The Imperfect Science of Mapping the Flu

By the second week of January, the Centers for Disease Control and Prevention thought this flu season had already peaked. Cases of the disease were widespread around the country, but the overall numbers were not overwhelming: The hospitalization rate was about half as high as in 2014-15, the last severe flu season. CDC officials predicted there would be fewer deaths.

But the feverish masses kept growing. Now, for the third week in a row, flu activity remains widespread in 49 states, according to the latest CDC data. Some 6.6 percent of patients visiting the doctor now have flu-like symptoms, the highest rate since 2009. And the rate of pneumonia and influenza-related deaths has suddenly rocketed up. This year’s death rate is now on pace to match or exceed that of 2014-15.