Nov 30 (Reuters) - Canada's main stock index fell to a one-month low on Tuesday over worries that existing vaccines may not hold up against the COVID-19 Omicron variant, with a decline in crude prices dragging heavyweight oil stocks.

Warnings from U.S. drugmakers Moderna and Regeneron Pharmaceuticals that their COVID-19 vaccines and antibody cocktails could be less effective against the new coronavirus variant intensified selling in global financial markets.

Ottawa Public Health said late on Monday that two more cases of Omicron were detected in the city, bringing Canada's total number of cases to five.

The Toronto Stock Exchange's S&P/TSX composite index was down 104.45 points, or 0.49%, at 21,044.5 as of 09:43 a.m. ET (14:43 GMT), as investors worried about the impact of movement restrictions to curb the spread of the virus.

The day's losses pushed Canada's main stock index marginally into the red for the month, after jumping almost 5% in October.

The energy sector dropped 1.5% as U.S. crude prices were down 3.1% a barrel, while Brent crude lost 3.4%.

"Canada is basically getting caught up in a general pullback in equity markets around the world," said Colin Cieszynski, chief market strategist at SIA Wealth Management.

But Cieszynski said a positive start to bank earnings season after a better-than-expected fourth-quarter profit for Bank of Nova Scotia, and rallying gold prices could support the market as the day progresses.

The materials sector, which includes precious and base metals miners, added 0.6% as gold futures rose 0.7% to $1,793.9 an ounce, while silver gained 1.6%.

The largest percentage gainers on the TSX were Osisko Mining and MAG Silver Corp, followed by New Gold Inc .

Data showed Canada's economy grew at an annualized rate of 5.4% in the third quarter, topping expectations of a 3% growth. October's GDP was set to rise by 0.8% over the previous month.

"Canadian GDP was absolutely fantastic. It showed that the economy really started to turn around in the summertime when it reopened ... But as far as the markets go, Q3 is quite a ways back in the rearview mirror ... the market is focusing on other things now," Cieszynski said.

HIGHLIGHTS

Enbridge Inc lost 1% as analysts said a Canadian regulator's rejection last week of the energy company's plan to sell space long-term on the country's biggest oil pipeline could hit its bottom line.

The TSX posted one new 52-week high and eight new lows.

Across Canadian issues, there were eight new 52-week highs and 26 new lows, with total volume of 55.37 million shares. (Reporting by Susan Mathew and Anisha Sircar in Bengaluru; Editing by Vinay Dwivedi)