The question of whether the COVID-19 vaccine is efficacious lies with epidemiology. But the question of whether the vaccine should be mandatory begins with economics.

A factory belching pollutants into the air is no different from a contagious person spreading disease in a public space. A factory owner knowingly belches pollution, while an infected person may not be aware that he is contagious. But that distinction mitigates, not eliminates, culpability. A gas station owner who takes appropriate precautions in maintaining underground storage tanks is, nonetheless, responsible for damages caused to others if those tanks leak. Whether the owner is aware that the tanks leak is irrelevant.

Factory pollutants and leaking gasoline create externalities – harms imposed on others. To economists, externalities are a serious problem because, in a free market, they encourage the over-production of the good that creates the externality. Allow frackers to pollute groundwater, and you get more fracking than is socially optimal because the frackers don’t have to pay the price for their pollution. The cure is to force the polluters either to stop polluting or to bear the cost of the pollution. Noise ordinances prevent neighbors from imposing the cost of loud noise on each other. Smoking bans prevent smokers from imposing second-hand smoke on non-smokers. Carbon taxes dissuade manufacturers from releasing greenhouse gasses.

When a person imposes a cost on another, the person violates the other’s property rights. Protection of property rights is so fundamental to the rule of law that, if there is no justification for government involvement here, then there is likely no justification for the government at all.

But what form should the government’s involvement take?

Intervention, after harm occurs, is appropriate when damages are recoverable. A straightforward way to handle this is through a tort system in which the government forces the defendant to compensate the plaintiff. But what if that’s impossible? What if, for example, a defendant could cause millions of dollars in damages, but would have no or inadequate insurance and not be able to raise enough money to pay recompense? In this case, intervention, before the harm occurs, is appropriate. This is the solution we employ with DUI laws. A drunk driver who kills a person creates an unrecoverable cost. There is no amount of money the driver or the insurer can pay to compensate the victim’s family for the harm the driver imposed. The solution is to make DUI a crime even when no harm occurs. The government intervenes before harm can occur so as to reduce the likelihood of the driver creating an unrecoverable cost.

This brings us to mandatory vaccinations. If the harm that a contagious person can impose on another constitutes an unrecoverable cost, then it is appropriate that the government intervene before the harm occurs. One possible form of intervention is to require that people who walk around in public be vaccinated.

This is where the economics argument ends. Followup questions of under what circumstances a contagious person poses harm to others, what the magnitude and probability of that harm may be, to what extent a vaccine mitigates any of this, and what potential harm the vaccine presents to the vaccinated person all bear on whether a vaccine mandate is appropriate. But they are questions for epidemiology. What economics tells us is that the question of whether a vaccine mandate can be appropriate at all begins with property rights.

And this is where those who claim that a vaccine mandate is a rights violation get the argument backward. There is a rights violation at issue, but it isn’t the right of a person to walk around in public unvaccinated. It is the right of everyone else not to have contagion imposed on them.