but it also finds a fourth dose may not provide enough of those antibodies to protect against the omicron variant. let's bring in cnn senior medical continue eliza-- correspondent elizabeth cohen. >> in israel, several weeks ago they started giving fourth doses to people who were immune compromised, to people who were 60 years of age or older, and also to health care workers. so they decided to see, when we give it to health care workers, what happens, let's take a look at what shiba did, they gave fourth doses to 274 health care workers, some got pfizer, some got moderna. the fourth dose did raise antibodies, they weren't sure. they didn't give any data as to whether or not getting that fourth dose did what we want it to do is prevent severe disease,