An invisible wave is possible because cases capture only the number of people who test positive for the virus, which is different from what epidemiologists really want to know: how many people are infected in the general population. That’s always produced an undercount in how many people are actually infected, but the numbers are becoming even more uncertain as government testing sites wind down and at-home testing becomes more common. Unlike during past waves, each household can request up to eight free rapid tests from the federal government, and insurance companies are required to reimburse Americans for the cost of any additional rapid tests they purchase. These changes in testing practices leave even more room for bias.

Sheer pandemic fatigue probably isn’t helping, either. People who are over this virus could be ignoring their symptoms and going about their daily lives, while people who are getting reinfected may be getting milder symptoms that they don’t recognize as COVID, Nuzzo said. “I do believe we are in a situation where there’s more of a surge happening, a larger proportion of which is hidden from the usual sort of sensors that we have to detect them and to appreciate their magnitude,” Denis Nash, an epidemiologist at the City University of New York, told me. He was the only expert I spoke with who suggested that we might be in a wave that we’re missing because of our poor testing data, though he too wavered on that point. “I wish there was a clear answer,” he said.

Instead of relying solely on case counts to gauge the size of a wave, Nash said, it’s better to take into account other metrics such as hospitalizations and wastewater data, to triangulate what’s going on.