Tedros Adhanom Ghebreyesus stressed the importance of such steps.
The WHO chief also said some countries were reporting shortages of vaccines for other infectious diseases as a result of border closures and disruptions to travel.
US President Donald Trump ordered the suspension of US funding to the agency after accusing it of "severely mismanaging and covering up the spread of the coronavirus".
Tedros insisted that the United Nations health agency had provided sound advice from the beginning "based on the best science and evidence".
The health agency warned earlier this month that more than 100 million children around the world are at risk of missing out on measles vaccinations this year alone due to coronavirus lockdowns. "We don't have any mandate to force countries to implement what we advise them".
"I think that suffices the importance of listening to WHO's advice".
Saudi Arabia abolishes flogging as form of punishment
The Kingdom of Saudi Arabia will conduct 9 million tests for the coronavirus disease after signing a deal with China on Sunday. United Nations human rights experts made an urgent appeal to Saudi Arabia previous year to halt plans to execute them.
"We continue to urge countries to find, isolate, test and treat all cases and trace every contact to ensure these declining trends continue".
"It is up to the countries to reject or accept", he said.
More than 56,000 people have died in the United States, representing more than a quarter of all deaths worldwide.
More than three million people across the globe have been diagnosed with COVID-19, the disease caused by the new respiratory virus, according to data compiled by the Center for Systems Science and Engineering at Johns Hopkins University.
"There is one thing we have not done and that is give up", he said. The total number of cases in mainland China now stands at 82,836, and deaths at 4,633.