• One of the key government strategies to support tourism was to waive priority for certain age groups and the medically vulnerable in its vaccination program, instead focusing on the residents of the many Greek islands.
• Data shows that as of Wednesday more than 25% of the Greek population have received at least one dose of a vaccine.
• The British government recently decided to not include Greece on its "green list" of foreign destinations, but the southern nations hopes to be "included soon."

Andreas Patiniotis can't help sounding cheerful as Greece once again welcomes tourists back to the country.

"I'm very happy," said the owner of four hotels in one of Greece's most iconic holiday destinations, Santorini. That feeling is spreading across this entire sunny nation, with the economy relying heavily on international visitors.

Greece's gross domestic product sank more than 8% in 2020. A large part of that was due to the lack of tourists.

This year, the government expects the whole summer season to be double 2020 levels, Alex Patelis, an economic advisor to the Greek prime minister, told CNBC on Thursday.

He said this summer "is going to be much easier than before." Patelis said the industry would have now adjusted to Covid-19 safety rules; the vaccination campaign is underway both domestically and abroad; and travelers are keen to seek out some sun.

In fact, the main message in the government's latest tourism campaign— "All you want is Greece" — looks to lure mainly northern Europeans that are desperate for some warmer weather after more than a year in lockdowns and strict social-distancing measures.

One of the key government strategies to support tourism was to waive priority for certain age groups and the medically vulnerable in its vaccination program, instead focusing on the residents of the many Greek islands. The idea is to ensure that tourist hotspots are protected before the large number of visitors arrive.

Athanasia Kokkinogeni, 31, is fully vaccinated. She told CNBC that in her home island, Kythnos, big hotel chains have been remodeling and upgrading ahead of the summer season.

"In general, there's optimism," she said, noting that some tourists have already started to arrive. The official date for the tourism industry to reopen is Friday but some establishments have been working over the past days to deal with upcoming bookings.

Data from Our World in Data shows that as of Wednesday more than 25% of the Greek population have received at least one dose of a vaccine. This is largely in line with the whole of the European Union, which has around 30% of the adult population vaccinated with at least one dose.

Brits to quarantine?

The 2021 summer season will also depend on whether governments in some countries, such as the U.K. and Germany, lift their quarantine policies for when holidaymakers return from Greece. The two nations are among the most important for Greek tourism.

The British government recently decided to not include Greece on its "green list" of foreign destinations, meaning travelers from England face a period of quarantine when they return from the Mediterranean nation.

"All of tourism is very important," Patelis said. "But we are optimistic we will be included soon," he said regarding the U.K. green list. 

The British government is due to revise its green list every three weeks.

Quarantine requirements are an impediment to tourism. However, the European Union is working on a Covid-19 certificate to promote intra-EU travel. The idea is that people that have received a negative coronavirus test, have been vaccinated, or have recently recovered from the disease will not have to quarantine.

"We hope this will be the last summer like this," Patiniotis in Santorini told CNBC.