting vaccinated "is the best way to slow down the spread of SARS-CoV-2, the virus that causes COVID-19."

These vaccines "are effective at preventing you from getting sick" and are "highly effective at preventing severe illness, hospitalizations and death," according to the health agency.

The U.S. has reported a total of 81,173,065 COVID-19 cases and 991,030 virus-related deaths since the start of the pandemic, data provided by the CDC showed.