Delta’s trajectory in the U.K. and elsewhere offers another possible reason for guarded optimism. The variant first spread explosively, but then case rates declined precipitously, most likely because these countries sharply curtailed super-spreading events. The U.K., which has a higher rate of vaccination than the U.S., did not experience the spike we’ve seen in deaths and hospitalizations associated with Delta.

Indeed, in places with high vaccination rates, including much of the U.S., the worst is over: There will be many breakthrough infections, but 80% of the most vulnerable Americans are fully vaccinated, which means that the death rate will be much lower than it once was. Although Covid will remain a deadly threat for the unvaccinated, for the vaccinated—unless more dangerous variants emerge—Delta will have a risk of death roughly similar to that of flu.

Of course, mortality from the flu is already too high, and we will have to face new risks, including that of the post-viral syndrome known as “long Covid.” But the advent of new vaccine technologies, particularly mRNA, could usher in a new golden era in combating infectious disease. Norovirus, which causes tens of millions of illnesses a year, can likely be prevented with vaccination. Respiratory syncytial virus, which causes millions of illnesses, sends tens of thousands of children to the hospital each year and kills thousands of seniors, could become a distant memory. Even bacterial infections, such as methicillin-resistant staphylococcus aureus, may be tamed by vaccination.