Measures to stem the spread of the coronavirus can only be lifted slowly, if the right public health measures are in place, including significant capacity for contact tracing, the head of the World Health Organization (WHO) said Monday.

“While COVID-19 accelerates very fast, it decelerates much more slowly,” WHO Director-General Tedros Adhanom said at a news conference in Geneva, where journalists asked questions via video.

The U.S. and some countries in Europe have begun to consider the easing of some lockdown conditions around the novel coronavirus, and the WHO has said it is good for them to plan these

Read more: Lift COVID-19 measures slowly, carefully, warns WHO chief