By Jeremy Samuel Faust & Angela Rasmussen

The United States’ coronavirus vaccine rollout has finally hit its stride, with well over two million doses administered daily. Soon, vaccines will be available to all adults who want them.

Children are the next vaccination frontier. When it comes time to vaccinate them, the same urgency and large-scale coordination efforts driving adult vaccination must continue if we want to sustainably drive down Covid-19 cases and ultimately end the pandemic.

Currently, vaccine demand among adults exceeds the supply. But there’s reason to worry that once children are eligible, vaccination rates for them will initially be far lower and rise more slowly than those seen among adults. Children are much less likely than adults to be hospitalized with Covid-19, and deaths from the disease among kids are rare. Parents may wonder, if Covid-19 is relatively harmless for my children, what’s the hurry?

One reason to vaccinate children quickly is that even a small number of critical Covid-19 cases among children is worth vaccinating against. The burden of long-term effects from Covid-19 in children — including rare but serious cases of inflammatory syndrome — remains unclear, especially since many have asymptomatic infections that go undiagnosed.

But the most important and least recognized reason to vaccinate all children quickly is the possibility that the virus will continue to spread and mutate into more dangerous variants, including ones that could harm both children and adults.

Variants “of concern” first identified in Britain, South Africa, Brazil and California are being closely followed by epidemiologists. Some of these appear more contagious than earlier versions, and at least one of them — B.1.1.7, first observed in Britain — appears to cause a slight uptick in the risk of dying of Covid-19. So far, the vaccines still appear to work well against them.

But we might not be so fortunate with future variants. Viruses acquire mutations as they spread. The more infections there are, the more chances the coronavirus has to mutate. This increases the likelihood that a more dangerous strain could emerge. Variants that cause more severe illness in children are likely to emerge from children themselves, especially with adults becoming less hospitable hosts for infection as vaccinations rise.

Just as important, vaccinating children quickly will improve our odds of emerging from this crisis sooner. The United States is likely to need to vaccinate children to reach herd immunity, as Dr. Anthony Fauci, the nation’s leading infectious disease expert, and others have noted.

Clinical trials to prove that the vaccines are safe for use in children are underway. But we need to be prepared for the reality that those trials will not generate the kinds of blockbuster results that the studies of adults did.