This year’s flu season has proven to be the deadliest for children, excluding pandemic years, according to data released on Friday by the Centers for Disease Control and Prevention. About 80 percent of the fatalities were among children who hadn’t been vaccinated.

There have been 172 deaths between October and May, eclipsing the deadly 2012 to 2013 season by one. In previous years, the number has stayed in double digits, with a low of 37. Flu hospitalization records have also edged out previous years, the CDC said.

Unlike previous seasons, reports of the flu stayed high across 50 states.

“This is a feature of this year’s flu—not only did it start early, but it seemed to occur all over the country more or less simultaneously,” Dr. William Schaffner, an infectious disease specialist at Vanderbilt University, told ABC News

The CDC said in a statement that the illness is also lasting longer than usual.

“CDC experts have described the 2017–2018 season as a high severity season, with influenza-like-illness remaining at or above baseline for 19 consecutive weeks, record-breaking flu hospitalization rates, and elevated pneumonia and influenza mortality for 16 weeks,” the CDC said.

While the number has broken records, it’s hardly the deadliest when including pandemic years, during which a new strain of the virus is able to infect people who haven’t developed an immunity. In 2009, the H1N1 pandemic caused 358 pediatric deaths, according to the CDC. The deaths are about evenly split between boys and girls. Half of the children who died already had a previous medical condition that made them highly susceptible to the flu, such as diabetes or asthma.

Every year in the United States, influenza kills between 12,000 and 49,000 people, the CDC has previously reported. Influenza is caused by a virus that attacks mainly the upper respiratory tract—the nose, throat and bronchi, and the lungs—according to a World Health Organization fact sheet.

The infection typically lasts about a week and usually causes high fevers, headaches, general malaise, a sore throat and a cough.

Although vaccines are currently the best method to prevent infection, university researchers have continued to look for other avenues that could decrease morbidity rates in adults and in children. Earlier this week, researchers from Saint Louis University in Missouri announced they have turned a former hotel into “Hotel Influenza,” offering healthy patients $3,500 to infect themselves with the flu and allow doctors to study its progression.

While other universities haven’t attached such an eye-catching name to their programs, it’s not uncommon for universities and other research agencies to offer thousand-dollar paychecks to patients who join influenza research projects.

GettyImages-464478020 A children’s doctor injects a vaccine. The 2018 flu season is now the deadliest on record for children, excluding pandemic years. Sean Gallup/Getty Images