An Israeli hospital on Monday said preliminary research indicates a fourth dose of the coronavirus vaccine provides only limited defence against the omicron variant that is raging around the world.

Sheba Hospital last month began administering the fourth vaccine to more than 270 medical workers 154 who received a Pfizer-BioNtech vaccine and 120 others who received Moderna’s.

All had previously been vaccinated three times with the Pfizer-BioNtech vaccine.

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