Pfizer said Thursday its Covid-19 vaccine blocked 94% of asymptomatic infections in an Israeli study – a result CEO Albert Bourla called "extremely important."

The study, which measured results two weeks after the second dose, also found the vaccine was at least 97% effective against symptomatic Covid cases, hospitalizations and deaths, according to Pfizer, which developed the shot with BioNTech.

The analysis used data collected between Jan. 17 and March 6, when Pfizer's vaccine was the only available shot in the country and when the more transmissible B.1.1.7 variant from the U.K. was the dominant strain.

"This is extremely important ... for society," Bourla said in an interview with CNBC's "Squawk Box." "The asymptomatic carriers and patients are the ones spreading the disease mainly. We were expecting something good in terms of symptomatic," he said, adding the company was not expecting such a "high number" against asymptomatic cases.

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