South African COVID variant can chip away at vaccine efficacy -- but the vaccine can still save your life

Since the emergence of several new COVID-19 variants across the globe, scientists have been racing to understand their impact on vaccines.

Early laboratory experiments showed worrying signs that one variant -- the one that originated in South Africa -- could become a big problem. And now, two large experiments in thousands of people have confirmed that our current approach to vaccines is unlikely to be as effective against this particular variant.

But it's not all bad news, scientists say. Up against the South African variant, also known as B1.351, an excellent vaccine boasting more than 90% efficacy against disease is still a very good vaccine that can save your life.

The first jolt of potentially worrying news came from Moderna and Pfizer -- both of which have COVID-19 vaccines authorized by the Food and Drug Administration. Working in a laboratory, these companies found clues that their vaccines might not work quite as well against the mutations in the South African variant. Still, these lab studies were difficult to discern, their full impact unclear.

But then came more concrete data from studies in people. One large study from the pharmaceutical company Novavax -- one of the six Operation Warp Speed companies which has yet to win FDA authorization -- showed the vaccine was roughly 90% effective when tested in the U.K. but only 50% effective when tested in South Africa, where the B1.351 variant is dominant.

These results -- the first large study in people -- weighed heavily on some scientists. Almost all the vaccines that have been authorized or are in late-stage development target the original virus's spike protein. The South African variant contains mutations within that crucial target.

"I believe the data imply that other vaccines that use the wild type spike protein or its sequence will be reduced for efficacy against the South African variant," said Akiko Iwasaki, Ph.D., a Yale University immunologist.

"It's fair to assume [Novovax's results] would be similar for all the vaccines because they all target spike, but we should also not freak out," said Angela Rasmussen, Ph.D., a virologist at the Georgetown Center for Global Health Science and Security in Washington, D.C.

The next day, pharmaceutical giant Johnson & Johnson -- testing its own still-experimental one-shot vaccine -- found similar results. Their vaccine was 72% effective in the United States but only 57% in South Africa.

"It is likely that all vaccines will show substantially lower efficacy against the strain that originated in South Africa," said Dr. Dan Barouch, Ph.D., director of the Center for Virology and Vaccine Research at Beth Israel Medical Center in Boston.

Major vaccine makers have announced plans to develop an updated version of their vaccines -- tweaked to address the specific mutations found in the South African variant.

"All the vaccine manufacturers are doing what they should be: getting to work testing reformulated vaccines that should work against the variants," said Rasmussen.

"The best way to combat this variant is to use the spike proteins from the variant as the antigen," said Akiko.

But experts say that although less effective against the South African variant, the current vaccines are likely to save your life if you become infected with it.

In a recent trial, the Johnson & Johnson vaccine, for example, was 85% effective at preventing severe illness and hospitalization -- no matter the variant.

Dr. Anthony Fauci, the nation's top infectious disease doctor, said the average American should focus on how effective the vaccines are against severe illness, despite the inclination to want to know if a vaccine will prevent you from getting sick at all.

On a call with reporters, he said the most important thing "is to keep people out of the hospital and prevent them from getting severe illness."

Other experts agree that we should focus more on preventing hospitalizations and death, and less on mild infections.

"Obviously it's no fun having mild illness," said Dr. Paul Offit, a member of the FDA's advisory committee, director of the Vaccine Education Center and professor of pediatrics in the Division of Infectious Diseases at Children's Hospital of Philadelphia.

"But the real question is, how effective was it at keeping people out of the hospital?" Offit said. "From the standpoint of making a vaccine for this pandemic, your goal is keeping people out of the hospital and out of the morgue."

ABC News' Stephanie Ebbs contributed to this report.