On Friday morning, the FDA announced that it was expanding the availability of booster shots to cover all adults 18 and older. This move, which many had forecast, came at the end of a week in which new cases of COVID-19 were again increasing across the United States, with the daily average up by 24% since the end of October. 

Over the last few weeks, increasing case numbers generated fears that the next few months could bring on a surge like the one at the end of 2020. From Nov. 1 last year to the peak in the first two weeks of January 2021, cases of COVID-19 more than tripled. So did deaths. At their worst point, more than a quarter-million Americans were testing positive for COVID-19 each day, accompanied by 3,500 deaths. 

The potential for renewed disaster exists. Just 58.9% of Americans are fully vaccinated, and record surges of new cases in Germany, where vaccination rates are 10% higher, show that this isn’t nearly enough to ward off a wave that could once again fill hospitals—and morgues. But with the new ruling, the FDA seeks to end confusion between different authorizations issued over the last month and the handful of states which had already moved to offer boosters for all adults. 

Even before the FDA ruling, many areas have reported that the biggest demand for COVID-19 vaccines isn’t from the unvaccinated. It’s from the fully vaccinated seeking boosters. When the FDA panel of experts met in September, they frustrated many observers by limiting booster shots to those 65 and older or at higher risk of severe COVID-19. Since then, evidence and demand for boosters have increased, and the actions by states to expand booster availability left the nation a patchwork. The new ruling should smooth everything out—if you’re over 18, and it’s been at least six months since you were fully vaccinated, you are eligible for a booster.

With cases increasing, there’s a big reason to promote the use of boosters beyond just protecting those who are already vaccinated. Multiple studies published in September and October indicate that boosters cut the likelihood of being infected and substantially reduce the viral load of those who do become infected. Together, those two effects mean that boosters can lower the chance of someone passing COVID-19 on to others. That makes boosters a critical factor in breaking the chain of community transmission.

While the rise in cases in Germany and elsewhere has led many to claim that vaccines are ineffective in slowing the spread of the virus, it’s worth pointing out that, even with the rapid rise in the last two weeks, the cumulative rate of infections in Germany remains significantly below that in the United States.

Even with the surge of new cases, Germany is doing much better overall than the U.S. or U.K.

What’s clear on this chart is just how badly the U.S. handled the pandemic before any vaccines were available. Before the first jabs rolled out anywhere, the U.S. already saw cases at a much higher level due to the lack of coherent national policy. Those nations that implemented national policies on social distancing and masks quickly moved well ahead of America. And, for the most part, they’ve stayed there.

Every nation suffered a surge last winter. And when the delta variant became dominant, every country saw an increase. But some nations handled these waves of disease much better than others.

The difference between the U.S. and other nations on this chart is the combined effect of vaccination and social distancing policies. Canada, where most provinces have maintained mask mandates and vaccination levels are almost 20% higher than in the U.S., has not only cut its rate of disease drastically, it’s continued to do better even as things south of its border got worse.

At the opposite end of the scale, the U.K. has a vaccination rate almost precisely midway between the U.S. and Canada, but back in June, they dropped nearly all social distancing on what was dubbed “freedom day.” Removing those restrictions immediately drove caseloads in the U.K. upward. Their vaccination rate (67%) is insufficient to stop the community spread of disease, and their removal of restrictions has turned the delta wave into a rising tide where case counts have moved up week over week since spring.

The U.S. needs more people to get vaccinated. It needs the vaccinated to get boosted. And it needs to keep up mask mandates and other social distancing requirements if it hopes to avoid a repeat of last winter.