Norway's health authorities judge countries – or regions, in the case of fellow Nordic countries – as 'green' if the rate of new coronavirus infections is less than 20 cases per 100,000 people, meaning Norwegian residents can travel there.

Countries or Nordic regions which do not meet this criterion are classed as 'red', meaning the Ministry of Foreign Affairs advises against travel that is not strictly necessary to these countries, and self-quarantine is required for travellers returning or arriving from them. This also means people cannot travel from 'red' regions to Norway for tourism.

Denmark operates a similar system of using the rate of infection per 100,000 people to determine whether or not to advise travel, but the criteria are applied slightly differently.

As a result, as of July 27th Denmark allows travel to and from 12 Swedish regions or län: Blekinge, Halland, Jämtland, Härjedalen, Kalmar, Kronoberg, Skåne, Sörmland, Uppsala, Värmland, Västerbotten, Örebro and Östergötland.

Norway, meanwhile, accepts travel to and from seven län: Blekinge, Kalmar, Kronoberg, Skåne, Värmland, Örebro and Östergötland.

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The relative health authorities from the respective countries, the Norwegian Institute of Public Health (NIPH) and Denmark’s infectious disease institute SSI, met earlier this year to discuss common criteria for Nordic travel and agreed on the limit of 20 cases per 100,000 people.

But the limit is applied differently by each country after a unilateral Norwegian decision to tighten its requirement, VG writes.

In order for Norway to allow travel to a Swedish region, that region must have registered fewer than 20 coronavirus infections per 100,000 residents in total over the past two weeks.

According to the original limit agreed with Denmark, the infection criterion is 20 per 100,000 residents on average.

This means that the number of new infections over a two-week period will give a different value for the criteria used by Norway (two-week running total) and Denmark (average of last two weeks).

Norway decided to make its requirement stricter when it began to allow tourism to Europe from July 10th, meaning that a stricter demand was placed on allowing travel outside of the Nordic countries, but also applied to the Nordic countries, to where travel was already open.

NIPH advised stricter requirements for the non-Nordic countries, but the government did not want to give those countries more favourable conditions and decided on a blanket application of the stricter criteria, according to NRK’s report.

“The government concluded that the criterion for all new cases should be the same for Scandinavia and the rest of the EEA/Schengen area. It was therefore changed to ’20 new cases per 100,000 residents in the last two weeks’, as the FHI and Norwegian Directorate of Health had proposed for the EEA/Schengen area,” Anne Grethe Erlandsen, State Secretary at the Ministry of Health and Care Services, told VG via email.

Denmark meanwhile chose to apply the less strict interpretation to the Nordic region and European countries alike.

Norway is currently imposing a quarantine requirement on travellers arriving from Spain, a country still considered ‘open’ by Danish authorities at the time of writing.