(WPIX) —  At least two new COVID-19 variants have hit the United States, and they could be worse than the delta variant in their infectiousness and ability to stand up to vaccines, according to a top medical authority.

The lambda variant, along with another one so new it doesn’t even have a Greek letter name yet, is causing concern, according to Dr. Gregory Poland, director of the Vaccine Research Group at the famed Mayo Clinic in Rochester, Minnesota. So far, the new variant has been called B.1.621.

There now are about 1,500 known cases of the lambda virus mutation in the United States, Poland told NewsNation affiliate WPIX.

“What makes it dangerous is that it’s highly infectious and can resist some of the vaccine-induced immunity and spread easily between people,” he said.

Virus variations compete for supremacy, and the stronger and most resistant forms are the ones that take over and become the most common strains.

With relatively few U.S. cases so far, Poland said it’s not yet clear whether lambda will supplant the delta variant that’s sweeping so much of the country. But he pointed out that lambda is now responsible for about 88% of all COVID-19 cases in Peru “and has really started to spread through South America.”

The B.1.621 variant was discovered early this year in Colombia.

“It recently caused an outbreak in a nursing home in Belgium and killed seven people that were fully vaccinated,” Poland told WPIX. “What is concerning about [it] is that it is now 9% of the cases that have been seen in Miami, Florida.”

Those new variants could spread to the rest of the country. Current vaccines, of course, were not designed to fight the variations that previously didn’t exist. Ideally, there would be new vaccines to battle these variants instead of the plan to provide booster shots of the current vaccine.  But Poland is doubtful that new vaccines can be available in time.

These are precarious times, Poland stressed. The pandemic is far from over, and the ongoing mutations may present big problems.

“If you are unvaccinated, you now enter the most dangerous phase of the pandemic for your health and your family’s health,” he said. “We’re paying the price for the relatively large segment of our population who won’t wear a mask and who won’t get vaccinated.”