Top epidemiologist: Delta variant is 'maybe the most contagious virus' ever

A top epidemiologist is warning that the highly transmissible delta variant of COVID-19 might be one of the most contagious diseases in recent history.

"This is maybe the most contagious virus that we've ever seen in living memory," Larry Brilliant, who worked with the World Health Organization to help eradicate smallpox, said in an interview with CNBC on Friday.

Brilliant, who is the founder and CEO of Pandefense Advisory, said it feels like the world is still dealing with the beginning of the pandemic rather than the end due to the new variant.

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Brilliant went on to say that new strains of the coronavirus will develop unless vaccinations increase globally.

“Unless we vaccinate everyone in 200-plus countries, there will still be new variants,” he said.

Brilliant’s remarks come amid a surge in COVID-19 cases in the U.S. from the delta variant, with unvaccinated people being the hardest hit.

Brilliant encouraged people who are 65 or older to get booster shots in the near future, saying that their weak immune system may cause them to be more vulnerable to the virus.

“So those people, I would say, should be given a third dose, a booster right away — as quickly as moving the vaccines to those countries that haven’t had a very high chance to buy them or have access to them,” Brilliant said. “I consider those two things about equal.”

The debate over whether to administer booster shots is heating up as some public health experts warn countries against moving forward with plans to offer third doses at a time when millions of people have not even received their first dose.