Spot gold sank below $1,900 per ounce during early hours of trading, down 5.3% to $1,853.42 by 11:15 a.m. ET. This marks its biggest single-day slide since August.

US gold futures also declined 5.0% to $1,853.70 per ounce in New York.

Equities surged after Pfizer said its experimental covid-19 vaccine was more than 90% effective. Pfizer and German partner BioNTech SE said they expect to seek US emergency use authorization later this month.

“(The news) really exceeded everyone’s best-case scenarios. There was growing nervousness that we might not get a strong vaccine result, so this unleashed the risk-on trade and for gold, signaled a massive exodus of safe-haven plays,” Edward Moya, senior market analyst at OANDA, told Reuters.

Moya added that “the economy is still in need of much support and only 50 million (vaccine) doses will be available, so we’re not in the clear with the virus and the calls for stimulus will be growing.”

“Gold is taking the hardest hit so far on the Pfizer news,” said Janet Mirasola, managing director at Sucden Futures.

“The selloff was likely a reaction from investors who piled in to gold recently, convinced that a Biden win be positive for the precious metals and negative for the US dollar,” she said.

Gold, traditionally a hedge against currency debasement and inflation, has climbed 24% so far this year, mainly driven by the unprecedented levels of stimulus measures around the globe.

Optimism that a vaccine is imminent may slow or diminish further stimulus measures to support economies ravaged by shutdowns.

The precious metal has now erased all its gains since the US election, when hopes for more fiscal stimulus helped prices break out of a narrow trading range.