July 30, 2021 -- The CDC Director Rochelle Walensky, MD, made a dire prediction during a media briefing this week that, if we weren't already living within the reality of the COVID-19 pandemic, would sound more like a pitch for a movie about a dystopian future.

"For the amount of virus circulating in this country right now largely among unvaccinated people, the largest concern that we in public health and science are worried about is that the virus…[becomes] a very transmissible virus that has the potential to evade our vaccines in terms of how it protects us from severe disease and death," Walensky told reporters on Tuesday.

A new, more elusive variant could be "just a few mutations away," she said.

"That's a very prescient comment," Lewis Nelson, MD, professor and clinical chair of emergency medicine and chief of the Division of Medical Toxicology at Rutgers New Jersey Medical School in Newark, tells Medscape Medical News.

"We've gone through a few mutations already that have been named, and each one of them gets a little more transmissible," he says. "That's normal, natural selection and what you would expect to happen as viruses mutate from one strain to another."

"What we've mostly seen this virus do is evolve to become more infectious," says Stuart Ray, MD. "That is the remarkable feature of Delta — that it is so infectious."

He says that the SARS-CoV-2 has evolved largely as expected, at least so far. "The potential for this virus to mutate has been something that has been a concern from early on."

"The viral evolution is a bit like a ticking clock. The more we allow infections to occur, the more likely changes will occur. When we have lots of people infected, we give more chances to the virus to diversify and then adapt to selective pressures," says Ray, vice-chair of medicine for data integrity and analytics and professor in the Division of Infectious Diseases at Johns Hopkins School of Medicine in Baltimore, Maryland.

"The problem is if the virus changes in such a way that the spike protein — which the antibodies from the vaccine are directed against — are no longer effective at binding and destroying the virus, and the virus escapes immune surveillance," Nelson says.

If this occurs, he says, "we will have an ineffective vaccine, essentially. And we'll be back to where we were last March with a brand-new disease."

Technology to the Rescue?

The flexibility of mRNA vaccines is one potential solution. These vaccines could be more easily and quickly adapted to respond to a new, more vaccine-elusive variant.

"That's absolutely reassuring," Nelson says. For example, if a mutation changes the spike protein and vaccines no longer recognize it, a manufacturer could identify the new protein and incorporate that in a new mRNA vaccine.

"The problem is that some people are not taking the current vaccine," he adds. "I'm not sure what is going to make them take the next vaccine."

Nothing Appears Certain

When asked how likely a new strain of SARS-CoV-2 could emerge that gets around vaccine protection, Nelson says, "I think [what] we've learned so far there is no way to predict anything" about this pandemic.

"The best way to prevent the virus from mutating is to prevent hosts, people, from getting sick with it," he says. "That's why it's so important people should get immunized and wear masks."

Both Nelson and Ray point out that it is in the best interest of the virus to evolve to be more transmissible and spread to more people. In contrast, a virus that causes people to get so sick that they isolate or die, thus halting transmission, works against viruses surviving evolutionarily.

Some viruses also mutate to become milder over time, but that has not been the case with SARS-CoV-2, Ray says.

Mutations Not the Only Concern

Viruses have another mechanism that produces new strains, and it works even more quickly than mutations. Recombination, as it's known, can occur when a person is infected with two different strains of the same virus. If the two versions enter the same cell, the viruses can swap genetic material and produce a third, altogether different strain.

Recombination has already been seen with influenza strains, where H and N genetic segments are swapped to yield H1N1, H1N2, and H3N2 versions of the flu, for example.

"In the early days of SARS-CoV-2 there was so little diversity that recombination did not matter," Ray says. However, there are now distinct lineages of the virus circulating globally. If two of these lineages swap segments "this would make a very new viral sequence in one step without having to mutate to gain those differences."

"The more diverse the strains that are circulating, the bigger a possibility this is," Ray says.

Protected, for Now

Walensky's sober warning came at the same time the CDC released new guidance calling for the wearing of masks indoors in schools and in any location in the country where COVID-19 cases surpass 50 people per 100,000, also known as substantial or high transmission areas.

On a positive note, Walensky says: "Right now, fortunately, we are not there. The vaccines operate really well in protecting us from severe disease and death."