Omicron, the highly contagious variant of the coronavirus, is causing a sharp spike in cases in Brazil after a long respite, even if official data is failing to reflect the toll of the new wave.

Private diagnostics companies such as Grupo Fleury SA and Diagnosticos da America SA have seen positivity rates skyrocket to as much as 40% in January, up from less than 5% just a month ago. The demand for tests is surging, with emergency rooms in cities such as Sao Paulo and Brasilia packed with people reporting flu-like symptoms. In Rio de Janeiro, daily infections passed 1,200 on Jan. 1, up from about 90 a month before.

On Thursday, Brazil reported 35,826 new cases, the highest daily toll in about three months. While it’s a fraction of the more than 100,000 it registered at the height of the pandemic in mid-2021, the real numbers are likely far greater, according to health experts. That’s because the system used by states, municipalities and private labs to report cases to the federal government has been mostly down since a cyberattack in December.