The major concern is that Covid-19 mutations could undercut the effectiveness of the vaccines. | Emmanuel Dunand/AFP via Getty Images

The variant carries mutations that may weaken the effect of vaccines.

On January 15, US public health officials warned that a more contagious variant of the coronavirus that causes Covid-19 could dominate infections in the United States by March. That grim warning referred to B.1.1.7, a variant that was first identified in the United Kingdom.

But now, one week later, scientists are increasingly concerned about another variant that emerged in South Africa.

There’s evidence from several small, and not-yet-peer-reviewed, studies that mutations in the South Africa variant — known as 501Y.V2 and already present in at least 23 countries — may have a higher risk of Covid-19 reinfection in people who’ve already been sick and still should have some immunity