It would be irrational, legally indefensible and contrary to the public interest for government to mandate vaccines absent any evidence that the vaccines are effective in stopping the spread of the pathogen they target. Yet that’s exactly what’s happening here. 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.