What felt like a miserable flu season this past year was, in fact, a miserable flu season.
The 2017–2018 influenza season was classified in the “high severity” category overall, according to a new report from the U.S. Centers for Disease Control and Prevention. It was only the third use of this designation since 2003.
To assess how the influenza virus has been affecting U.S. communities, the CDC applied a new method of evaluating severity to every annual outbreak back to the 2003–2004 season. The evaluation considers the percentage of flu-related visits to outpatient clinics, rates of hospitalizations and the percentage of deaths linked to flu or pneumonia.
The most recent flu season was among the worst for hospitalizations, the report finds, with the highest hospitalization rate for all ages combined since 2005–2006.
It was also a bad year for flu-related deaths among children, with 171 fatalities counted as of June 1, making it one of the deadliest in recent years. Only 22 percent of child victims who were eligible for the flu vaccine for the 2017–2018 season actually got vaccinated before becoming ill, researchers write in the June 8 Morbidity and Mortality Weekly Report.
Last season’s flu vaccine was about 36 percent effective overall, but only 25 percent against the predominant viruses from the H3N2 subtype of influenza A. However, even in years of low effectiveness, the flu vaccine is still the best protection against the illness, the CDC says (SN: 10/28/17, p. 18). The agency has yet to release estimates on how many illnesses were avoided this season because of vaccine use, but says vaccination prevented an estimated 5.29 million illnesses during the 2016–2017 season.
Only three flu seasons, including 2017–2018, rank in the overall “high severity” category since 2003, based on a CDC assessment of flu-related visits to outpatient clinics, hospitalizations and flu or pneumonia deaths.