The World Health Organization's (WHO) head on Tuesday welcomed the United States' move to join a WHO-backed program to accelerate tools to fight COVID-19, as President Joe Biden reverses the Trump administration's course.

The program, formally called Access to COVID-19 Tools (ACT) Accelerator, is raising money to develop vaccines, diagnostics and treatments to tackle the pandemic, but still faces a roughly $27 billion funding gap, WHO director general Tedros Adhanom Ghebreyesus said.

Tedros highlighted the importance of the U.S. decision to join the effort as he reiterated fears that international collaboration is growing increasingly fragmented, prolonging the pandemic even as new vaccines win approval.