Genetic Background Edit
People in the post-Rash societies may or may not have immunity against the Illness. Immunity is heavily documented. There must be either a reliable test method (which may or may not involve magic) or a solid understanding how immunity is inherited from the ancestors. Considering that Icelands Dagrenning Program claims to be able to match egg and sperm donations to recipients in such a way that they can guarantee the child to be immune, the latter seems more likely.
The exact rules used to match participants in the program haven't been given, but the practical examples on the agrees that immunity follows the pattern of an autosomal recessive trait. Assuming that the Dagrenning Program is not capable of selecting individual eggs and sperm, the fact that combining Anna Sigríður Einarsdóttirs husband with an immune woman's donor egg will guarantee an immune child strongly suggests that non-immunity is a completely dominant trait. However, this is only a single case, and there is a chance that Anna's eggs may already have a recessive gene.
The number of chromosomal loci involved in immunity remains unknown. The very low immunity rate in pre-Rash times may be an indication that a number of loci is involved, and the lack of success in developing cures or vaccines suggests that the mechanism of immunity is rather complicated. It may also be possible that the one allele required for immunity is simply rare.
Practical Consequences Edit
Role in the Apocalypse Edit
While there is no confirmation yet that immunity existed in pre-Rash times, its strong ties to genetic mechanisms would strongly suggest it. If so, the fact that the immune survived the actual pandemic (and only started to die en masse when the Rash-generated monsters became a major factor) certainly helped to keep the number of humans at a sustainable level - according to the author, the humanity of the Known World barely avoided extinction by loss of genetic diversity.
The pre-Rash immunity rates are the subject of much speculation. Estimates range from 0.1% to several percent. .01% assumes that the known post-Rash number of immunes is roughly at the pre-Rash level, .5% matches , and the ~50% post-Rash immunity rate implies there were ~85,000 Sami pre-Rash.
Consequences for Individuals Edit
There appears to be little to no dire consequences for individuals. Other than the fact that unimmune persons cannot hold dangerous jobs , the majority of the population functions normally. They have full rights as citizens, and have the chance to have higher education.
On the chance that unimmune people may be exposed to the Illness, sufficient protection is given, along with warnings. When the giant invaded the Dalahästen, breathing masks were immediately handed to all passengers lacking immunity, and they were kept isolated from contaminated surfaces. It is noteworthy that immune train crew members acted rather casually, even though the giant had inflicted open, bleeding wounds on them. This suggests that, whatever its mechanisms are, or regardless of the amount of germs the person is exposed to, immunity is a virtual infection prevention.
It is also implied that those who are immune to the Rash cannot be asymptomatic carriers. This question is raised as Tuuri, Lalli and Emil enter Mora. Tuuri raises concerns that she could hypothetically be carrying the Rash and asks if she should be quarantined before entering the city, since she is not immune. It is dismissed rather quickly. It can be tentatively assumed that those who are immune to the Rash either cannot carry the infection, or are considerably less likely to carry it.
Effects on Society Edit
Icaland currently has an immunity rate of 7% (per the ; in the printed book and its PDF, the number has been changed to 9%), while the rest of the Nordics average 48% immune. In order to protect the non-immune part of society, infectious material is kept out of the safe areas just like monsters are. There are defined decontamination procedures for that purpose.
Needless to say, personnel that maintains the various infection barriers are usually required to be immune themselves, resulting in non-immune being barred from a large number of dangerous professions. These include the staff of the Dalahästen, people patrolling the coasts of Iceland, and grossling hunters. In the case of Reynir, this effect amounted to a feeling of being kept away from the aspects of life that would be interesting, rewarding, and valued by the rest of society. Opinion on immunity varies depending if you're in Iceland VS the other Nordic countries, but it is generally seen in a positive light.