JOHANNESBURG, Dec 30 (Reuters) - South Africa"s rand was flat in thin trade on Thursday as the currency struggled to make meaningful gains against a stronger dollar, while stocks edged higher. By 1505 GMT, the rand traded at 15.9450 against the dollar, unchanged from previous close. The dollar ticked up against major rival currencies as investors remained cautiously optimistic about the economic consequences of a surge in cases of the Omicron coronavirus variant. read more Researchers said on Thursday that a booster dose of Johnson & Johnson Inc"s (JNJ.N) single-dose COVID-19 vaccine was 84% effective at preventing hospitalisation in South African healthcare workers who became infected as the Omicron variant spread. read more The rand was expected to remain volatile in holiday-thinned trade. "Thin markets and low liquidity could see the rand trade above R16.00 in the short term," Andre Cilliers, Currency Strategist at TreasuryONE, said. On the stock market, the Top-40 (.JTOPI) index closed 0.77% higher at 67,129 points while the broader all-share (.JALSH) was up 0.75% to 73,786 points. In fixed income, the yield on the benchmark 2030 government bond was up 3 basis point at 9.430%.