The unlikely prospect of a COVID-19 variant that outsmarts vaccines 'keeps me up at night,' CDC Director Rochelle Walensky says in The EIC Interview

• CDC Director Rochelle Walensky said the coronavirus was not done mutating.
• She told Insider's global EIC the idea of a variant that evades vaccine immunity kept her up.
• Many experts told Insider it was unlikely the virus could completely outsmart our immune systems.

Rochelle Walensky, the director of the Centers for Disease Control and Prevention, fears the unlikely possibility that a future COVID-19 variant could evade vaccines completely, she told Insider Global Editor in Chief Nicholas Carlson in The EIC Interview.

Viruses mutate to survive as they move from person to person. The unvaccinated population in the US is a breeding ground for variants, some of which have been known to spread among vaccinated people.

Mutations to the coronavirus already brought about the Delta variant, which is driving a surge in cases just when it seemed we might be out of the woods.

"What we saw with Delta is that it mutated in a way that led to increased transmission," Walensky said. "If you have increased transmission in the context of a lot of people vaccinated, the next potential way for it to mutate is to mutate to some benefit to outdo the vaccination."

She added: "When people ask the question, 'What keeps you up at night?' - those are the things that keep me up at night."

Many experts say it's unlikely a variant could outsmart our vaccines anytime soon

Stanley Perlman, a microbiologist who has been studying coronaviruses for more than 30 years, told Insider the likelihood of a "terrible possibility," like a variant that completely evades existing vaccines, was low.

The variants we've seen dominate so far - Alpha and now Delta - have been more transmissible compared with their predecessors. But, Perlman said, a highly infectious variant is typically less deadly, since it must sacrifice its strengths to fly under the radar of the immune system.

Paul Offit, a coinventor of the rotavirus vaccine, told Insider it was not a given that the virus would eventually mutate away from vaccine-induced immunity. Measles, which is an RNA virus, like the novel coronavirus, has been coexisting with the vaccine for almost 60 years, he said. While the virus continues to mutate, it hasn't mutated away from the vaccine.

"In terms of virulence, it's never really to the advantage of the virus to be more virulent, to kill you. It really needs you to continue to reproduce itself," Offit said.

Like variants, our vaccine-fortified immune systems have many tricks up their sleeves, Tyler Starr, an evolutionary biologist who has been mapping all possible mutations to a key protein in the novel coronavirus, told The New Yorker's Dhruv Khullar. The COVID-19 vaccines generate a multifaceted antibody response, so "when one set of antibodies drops the rope, another will pick it up," Starr added.

For example, a study published in Nature in July found Delta evaded antibodies but not the entire immune system. Two doses of the AstraZeneca or Pfizer vaccine successfully neutralized the Delta variant in 95% of people, even though antibody levels were three to five times lower compared with the response to the Alpha variant.

Perhaps that's why the vaccines have worked pretty well in the face of variants we've seen so far, continuing to prevent severe disease and death.

Offering the coronavirus an opportunity to spread gives vaccine developers more work and prolongs the pandemic

Evolving to become more contagious means the virus can infect more people. The more people it infects, the greater chance it has to mutate further.

Walensky told Insider that was not a good situation to be in, even with the vaccines working as well as they do.

"The more replication that happens, the more likely it will mutate to some advantage of the virus," Walensky said.

"Now, will the next advantage to the virus be that it'll outdo our vaccines? I don't know," she added. "Will it be some other way that it can outsmart us? I don't know, but I guess what I'm saying is: When these mutations take hold, they generally do so to some benefit of the virus, and if it's to a benefit of the virus, it's to a detriment of us.

"That's what I'm trying to prevent."