WASHINGTON, May 5 (Reuters) - President Joe Biden on Wednesday threw his support behind waiving intellectual property rights for COVID-19 vaccines, bowing to mounting pressure from Democratic lawmakers and more than 100 other countries, but angering pharmaceutical companies.

Biden voiced his support for a waiver - a sharp reversal of the previous U.S. position - in remarks to reporters, followed swiftly by a statement from his top trade negotiator, Katherine Tai, who backed negotiations at the World Trade Organization.

“This is a global health crisis, and the extraordinary circumstances of the COVID-19 pandemic call for extraordinary measures," Tai said in a statement, amid growing concern that big outbreaks in India could allow the rise of vaccine-resistant strains of the deadly virus, undermining a global recovery.

Shares in vaccine makers Moderna Inc (MRNA.O) and Novavax Inc (NVAX.O) dropped several percent in regular trade, although Pfizer Inc (PFE.N)stock fell only slightly.

The head of the World Health Organization, Tedros Adhanom Ghebreyesus, called Biden's move a "MONUMENTAL MOMENT IN THE FIGHT AGAINST #COVID19" on Twitter, and said it reflected "the wisdom and moral leadership of the United States."

Pharmaceutical companies working on vaccines have reported sharp revenue and profit gains during the crisis. The industry's biggest lobby group warned that Biden's unprecedented step would undermine the companies' response to the pandemic and compromise safety.

One industry source said U.S. companies would fight to ensure any waiver agreed upon was as narrow and limited as possible.

Robert W. Baird analyst Brian Skorney said he believed the waiver discussion amounted to grandstanding by the Biden administration and would not kick off a major change in patent law.

"I'm skeptical that it would have any sort of broader long- term impact across the industry," he said.

Biden backed a waiver during the 2020 presidential campaign in which he also promised to re-engage with the world after four years of contentious relations between former President Donald Trump and U.S. allies. Biden has come under intensifying pressure to share U.S. vaccine supply and technology to fight the virus around the globe.

His decision comes amid a devastating outbreak in India, which accounted for 46% of the new COVID-19 cases recorded worldwide last week, and signs that the outbreak is spreading to Nepal, Sri Lanka and other neighbors.