Asian currencies struggled to find direction on Wednesday after a report raised questions about the effectiveness of an early-stage COVID-19 trial vaccine, ending the risk-on momentum that had boosted the region's riskier assets in the previous session.

Most stock markets in the region inched down and the few trading in the black saw only incremental gains, after a subdued session on Wall Street. The Indonesian rupiah notched firm gains, rising about 0.4% to 14,685 against the dollar, after the central bank unexpectedly stood pat on interest rates, citing the currency's stability as its key priority. Meanwhile, the Thai baht was steady ahead of a monetary policy decision due around 0700 GMT, where the Bank of Thailand is widely expected to cut its benchmark interest rate to a new low.