How mRNA vaccines can keep up with an ever-changing coronavirus

As new COVID 19 variants are rapidly spreading across the world, vaccine manufacturers are preemptively finding ways to adapt to the emerging threats.

Moderna announced Wednesday it had dosed the first patient in a study to test a booster shot against one of the new variants.

New vaccines typically take many months to invent, develop and refine. But vaccines from Moderna and Pfizer rely on cutting-edge, highly adaptable mRNA technology, which can be rapidly modified to keep up with the virus as it evolves.

These vaccines can be updated like "computer code, where they can be reprogrammed to handle differences," said Dr. John Brownstein, chief innovation officer at Boston Children’s Hospital and an ABC News contributor.

A third vaccine -- Johnson & Johnson's single shot, based on a noninfectious viral vector -- should also be relatively straightforward to update because it also relies on genetic material that can be tweaked.

But among all the currently available vaccines across the globe, those that use mRNA may be the easiest to update against new variants, experts said.

Currently available COVID-19 vaccines are designed to target one specific portion of the virus -- the so-called "spike" protein that helps the virus latch on to our cells. If a new variant develops any mutations within that crucial spike protein, vaccines can be updated.

According to Pfizer and Moderna, the modifications can be made in mere weeks. Based on experiments conducted in laboratories, it looks like their original vaccines will work just as well against almost all of the newly emerged COVID variants. Only one variant, the one that originated in South Africa, showed worrying signs of being able to chip away at vaccine efficacy.

For now, Moderna, Pfizer and other companies are exploring updated booster shots against the South African variant out of an abundance of caution.

"The variants haven't crossed the line yet," said Dr. Paul Offit, a professor of pediatrics in the division of infectious diseases at Children's Hospital of Philadelphia and a member of the Food and Drug Administration's vaccine advisory board.

"When that line gets crossed, if that line gets crossed, then I think we're going to have to think about a second-generation vaccine that includes the variants," he said.

Last month, FDA updated its guidelines to give companies a clear path forward about how to test updates to a vaccine in a timely way that still ensures the booster shots are safe.

“Similar to what we do again with seasonal flu shots, we don't have to have the same burden of proof of efficacy and safety in order to release updated versions,” said Brownstein. In other words, people won't have to wait almost a year for each new booster shot.

It's possible the vaccines of the future could offer one-and-done protection against multiple variants. Moderna, for instance, is developing a “multivalent” vaccine that will target the ancestral COVID strain and the new South African strain in a single shot.

But Brownstein said it's more likely everyone will get annual booster shots -- tweaked if needed to address whatever variant happens to be circulating at that time -- just like with the flu shot.

ABC News' Sony Salzman contributed to this report.

Abarna Ramanathan, MD, is a third year internal medicine resident at the Cleveland Clinic, Ohio and a contributor to ABC's Medical Unit.