Most major Gulf shares struggled for momentum on Wednesday as euphoria in the markets over positive news on COVID-19 vaccine development fizzled out after a string of gaining sessions, while Dubai bucked the trend in morning trade.

Two U.S. drugmakers - Pfizer Inc and Moderna Inc - within a gap of a week came out with encouraging news on the effectiveness of the vaccine against the pandemic, boosting hopes of a faster-than-expected global economic recovery. 

Oil prices, a crucial impact factor for the financial markets in the region, were mixed as a bigger-than-expected build in U.S. crude stocks and weaker U.S. retail sales stoked fears over fuel demand, although hopes that OPEC and its allies will delay a planned rise in oil output lent support. 

Saudi Arabia's benchmark index retreated 0.2%, with lender and index heavyweight Al-Rajhi Bank and Samba Financial Group declining 0.4% and about 1.5%, respectively.

Saudi Arabia called on fellow OPEC+ members on Tuesday to be flexible in responding to oil market needs as it builds the case for a tighter oil production policy in 2021 to tackle weaker demand amid a new wave of the coronavirus pandemic. 

Dubai's main share index added about 0.6%, with Dubai Islamic Bank and Emaar Properties leading the gains, putting on 1.4% and 1.7%, respectively.

The Abu Dhabi index, which has gained for seven straight sessions, traded 0.2% lower.

Losses in financial stocks dragged the benchmark, with lenders First Abu Dhabi Bank and Abu Dhabi Islamic Bank falling 0.6% and 1%, respectively.

Elsewhere, in Qatar, the index fell 0.6%, with Qatar Commercial Bank dragging the benchmark with a 2.4% fall.

(Reporting by Aby Jose Koilparambil in Bengaluru; Editing by Christopher Cushing) ((abyjose.koilparambil@thomsonreuters.com; +91 (0)8061822683;))