WASHINGTON — Dr. Anthony Fauci is warning that a surge of coronavirus cases in Europe could foreshadow a similar surge in the United States.

Fauci, the nation’s top infectious disease doctor, is urging Americans to remain cautious while the nation races to vaccinate its citizens.

In an interview on ABC’s “Good Morning America,” Faucis says he is “optimistic” of the vaccines’ effectiveness and expressed hope that AstraZeneca’s vaccine could join the arsenal of inoculations.

He deemed it an “unforced error” that the company may have used outdated data in a clinical trial, perhaps casting doubt on its effectiveness. But he says Americans should take comfort knowing the FDA would conduct an independent review before it was approved for use in the United States.