TOKYO, Dec 24 (Reuters) - Japan"s Nikkei index gave up small gains and inched down on Friday, as investor sentiment was dented by news about the first community infections of the Omicron coronavirus variant in Tokyo. The Nikkei share average (.N225) inched down 0.05% to close at 28,782.59, after rising as much as 0.25%. The index posted a 0.83% weekly gain. The broader Topix (.TOPX) slipped 0.13% to 1,986.78 and edged up 0.12% for the week. "The Nikkei changed its course after the news on the community transmission of Omicron in Tokyo. Investors sold shares that are related to an economic reopening," said Shoichi Arisawa, general manager of the investment research department at IwaiCosmo Securities. "But trading was thin with most foreign investors away. Today"s weak finish won"t affect the market after next week when foreigners are back." The Nikkei was trading in positive territory earlier in the session tracking Wall Street"s strong finish, which was underpinned by developments surrounding the Omicron variant. Vaccine makers AstraZeneca (AZN.L) and Novavax Inc (NVAX.O) said their shots protected against Omicron as UK data suggested it may cause proportionally fewer hospital cases than the Delta variant. read more However, public health experts warned the battle against COVID-19 was far from over. In Japan, airline shares (.IAIRL.) and railways (.IRAIL.T) slipped 0.59% and 0.99%, respectively, amid news that four infections with the Omicron variant have been confirmed in the Japanese capital. Nikkei"s declines were offset by gains in chip-making equipment maker Tokyo Electron (8035.T), which rose 1.2%, air-conditioner maker Daikin Industries (6367.T) gaining 1% and medical services platform M3 (2413.T), which rose 1.15%. The Topix was weighed down by phone company NTT (9432.T), which fell 2.16%, and sensor maker Keyence (6861.T), slipping 0.55%.