According to scientists, new variants may already be more transmissible and could also be somewhat resistant to the vaccine.
“These variants are a very real threat to our people and our progress,” Centers for Disease Control and Prevention director Dr. Rochelle Walensky said.
While US experts have been following variants first identified in the United Kingdom and South Africa, they're also seeing red flags in other variants discovered closer to home in Brazil, New York and California.
The virus mutation, which was first discovered in Brazil and called P.1, has already been reported in six US states and Japan. Many of the cases occurred in people who already had recovered from the coronavirus, intensifying concerns about reinfection.
Another type of coronavirus B.1.526 was found first in New York and surrounding states. Like the Brazilian mutation, this strain may be more resistant to a certain course of treatment and vaccination.
A California strain - called B.1.427 or B.1.429- researchers say it’s worth watching after a study suggested it’s associated with increased risk of severe disease and death.
As we reported earlier, WHO director-general Tedros Adhanom Ghebreyesus said on Friday that the Covid-19 pandemic has caused more "mass trauma" than World War II.
"The world has experienced mass trauma because World War Two affected many, many lives," Ghebreyesus said.
He also added that pandemic induced mass trauma is "beyond proportion and even bigger than what the world experienced" after the Second World War.
"Countries have to see it as such, and prepare for that," he warned.