The 19-member panel of independent experts held their sixth meeting in a year under the chairmanship of French expert Didier Houssin, as the death toll from the pandemic neared two million.
The experts issued a series of recommendations, which WHO Director-General Tedros Adhanom Ghebreyesus accepted and sent to the UN agency's 194 member states, a statement said.
"At the present time, do not introduce requirements of proof of vaccination or immunity for international travel as a condition of entry as there are still critical unknowns regarding the efficacy of vaccination in reducing transmission and limited availability of vaccines," the WHO panel said.
"Proof of vaccination should not exempt international travellers from complying with other travel risk reduction measures," it added.
The panel urged countries to monitor virus variants such as those identified by Britain and South Africa to assess the effects on the efficacy of vaccines, drugs and diagnostic tests.
It called for promoting technology transfer to low- and middle-income countries with the potential capacity to accelerate global production of COVID-19 vaccines.Further research was also needed on "critical unknowns about COVID-19 vaccination efficacy on transmission, duration of protection against severe disease and asymptomatic infection" as well as the duration of immunity following infection or vaccination, and protection after a single dose, the panel said.