This is an interesting question, as Norway's population was known to live among the coast and engage in trade; just like the Balkan's (I'll include the Byzantine empire here) were placed alongside a major trade route. I don't want to just sum it up as, trade routes and isolation, so I will try my best to cover the Balkans. Mods, delete if not acceptable.
The plague was in the Balkan's before the Black Death arrived, Yersinia pestis was common across Europe years before Black Death, and after. One of the largest outbreaks other than B.D., The Plague of Justinian, occurred (541) years before (1346). In Constantinople "the number of dead reached five thousand a day," and effectively wiped out half of the population within the region. Now, nearly a thousand years is plenty of time to build up a population, and the plague would continue to strike the region on and off until the BD.
Let's jump forward. In 1346 Trebizond was struck with the plague, it then travels into Constantinople. The Mediterranean was decimated by the plague, and the Balkans must be included within this geographic group. One of the issues with the Balkans during the plague is their record keeping. The Byzantine Empire had records that were entwined within one another; lacking demographic data and literary accounts make these numbers ambiguous at best; we see the plague residing in the Balkans for as long as 14 years, constantly hitting the population. The initial 1346 loss may not have been much, but the population experienced such frequent resurgence that it is discrediting to say 1/3 of the population wasn't killed. The lack of records certainly plays a role in this, alongside Western scholarship.
But wait, the Balkans includes Serbs, not just Byzantines. That where scholarship falls short. I looked for ~5 hours to find a source. There are mentions of Serbian plagues in the 15th, 17th century, 19th, and early 20th centuries, but I was unable to find any English sources. There are around 1,000 Serbian medieval documents in existence. That isn't to say there wasn't much written. Serbian literature was young, only developing in the 11th century by Saint Sava. Literature of that era is limited, and could have been stunted by the plague. Only the bones know the Black Death's extent, and why it wasn't as aggressive in the central Balkans.
So, lack of records and constant waves of the plague have created a great deal of uncertainty about the Balkan region during the Plague.
Joshua North, “The Death Toll of Justinian’s Plague and Its Effect on the Byzantine Empire,” Armstrong Undergraduate Journal of History 3, no. 1 (Jan. 2013).
M Thomas P Gilbert Yersinia pestis: one pandemic, two pandemics, three pandemics, more? The Lancet Infectious Diseases, Volume 14, Issue 4, April 2014, Pages 264-265
McEvedy, Colin. "The Bubonic Plague." Scientific American 258, no. 2 (1988): 118-23. http://www.jstor.org.proxybz.lib.montana.edu/stable/24988987.
(This was the BEST source) Epidemic waves of the Black Death in the Byzantine Empire (1347-1453 AD) Ondate epidemiche della Morte Nera nell’Impero Bizantino (1347-1453 d.C.) Costas Tsiamis, Effie Poulakou-Rebelakou, Athanassios Tsakris, Eleni Petridou
Inadequate Burials as an Important Factor in Plague Epidemic amongst Serbs in the Habsburg Monarchy by the End of the 18th Century: A Historical Analysis Goran Vasin, Snežana Božanić, Milica Kisić Božić History Department, Faculty of Philosophy, University of Novi Sad, Novi Sad, Serbia (Неадекватно сахрањивање као важан фактор у епидемијама куге код Срба у Хабзбуршкој монархији крајем 18. века – историјска анализа)
Đorđe Bubalo, Pragmatic Literacy in Medieval Serbia, Volume 29 of Utrecht studies in medieval literacy, 2014