One of the three variants first appeared in the United Kingdom and another in South Africa, PAHO said in a press release on Thursday.

"The two variants detected in the United Kingdom so far do not appear to have generated community transmission in the region of the Americas," PAHO Incident Manager Sylvain Aldighieri said. "So far, cases appear to be limited to people traveling from the two countries or connected to people traveling from those countries."

The third variant, detected in the state of Amazonas, Brazil, is most prevalent locally and researchers have recently suggested a causal link with recent increases in COVID-19 hospitalization in the city of Manus, PAHO said.

The UK and South African mutations appear to pose a higher risk of death than the original virus from China, according to recent research cited by the PAHO. Media reports indicate that both also are more contagious.

Two approved US vaccines – Moderna and Pfizer-BioNTech - create an immunity to both strains, according to both companies, which also say they are developing booster shots that could be needed for future mutations.