COVID-19 case numbers, which had been steadily falling in the U.S. since September, have again plateaued. But why have the numbers now stalled in the 70,000s?

More people need to get their shots as soon as possible.

This is the reason President Joe Biden is right to stand by his vaccine requirements. One of them, a mandate that 4 million federal workers be vaccinated, comes into force on Nov. 22. Another, a Labor Department rule that companies with 100 or more employees see that they are either vaccinated or tested weekly, has a deadline of Jan. 4, 2022. (This requirement will apply to about 84 million people, more than 26 million of whom are not yet vaccinated.) Also on Jan. 4, everyone who works at a hospital, nursing home or other health facility that receives payments from Medicare or Medicaid — about 17 million workers at 76,000 facilities — needs to be vaccinated.

More than a dozen state attorneys general filed suit on Friday, arguing that the president lacks the authority to issue vaccine requirements for businesses and that, if they come into effect, they will make it harder for companies in their states to hire people. (A federal appeals court has temporarily halted rollout of the rules.)

Rules are the reason that 92% of New York City’s municipal workers have had at least one shot, and 94% of New York state hospital employees are inoculated. A very small share of employees resist vaccination to the point of losing their jobs. According to a recent Kaiser Family Foundation survey, only 5% of unvaccinated workers say they’ve gone to that extreme.

Opponents call mandates an imposition on liberty or, in the words of Texas Governor Greg Abbott, an “assault on private business.” It’s true they’re an imposition. Highway speed limits and smoking restrictions are also impositions. The point is, they’re amply justified. Public health requires that people refrain from needlessly endangering others.

The new antiviral pills that may soon come on the market from Merck and Pfizer are also not a sufficient reason to back away from vaccine mandates. Vaccines offer broad protection against both infection and severe COVID-19. While the antivirals might be able to prevent infections from becoming so severe as to require hospitalization, they don’t guard against catching and spreading the disease, and this needs to remain a priority.

COVID-19 has proven hard to extinguish. Just when it seems to fade, the case numbers rise again — as they are now doing in Europe — and for reasons that can be frustratingly fuzzy. What’s clear in the U.S. is that the unvaccinated population remains too large for the virus to stop freely circulating. Vaccine mandates are needed to bring the epidemic under control.