There are many accounts of Viking contact with Native Americans and the plague-type diseases of Europe could have been transmitted during these encounters. Why were these not sufficient to transmit the spread of diseases that were present in Europe at the time? Did the Vikings not have enough exposure to mainland Europe to acquire the diseases? If the diseases spread so rapidly and easily following Columbus's voyage, why not by Leif Erikson's voyage?
Not trying to discourage further discussion, but you may find that this post by /u/Reedstilt has a lot of the info you're curious about.
To add to the reply regarding epidemology and spread of diseases in the old Northern world: Ole Jørgen Benedictow wrote a book about plagues in Norway where he makes one important finding regarding the spread of the 1349 Beubonic plague in Norway and in Europe in general; the report of the spread of the disease slows down in the winter, i.e. the plague didn't travel as far and fast during the winter as it did in the summer. This is mainly due to whatever spreads the plague, it be rats or humans, won't travel in the winter. This goes particularly for the Norwegian viking terretories(Norway, Iceland and Greenland). If you haven't been here in the winter I can tell you that the conditions are pretty much shit from mid-late Spetember until Spring. With no roman roads or infrastructure you will have little travel across land until the snow gets in, and then you'll only use skiis or sleads, limiting your carrying capacity. Rats and mice will be dormant indoors, so you want have any spreading of diseases in that manner. Due to the frequent storms and cold water travel by sea is pretty much out of the question or at best gambling with your life. Along with scarce population any serious disease will kill off the population over the winter.
Another important factor is that for their age, Vikings were actually very hygienic. The British women would look at the Vikings as much more handsome than their British compatriots because they combed their hair and tried to bathe once a week. Good hyegine = less diseases.