(CNN) — Global air transport will not recover from the coronavirus crisis until 2024, the International Air Transport Association (IATA) announced Tuesday.

This is one year after the previous projection that the airline agency had made.

Representing 290 airlines, IATA attributed the slow recovery to several factors, including lack of consumer confidence, declining business travel, and new coronavirus spikes in the United States and elsewhere.

The revised baseline forecast is that international passenger traffic will drop 55% in 2020 compared to 2019. In April, IATA had forecast the drop to be 46%.

Passenger numbers are expected to increase 62% next year, but will remain nearly 30% lower compared to the pre-coronavirus era. Full recovery to pre-pandemic levels would not take place in four years.

“Passenger traffic bottomed out in April, but the strength of the rebound has been very weak,” Alexandre de Juniac, IATA CEO and Executive, said in a statement. “The improvement we have seen has been in domestic flights,” he added.

Not surprisingly, short-haul travel is expected to recover faster than long-haul, due to passenger comfort levels, but also because international markets remain largely closed.

“Consumer confidence is weakened and not helped by the UK weekend decision to impose a general quarantine on all travelers returning from Spain,” de Juniac said.

The pandemic bleeds tourism in Spain 2:27

The British government took a surprising turn in its travel policy between the United Kingdom and Spain on Saturday, reestablishing with immediate effect the 14-day quarantine for all travelers arriving from the popular tourist destination, after an increase in cases of coronavirus in the country.

The decision caught many British tourists by surprise, having left shortly after classes ended in the summer. British Foreign Secretary Dominic Raab defended the move and told Sky News that “the decision was made as quickly as possible.” “We cannot apologize for doing it,” he said.

In terms of domestic traffic, China’s airlines lead the recovery, with 35.5% less traffic in June compared to the same period in 2019, a figure better than the decrease of 46.3% in May.

Argentine tourism industry fears for its continuity 2:59

IATA says that scientific advances in the fight against covid-19, including the development of a successful vaccine, could allow for a faster recovery. But for now, the future looks bleak.

“In many parts of the world infections continue to rise,” said de Juniac. “All this points to a longer recovery period and more pain for the industry and the global economy,” he added.

As airlines struggle financially, governments will need to continue relief measures to prevent them from sinking, the agency said.

“Summer, the busiest season in our industry, is passing quickly,” said de Juniac. He added that there was “little chance of a rebound in international air travel unless governments act quickly and decisively to find alternatives to border closings, the reopens that start and stop destroying traveler confidence and the quarantine that kills the demand”.