EMERGING MARKETS-Latam FX up on vaccine optimism, Chile's peso breaks 4-day losing streak

* Chilean peso up after central bank leaves rates unchanged * Argentina central bank lowers Leliq rate to 36% * Mexican peso outperforms Latam peers for the week (Updates prices throughout) By Shreyashi Sanyal Oct 16 (Reuters) - Latin American currencies rose on Friday after Pfizer Inc said it could apply for U.S. authorization of its COVID-19 vaccine as early as late November, while Chile's peso rose as its central bank held interest rates steady in its latest policy meeting. News of Pfizer Inc's vaccine, which the drugmaker is developing with German partner BioNTech, comes after global markets were jolted by the halting of two high-profiled COVID-19 vaccine trials earlier in the week. The MSCI's index for Latin American currencies rose 0.1% but was headed for a weekly decline of more than 1%. Chile's peso rose 1%, making gains for the first time in five day after the country's central bank left its benchmark rate steady at 0.5% on Thursday, maintaining its efforts to revive the economy amid the coronavirus pandemic. The peso was also supported by strengthening prices of copper, Chile's biggest export, as demand from China continued to improve. Mexico's peso added 0.8%, and was set to outpace its Latam peers for the week. The country's currency has been benefiting from an economic rebound in the United States, its main trading partner. The Argentine peso held steady after the central bank said on Thursday it will lower the benchmark Leliq rate to 36% from the previous level of 37%, while raising the reverse repo rate three points to 30%, as part of a wider push to harmonize interest rates. "The lack of a clear and comprehensive reaction by the authorities to the notorious denachoring in expectations is creating a vicious circle and leading to a fast deterioration in the economic situation in the country," emerging markers FX strategists at Citigroup said. Emerging market currencies are also exposed to volatility in the run-up to the U.S. presidential election in November, with analysts pointing to a Democratic sweep as the most favorable outcome for these currencies. The Brazilian real weakened 0.2%, the only decliner among major currencies in Latin America, as investors remained doubtful about the government's ability to fund a new fiscal program without surpassing its spending ceiling. Key Latin American stock indexes and currencies: Stock indexes Latest Daily % change MSCI Emerging Markets 1125.75 0.46 MSCI LatAm 1905.80 -0.2 Brazil Bovespa 98529.00 -0.53 Mexico IPC 38093.69 0.09 Chile IPSA 3672.36 0.29 Argentina MerVal 48998.38 1.574 Colombia COLCAP 1169.11 0.27 Currencies Latest Daily % change Brazil real 5.6373 -0.27 Mexico peso 21.1010 0.82 Chile peso 796 0.90 Colombia peso 3846.1 0.06 Peru sol 3.5817 -0.03 Argentina peso (interbank) 77.5200 -0.05 Argentina peso (parallel) 174 -1.72 (Reporting by Shreyashi Sanyal in Bengaluru Editing by Nick Zieminski and Steve Orlofsky)