U.S. drugmaker Pfizer said on Monday that human trials suggest its COVID-19 vaccine is more than 90 percent effective.

Pfizer released the interim results that its vaccine, jointly being developed with German company BioNTech, prevented more than 90 percent of symptomatic infections in a trial of tens of thousands of volunteers. That's much higher than the figures health experts had predicted. 

The findings are based on an interim analysis conducted after 94 of over 43-thousand participants in the trial contracted the virus. 

The volunteers have gotten either the vaccine or a placebo. Pfizer says the 94 infections were mostly in people who had been given a dummy shot. 

The positive results sent stock prices surging as the Dow Jones industrial average soared five percent when the trading began on Monday.