Covid variants could ‘undermine all of our efforts’ if virus spreads globally, CDC director says

New, highly transmissible Covid-19 variants “stand to reverse” the nation’s control of the pandemic and could “undermine all of our efforts” against the disease if the virus is left to proliferate in different parts of the globe, the head of the U.S. Centers for Disease Control and Prevention said Wednesday.

Top U.S. health officials have warned in recent weeks that the emergence of highly contagious variants, particularly the B.1.1.7 strain that emerged in the U.K., could reverse the current downward trajectory in infections in the U.S. and delay the nation’s recovery from the pandemic.

The problem isn’t isolated to the United States. As the coronavirus spreads, it makes huge numbers of copies of itself, and each version is a little different from the one before it, experts say. As more people become infected, the more likely it is that problematic mutations will arise.