Doctors treating the Israeli Prime Minister Ariel Sharon say it is still too early to give a full prognosis. The 77-year-old is still facing serious health problems, despite responding slightly to stimuli as he is brought out of an artificial coma after lengthy surgery.Sharon has been in hospital since the middle of last week after suffering a massive stroke. His doctors are cautious about the future. Israelis maintaining a vigil for their leader – a man many had seen as their best hope for resolving their conflict with the Palestinians – took heart from the news. But Sharon remains in a coma and doctors still do not know how severely his brain has been damaged.If tests show Sharon is permanently incapacitated and unable to return to office, a caretaker prime minister will officially take over until a general election is held. The five cabinet members from Sharon’s Kadima party are the only eligible candidates. But acting Prime Minister Ehud Olmert is seen as the only real choice.