LONDON, Jan 4 (Reuters) - It is not sustainable to give COVID-19 booster shots every 3 to 6 months in the long term, Britain"s chief scientific adviser said on Tuesday, even though the booster rollout is needed in the short term to combat the Omicron variant. "It would be a situation that isn"t tenable to say everyone"s going to need to be having another vaccine every three or six months. That"s not the long-term view of where this goes to," Patrick Vallance said at a news conference, adding that annual booster shots against COVID-19 might be necessary, similar to flu shots. "We needed to get boosted for this variant at this moment. So I think there"ll be a change over time and this will settle into a much more routine type of vaccine programme."