JERUSALEM, Dec 12 (Reuters) - Israel announced on Sunday it was adding Britain and Denmark to its "red" list of countries that Israelis are forbidden to visit, citing concern over the spread of the Omicron coronavirus variant. The travel restrictions for Britain and Denmark will go into effect on Wednesday, Sharon Alroy-Preis, Israel"s director of public health, told a news conference. She had also announced that Belgium would be included in the ban but the Health Ministry said later it had reassessed infection rates there and decided to keep the country off the "red" list for now. Israel has already banned the entry of foreigners to try to stem COVID-19 infection rates and has imposed three-to-seven day self-isolation orders for Israelis returning from abroad. At the news conference Alroy-Preis cited the "significant spread of the Omicron variant" abroad in imposing the new restrictions. Some 50 countries, mainly in Africa, have been declared "red" by Israel since the discovery of the highly contagious variant. Health officials said there have been 55 confirmed cases of Omicron infection in Israel, which has been trying to accelerate its vaccination programme while also considering stricter enforcement of mask mandates.