Geneva, Switzerland - With the US set to exit the World Health Organization on Thursday at President Donald Trump's direction, the UN agency's chief urged a last-minute U-turn.

The full withdrawal is effective as of January 22, a year and a day since Trump issued an executive order shortly after his inauguration.

Technically, one of the conditions for withdrawal has not been met as the US failed to pay its contributions in full as agreed. However, the WHO has no means of demanding the money or refusing the withdrawal.

"I hope that the US will reconsider its decision and rejoin WHO," Director General Tedros Adhanom Ghebreyesus said in Geneva, adding that everyone loses with the move.

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"Withdrawal is a loss for the US and also a loss for the rest of the world."

Among other things, the WHO has early warning systems for outbreaks of potentially dangerous diseases. It also coordinates the composition of flu vaccines for the coming season, after analyzing the pathogens circulating worldwide.

The US is no longer participating in either of these activities.

Trump tried to withdraw from the organization during his first term in office, but his successor, Joe Biden, reversed course.

Under the Republican, the US has shunned international and multilateral fora, instead pursuing a so-called "peace through strength" policy of brute force and coercion.