At least four new variants of the coronavirus are keeping scientists awake at night.
One, first identified in southeast England, has now shown up in at least 50 countries and appears to be spreading more efficiently than older variations of the virus. Its appearance has frightened political leaders, who have closed borders and imposed travel restrictions in attempts to curb its spread.
Others, identified in South Africa and Brazil, haven't traveled as far and wide but show a constellation of mutations that have grabbed the attention of geneticists.
B.1.1.7: At the top of the list for researchers in the United States is the B.1.1.7 variant first seen in Britain. The US Centers for Disease Control and Prevention warned last week it could worsen the spread of the pandemic.
While there's nothing like the phrase "mutant new virus" to grab the attention, scientists say so far they are reassured by what they have found: The human immune system can handle the variants that have sprung up so far.
B.1.351: A variant first seen in South Africa called B.1.351 or 501Y.V2, has a different pattern of mutations that causes more physical alterations in the structure of the spike protein than B.1.1.7 does. One important mutation, called E484K, appears to affect the receptor binding domain -- the part of the spike protein most important for attaching to cells.
P.1 and P.2: Two variants of concern have shown up first in Brazil. One, called P.1., has been found in 42% of specimens in one survey done in the Brazilian city of Manaus, and Japanese officials found the variant in four travelers from Brazil. P.2, also first seen in Brazil, caused a flurry of alarm when it turned up in Britain last week in 11 people.
L425R: Finally, there's a new variant seen in California called L425R, and while it's being found commonly, it's not yet clear if it's more transmissible.
Read more about the variants: