JERUSALEM (AP) — An Israeli hospital says preliminary research indicates a fourth dose of the coronavirus vaccine provides only limited defense against the omicron variant that’s raging around the world. Sheba Hospital says the additional dose has boosted people’s levels of antibodies, but not prevented them from being infected with the latest variant. Dr. Gili Regev-Yochay, director of the hospital’s infectious disease unit, said on Monday that the vaccines “offer less protection versus omicron.” Israel is battling a wave of omicron that has sent infections to record levels. The government says it’s shortening quarantine requirements from seven to five days in order to help keep the economy running.