JOHANNESBURG, Dec 29 (Reuters) - South Africa"s rand inched lower against the dollar on Wednesday, as the currency struggled to make gains in holiday-thinned trade in the last week of 2021 despite increased appetite for riskier assets globally. By 1505 GMT, the rand was 15.8950 against the dollar, 0.82% weaker than its previous close. "A break above the R15.85 level could open the way for a move back to the R15.95/R16.00 area," Andre Cilliers, a currency strategist at TreasuryONE, said. Trading was thin as most traders took time off for Christmas or the end of the year, while optimism that the Omicron coronavirus variant would not derail global economic momentum was the main driver of risk appetite. On the stock market, the Top-40 (.JTOPI) index edged 1.14%higher to 66,613 points and the broader all-share (.JALSH) was up 1.1% at 73,238 points. In fixed income, the yield on the benchmark 2030 government bond was flat at 9.4%.