Mrs Sirleaf was president of Liberia during the Ebola epidemic that started in 2014. It killed 11,000 people in West Africa. New Zealand has been applauded for its handling of the COVID-19 pandemic.
WHO boss, Tedros Adhanom Ghebreyesus, said stakeholders to collaborate to contain the pandemic.
"Through you, the world will understand the truth of what happened and also the solutions to build our future better as one humanity," the AFP news agency quoted Dr Tedros as saying.
The WHO has been criticised for its handling of the pandemic. Notable is the United States which said WHO’s response to the initial outbreak in China was slow and accused the organisation of being too close to the Chinese government.
Dr Tedros said the evaluation will not only look at the WHO’s response but at the response of individual countries as well, our correspondent says.
Dr Tedros said, “Together, we now have a once-in-a-generation opportunity to prove to each other that we can be greater than the sum of our parts."
“Together, we now have a once-in-a-generation opportunity to prove to each other that we can be greater than the sum of our parts."
He added that most countries are yet to put the virus under control, indicating that the greatest threat was not the virus itself, but lack of leadership in dealing with it.