The Supreme Court held in Jacobson v. Massachusetts (1905) that the right to refuse medical treatment could be overcome when society needs to curb the spread of a contagious epidemic. At Friday’s oral argument, all the justices acknowledged that the federal mandates rest on this rationale. But mandating a vaccine to stop the spread of a disease requires evidence that the vaccines will prevent infection or transmission (rather than efficacy against severe outcomes like hospitalization or death). As the World Health Organization puts it, “if mandatory vaccination is considered necessary to interrupt transmission chains and prevent harm to others, there should be sufficient evidence that the vaccine is efficacious in preventing serious infection and/or transmission.” For Omicron, there is as yet no such evidence.

The little data we have suggest the opposite. One preprint study found that after 30 days the Moderna and Pfizer vaccines no longer had any statistically significant positive effect against Omicron infection, and after 90 days, their effect went negative—i.e., vaccinated people were more susceptible to Omicron infection. Confirming this negative efficacy finding, data from Denmark and the Canadian province of Ontario indicate that vaccinated people have higher rates of Omicron infection than unvaccinated people.

Meantime, it has long been known that vaccinated people with breakthrough infections are highly contagious, and preliminary data from all over the world indicate that this is true of Omicron as well.