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The study of the Pfizer/BioNTech vaccine which was conducted by the Israeli Clalit health maintenance organization was published on Wednesday in full sin the New England Journal of Medicine.

The study, which was the first big real-world study to be independently reviewed, shows the shot is highly effective at preventing COVID-19.

The research in Israel showed that two doses of the Pfizer shot cut symptomatic COVID-19 cases by 94% across all age groups, and severe illnesses by nearly as much.

The study of about 1.2 million people also showed a single shot was 57% effective in protecting against symptomatic infections after two weeks.

The results of Clalit’s study were close to those in clinical trials last year which found two doses were found to be 95% effective.

“We were surprised because we expected that in the real-world setting, where cold chain is not maintained perfectly and the population is older and sicker, that you will not get as good results as you got in the controlled clinical trials,” senior study author Professor Ran Balicer told Reuters. “But we did and the vaccine worked as well in the real world.”

“We have shown the vaccine to be as effective in very different sub-groups, in the young and in the old in those with no co-morbidities and in those with few co-morbidities,” he added.

The Israeli study also suggests the vaccine is effective against the coronavirus variant first identified in the UK. Researchers said they could not provide a specific level of efficacy, but the variant was the dominant version of the virus in Israel at the time of the study.

The research did not shed light on how the Pfizer shot will fare against the South African variant.