BERLIN, Dec 22 (Reuters) - The Omicron variant will become the dominant coronavirus strain in Germany within three weeks and the country has ordered 80 million doses of Omicron-specific vaccine for delivery in April or May, health officials said on Wednesday. "An offensive booster campaign is our most important building block in the fight against Omicron," German health minister Karl Lauterbach told a news conference on Wednesday. "The level of protection against severe COVID-19 symptoms after a booster shot is very high. I would estimate it goes well over 90%," he said. However, despite the accelerated booster rollout, Lothar Wieler, president of Germany"s Robert Koch Institute (RKI) for infectious diseases, said people should limit contacts to an absolute minimum. "Christmas should not become the spark that starts the Omicron blaze," Wieler told the same news conference. On Tuesday, German officials agreed to impose limits on private gatherings, close night clubs and discos and ban spectators at football matches from Dec. 28. Germany reported 45,659 new coronavirus cases on Wednesday, 5,642 fewer than a week ago, while the death toll rose by 510. Lauterbach said that a fourth vaccination will be necessary due to the Omicron variant. Germany has ordered 80 million doses of a vaccine made by BioNTech (22UAy.DE) specifically targeting Omicron that should arrive in April or May. It has also ordered four million doses of the newly approved Novavax vaccine - seen as more acceptable to vaccine sceptics - and 11 million doses of the new Valneva shot, which is waiting for marketing authorisation, Lauterbach said. The Novavax shots will arrive in the country in January, he added.