How many times have you seen the image? It looms behind newscasters during evening updates, gets handed out on printed fliers and scrolls by in tweet after tweet. It might even show up in your dreams.

But for Alissa Eckert — a medical illustrator at the Centers for Disease Control and Prevention who helped to create what has become the iconic representation of the novel coronavirus — it started out as just another assignment.

On Jan. 21, the day after the C.D.C. activated its emergency operations center for the new coronavirus, Ms. Eckert and her colleague Dan Higgins were asked to create “an identity” for the virus. “Something to grab the public’s attention,” she said. Ms. Eckert expected that whatever they came up with might appear on a few cable news programs, as their creations had in the past.

Instead, as the pandemic spread and intensified, their rendering’s reach did, too. “It started popping up around the world,” she said.

Ms. Eckert uses art to make difficult medical concepts more approachable. For instance the dozens of illustrations of birth defects she’s done over the years can be “a little bit easier for people to look at and understand” than photographs, she said.

Often this means bringing the unseeable into view. One of her favorite recent illustrations, of a cluster of Neisseria gonorrhoeae, the bacteria that cause gonorrhea, was used in a 2019 report on antibiotic resistance. In her portrayal, the bacteria float like jellyfish, their tentacle-like pili intertwined. The aim was to “make them look like they’re really alive,” she said, “so you know to be aware of them.”

Over the years, Ms. Eckert, Mr. Higgins and their colleagues have taken a variety of approaches to viruses. Sometimes, they’ll represent a virus with its main vector — the C.D.C.’s Zika page, for example, highlights mosquitoes. Or they’ll focus on the virus’s symptoms, as they did for Ebola.

But for the coronavirus illustration, they went with what professional medical artists call a “beauty shot”: a detailed, solo close-up.

“We just call attention to the one virus,” she said.

The novel coronavirus, like all viruses, is covered with proteins that give it its character and traits. There are the spike proteins, or S-proteins — the red clusters in the image — which allow the virus to attach to human cells. Envelope or E-proteins, represented by yellow crumbs, help it get into those cells. And membrane proteins, or M-proteins, shown in orange, give the virus its form.

After researching and consulting with scientists, Ms. Eckert and Mr. Higgins found these in the RCSB Protein Data Bank, a repository of protein structures. “We pull from that and compile it into a visualization software,” where they can move each piece around, Ms. Eckert said.

Then, where other portrait artists might layer paint, the team layers programs. One piece of software, Autodesk 3ds Max, is “where all the magic happens,” Ms. Eckert said. “We think of it as our photography studio.” There, they arranged the virus’s parts, and tested different colors, textures and lighting.

They chose a stony texture, wanting it to seem like “something that you could actually touch,” Ms. Eckert said. Other details — like the level of realism and the lighting, which has the spikes cast long shadows — were calibrated to “help display the gravity of the situation and to draw attention,” she said.

And although there are more M-proteins than any of the other structures in the virus, they decided to foreground the spiky S-proteins, whose effectiveness may be responsible for the virus’s rapid spread.

As they were styling the virus, other C.D.C. designers were working on more Covid-19 materials. The illustration “was going to have to go along with the branding,” Ms. Eckert said, so they tried color schemes that matched. Red on gray, with orange and yellow accents, was the most arresting: “It just really stood out.”

The image took about a week to make — a fast turnaround, Ms. Eckert said. She expects its success will set a standard, she said: Next time a novel virus needs to be illustrated, it too will likely get a beauty shot.

And it has certainly spread far and wide. She has seen her illustration turned into cookies and knitting projects. Someone recently told Ms. Eckert that her image haunts them on their occasional trips to the grocery store. If they reach out to touch something, they’ll picture that spiky gray blob and pause.

She was glad to hear it, she said. “It’s out there doing its job.”