In tort law, there's something called market share liability. Say you come down with a medical condition that you contend was caused by a certain product. If there is significant uncertainty about which entity manufactured the product that caused you to become ill, courts will sometimes calculate damages based on the market shares of the alleged tortfeasors: if Firm X made 30% of the allegedly harmful product, it is liable for 30% of the damages, and so on. This is not a liability allocation scheme I find particularly desirable, but it is often advanced by plaintiffs.
This is all brought to mind by Tom and Apollo's discussion of parents who refuse to vaccinate their children even though that puts others at risk of injury and death. Apollo grimly notes that they might become the targets of lawsuits by parents whose children contracted a fatal or debilitating disease which is generally prevented by vaccination. (Even the vaccinated can get these diseases, as protection is never 100% and the immunocompromised do not benefit.) In an outbreak scenario, it may be unclear which child actually infected the infant plaintiff. Would it be consistent with precedent to simply split the damages among the infected, non-vaccinated children? In the alternative, parents wishing to opt out of vaccination could be required to purchase a bond covering a share of medical expenses for sickened children in their school district.
Perhaps it's sufficiently straightforward to determine the infection vectors and individual suits would be better. But since the anti-vaccine crowd has been so quick to respond to the recent court decision awarding damages to a child plaintiff who contended that vaccines caused her to become ill, it would be interesting to see if they were similarly influenced by liability going the other way. Knowing that you would be responsible for a share of damages of any vaccinated children who fell ill during an outbreak might be quite motivating.