After a long plateau that for a time looked like the start of a fourth surge, coronavirus infections are finally declining in the United States. More than half of adults have received at least one dose of the vaccine, and adolescents 12 to 15 years old may be able to get inoculated as soon as next week. As Americans resume many aspects of pre-pandemic life, there is a sense that the worst is behind us.

I share this optimism, but I also worry about what could be in store for us after a relatively calm summer.

Here’s what I project will happen over the next several months: Vaccinations are already slowing, but I believe there is a good chance that President Biden will meet his new target of administering at least one shot to 70 percent of adults by July 4. Add the numbers of inoculated teenagers, as well as those who have recovered from the coronavirus, and we could come close to 70 percent of the total population who have some immunity to covid-19.

It’s not clear that this level will be enough to reach true herd immunity and stop the virus in its tracks entirely. But even without herd immunity, we will see a major decline in infection. Israel, with an estimated 68 percent of its population with antibodies either from vaccination or recovery, has experienced a dramatic decline in cases, from around 10,000 daily new infections at its peak to now fewer than 100.

The United States will likely follow suit. Warm weather will help, too, and the infection rate could drop so low that most remaining restrictions will be lifted. I imagine that weddings will soon take place as they once did, complete with indoor receptions and dancing, and so will in-person conferences, full-capacity worship services and sports games. All K-12 schools and universities should be able to reopen fully in the fall. More and more employees will be asked to return to worksites. Outdoor masks will become a rarity, and indoor mask mandates will probably be lifted, too.

After more than a year of pandemic constraints, this return to normal will be very welcome. From a public health standpoint, we finally have a chance to suppress infections low enough that we can move from the blunt application of mitigation measures to the targeted tools of containment. New cases could be detected as they occur; people exposed could be quarantined; and chains of transmission could be halted. Some outbreaks will still occur, especially in communities with low levels of vaccination, but these will be infrequent enough that national resources can be diverted to specific regions as hot spots emerge. Some people will still become ill but not at the numbers that threaten to overwhelm hospitals.

There’s a downside to this otherwise rosy picture: Those on the fence about vaccination will have even less reason to get inoculated. People who thought covid-19 was overblown will feel more validated in their thinking, and it will be even harder to persuade them about the extraordinary benefit of the vaccine. A quiescent summer also means fewer compelling arguments for businesses and schools to mandate vaccines. If virtually all restrictions are lifted and the unvaccinated can move about society just as the vaccinated do, we may never reach the herd immunity threshold needed to eradicate the virus.

Then, come fall and winter, the United States could be in big trouble again. Coronaviruses are winter respiratory viruses. There could be a resurgence with colder weather and as people spend more time indoors. More contagious and deadlier strains could arise in other countries and quickly spread to ours. Communities with large proportions of unvaccinated people could be tinderboxes for these new strains. Existing vaccines will probably protect against most variants, but there could be exceptions. Booster shots can be developed to target these mutants, but the uptake of the booster is almost certain to be far lower than of the initial vaccine.

The result? We could see the comeback of covid-19 in the winter of 2021. The unvaccinated would be at the highest risk, but even those who received the vaccine could become ill with new variants. If enough cases develop and hot spots emerge, the United States won’t be able to contain the virus and may have to resort again to societal-level restrictions.

The potential of a calamitous winter doesn’t mean we need to remain in self-imposed lockdown now. In fact, I encourage everyone who is vaccinated to return to as much of pre-pandemic normal as they feel comfortable. This summer is the time to travel, reunite with family, and enjoy restaurants and nightclubs again. But if we want the freedom of the summer to last, we need to do everything we can to get far more Americans vaccinated. We’ve already experienced the catastrophe brought on by covid-19; now we must prevent it from occurring all over again.

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