The panel argued that the WHO's Emergency Committee should have declared the outbreak in China an international emergency a week earlier than it did.
It should have done so at its first meeting on 22 January last year [2020], the report said, instead of waiting until 30 January.
The month following the WHO's declaration was "lost" as countries failed to take appropriate measures to halt the spread of the virus.
The WHO was then hindered by its own regulations that travel restrictions should be a last resort, the panel said, adding that Europe and the US wasted the entire month of February and acted only when their hospitals began to fill up.
Panel co-chair and former New Zealand Prime Minister Helen Clark said it was "critical to have an empowered WHO".
"If travel restrictions had been imposed more quickly, more widely, again that would have been a serious inhibition on the rapid transmission of the disease and that remains the same today," she added.