Some say the country should reopen—even if it causes cases to surge—once vulnerable populations are vaccinated. On its face, the curve of COVID-19 infections in Denmark looks reassuring enough. A nationwide lockdown has led numbers to plummet from more than 3000 daily cases in mid-December 2020 to just a few hundred now. But this could be the calm before the storm, as there are two epidemics: one, shrinking fast, that's caused by older variants of SARS-CoV-2, and a smaller, slowly growing outbreak of B.1.1.7, the variant first recognized in England and now driving a big third wave of the pandemic there. If B.1.1.7 keeps spreading at the same pace in Denmark, it will become the dominant variant later this month and cause the overall number of cases to rise again, despite the lockdown. The same is likely happening in many countries, but a massive virus-sequencing effort has allowed Denmark to track the rise of the new COVID-19 variant more closely than any other country.