Acting chief executive Virginia Messina said world leaders should have placed more emphasis on travel during their discussions.
Her comments followed the summit held over 11-13 June in Cornwall.
"World leaders and their entourages have flown from around the world and proved that travel is safe during the pandemic," said Messina.
"But they have missed a vital opportunity to enable their citizens to travel more freely and agree an immediate further opening of overseas travel."
The summit was preceded by one development on international travel, an agreement between the UK and US to set up a new taskforce to explore the resumption of transatlantic travel.
However, no timeframe for this has been set. UK transport secretary Grant Shapps will oversee the taskforce, with support from senior Department for Transport officials and their US counterparts.
Messina added: "Every day, travel and tourism businesses are losing tens of millions pounds due to governments delaying a safe restart.
"We need to see action immediately to help the sector get back on its feet, a sector which can’t wait any longer if it’s to avoid hundreds of thousands of job losses, in addition to the millions already lost worldwide."
The UK government will formally review its traffic light regime for the first time on 28 June, the first of three checkpoints set out by the Global Travel Taskforce.