EMERGING MARKETS-Currencies, stocks fall on vaccine efficacy worries

* Moderna CEO warns COVID-19 jabs less effective against Omicron

* MSCI EM stocks index set for monthly decline of 4%

* Turkey's lira falls for third straight session

By Shreyashi Sanyal

Nov 30 (Reuters) - Most emerging market currencies dipped on Tuesday on doubts over how effective COVID-19 vaccines are against the Omicron variant, while a gauge for stocks in the developing world was set for its biggest monthly decline in two months.

U.S. drugmaker Moderna's chief, Stéphane Bancel, warned that COVID-19 vaccines were unlikely to be as effective against the Omicron variant of the coronavirus as they have been against the Delta version.

The MSCI's index for emerging market stocks fell 0.4%, set for monthly declines of 4%.

"This is not really new news relative to the last 3-4 days given what we know about the new mutation but the market is picking up on the explicit comments," said Deutsche Bank strategist Jim Reid.

"In reality, the evidence is still incredibly limited on this question, and nothing from the Moderna CEO overnight changes that."

The warning comes a day after global financial markets started the week on firm footing, with analysts pointing to the new variant as a cause for central banks to rein in recent tightening of monetary policy.

Currencies in Asia gave back early gains, while units in Europe, Middle East and Africa were trading flat to lower by 0919 GMT. The drop in developing world currencies was also contained by a weaker U.S. dollar.

South Africa's rand dipped 0.1%, while stocks in the region logged the smallest declines among peers on higher gold prices.

Russia's rouble fell 0.4%, with sliding oil prices to blame. The Russian central bank said it will pursue monetary policy that will bring inflation back to its 4% target by the end of 2022.

LIRA TROUBLES LINGER

Turkey's lira fell in volatile trading for the third day in a row, amid a very low interest rate environment. Turkish President Tayyip Erdogan pledged on Monday to never defend interest rate hikes nor compromise on the issue.

Erdogan's tough stance on keeping interest rates low and influence over the country's central bank has pushed the lira to all-time lows, with the currency losing over 42% this year.

"What has been more interesting over the past couple of days is that the central bank and regulators have begun to intervene in various ways, targeting market participants with short lira positions," said Tatha Ghose, FX and EM analyst at Commerzbank.

"This shows that the authorities are not really comfortable with lira depreciation no matter how much they say that they want a weak lira."

Data showed Turkey's economy grew 7.4% year-on-year in the third quarter, meeting expectations failing to ease concerns about monetary policy.

For GRAPHIC on emerging market FX performance in 2021, see http://tmsnrt.rs/2egbfVh For GRAPHIC on MSCI emerging index performance in 2021, see https://tmsnrt.rs/2OusNdX

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For RUSSIAN market report, see (Reporting by Shreyashi Sanyal in Bengaluru, editing by Ed Osmond)