Even before the first horrific phase of the COVID-19 pandemic has run its course, scientists are worried about the second wave of the disease.

It could crash worse than the first, killing tens of thousands of people who did such a good job of sheltering in place they remain virgin ground for the virus. Or it could be a mere swell, with so many people having been infected without symptoms that levels of immunity are higher than realized.

There is no crystal ball to look to, because so many crucial pieces of information remain missing.

Are people who’ve had COVID-19 immune? How long does immunity last? Will the virus play out like influenza and the common cold, peaking during cooler months and falling during warmer ones? Is its deadly path undeterred whatever the weather?

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Until there’s a vaccine “it’s unfortunately not unlikely that we may see a second wave or even a third wave,” said Peter Marks, director of the U.S. Food and Drug Administration’s Center for Biologics Evaluation and Research, which oversees vaccines.

“I shudder to think of that, but I think we have to be realistic.”

Immunity: Can you get the coronavirus more than once?
The first question on every doctor’s mind is whether someone who has had COVID-19 is immune, and if so for how long. People who’ve had mumps are immune from it for life. Versions of the common cold caused by different types of coronavirus see immunity wane within a year. Variations are wide.

COVID-19 is such a new disease that there is no solid data on the immunity of survivors. But given its similarities to coronaviruses such as severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS), it’s expected to convey at least some immunity.

That’s good news because so many people have contracted COVID-19 from SARS-CoV-2, the virus that causes the disease. Many more probably have had it asymptomatically and didn’t know. Both groups likely have some immunity.

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What percentage of the population is immune is impossible to know because the United States doesn’t yet have widespread testing, experts say. An answer is likely months away. Even if immunity isn’t lifelong, the virus may have infected enough people to make it hard for it to find new victims.