SHANGHAI, Feb 2 (Reuters) - The yuan firmed slightly in thin trade on Tuesday after China reported a drop in coronavirus cases, while investors awaited developments on U.S. President Joe Biden"s $1.9 trillion COVID-19 relief plan. Official data showed that 30 cases were reported in the mainland on Feb. 1, down from 42 cases a day earlier and marking the lowest total since 24 cases were reported on Jan. 2. The drop in infections suggests the country"s worst wave since March 2020 is being stamped out ahead of the Lunar New Year holiday, and helped to offset worries that a flare-up could hurt economic growth following softer manufacturing data on Sunday. Prior to market opening, the People"s Bank of China (PBOC) set the midpoint rate at 6.4736 per dollar, 113 pips or 0.17% weaker than the previous fix of 6.4623. In the spot market, the onshore spot yuan opened at 6.4650 per dollar and was changing hands at 6.4598 at midday, 84 pips firmer than the previous late session close. The onshore yuan fluctuated in a tight range of about 70 pips in morning trade and trading volume also shrunk by midday, with the dollar having traded narrowly in recent sessions, traders said. The market is eyeing developments in U.S. stimulus plan negotiations because a scaled down version would hit risk assets. Some traders expect trading to be thinner in the run up to the week-long Lunar New Year holiday, which starts on Feb. 11. "We maintain an appreciation bias of CNY against USD, with an expectation of a higher possibility of two-way fluctuation for Q1 and the rest of this year," Marco Sun, chief financial markets analyst at MUFG Bank, said in a note. "The renminbi will continue to be supported by improving economic fundamentals and potential sizable FX settlements and sales surplus," Sun added, expecting the yuan to gradually rise to 6.25 per dollar at the end of this year. Sino-U.S. relations, which have heavily affected the yuan"s performance over the last few years, was expected to influence FX markets again this year. China"s top diplomat called on Tuesday for Beijing and Washington to put relations back on a predictable and constructive path, saying the United States should stop meddling in China"s internal affairs. Cash conditions in China"s money market started to loosen up on Tuesday after some key rates surged to near six-year highs recently. The yuan market at 0401 GMT: ONSHORE SPOT: Item Current Previous Change PBOC midpoint 6.4736 6.4623 -0.17% Spot yuan 6.4598 6.4682 0.13% Divergence from -0.21% midpoint* Spot change YTD 1.06% Spot change since 2005 28.12% revaluation Key indexes: Item Current Previous Change Thomson 96.54 96.46 0.1 Reuters/HKEX CNH index Dollar index 90.883 90.972 -0.1 *Divergence of the dollar/yuan exchange rate. Negative number indicates that spot yuan is trading stronger than the midpoint. The People"s Bank of China (PBOC) allows the exchange rate to rise or fall 2% from official midpoint rate it sets each morning. OFFSHORE CNH MARKET Instrument Current Difference from onshore Offshore spot yuan 6.4665 -0.10% * Offshore 6.6079 -2.03% non-deliverable forwards ** *Premium for offshore spot over onshore **Figure reflects difference from PBOC"s official midpoint, since non-deliverable forwards are settled against the midpoint. . (Reporting by Winni Zhou and Andrew Galbraith; Editing by