There’s new evidence that fast-spreading variants of the coronavirus that causes Covid-19 are more resistant to antibody treatments and vaccines.

Researchers assessed variants first identified in South Africa, Britain and Brazil and found that they can evade antibodies that work well against the original version of the coronavirus that triggered the pandemic.

This means that the new variants – which are expected to become dominant – could reduce the effectiveness of vaccines and antibody-based drugs used to prevent or treat Covid-19, according to investigators from Washington University School of Medicine in St. Louis.

The findings are from laboratory tests of antibodies in the blood of people who’d recovered from infection with the coronavirus or were vaccinated with the Pfizer Covid-19 vaccine.

The researchers also tested antibodies in the blood of mice, hamsters and monkeys that had been vaccinated with an experimental Covid-19 vaccine that was developed at the university and can be given through the nose.

The results showed that much higher levels of antibodies are needed to neutralize the variants.

“We’re concerned that people whom we’d expect to have a protective level of antibodies because they have had Covid-19 or been vaccinated against it, might not be protected against the new variants,” said study senior author Dr. Michael Diamond, professor of medicine and of molecular microbiology and of pathology and immunology.

“There’s wide variation in how much antibody a person produces in response to vaccination or natural infection. Some people produce very high levels, and they would still likely be protected against the new, worrisome variants. But some people, especially older and immunocompromised people, may not make such high levels of antibodies,” he explained in a university news release.

“If the level of antibody needed for protection goes up tenfold, as our data indicate it does, they may not have enough. The concern is that the people who need protection the most are the ones least likely to have it,” Diamond said.

He noted that it’s not known what the consequences of the new variants will be yet.

“Antibodies are not the only measure of protection; other elements of the immune system may be able to compensate for increased resistance to antibodies. That’s going to be determined over time, epidemiologically, as we see what happens as these variants spread,” Diamond said.

“Will we see reinfections? Will we see vaccines lose efficacy and drug resistance emerge? I hope not,” he said. “But it’s clear that we will need to continually screen antibodies to make sure they’re still working as new variants arise and spread and potentially adjust our vaccine and antibody-treatment strategies.”

The study was published Thursday in the journal Nature Medicine.