U.S. President Joe Biden plans to back a World Trade Organization waiver for vaccine intellectual property (IP) to help countries respond to the COVID-19 pandemic, U.S. Trade Representative Katherine Tai said on Wednesday. 

"This is a global health crisis, and the extraordinary circumstances of the COVID-19 pandemic call for extraordinary measures," Tai said in a statement. 

Shares in vaccine makers Moderna and Novavax dropped several percent in regular trade, although Pfizer stock fell only slightly.

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.

Financial service company 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.

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 percent of the new COVID-19 cases recorded worldwide last week, and signs that the outbreak is spreading to Nepal, Sri Lanka and other neighbors.