According to new estimates published today, between 291,000 and 646,000 people worldwide die from seasonal influenza-related respiratory illnesses each year, higher than a previous estimate of 250,000 to 500,000 and based on a robust, multinational survey.

The new estimate, from a collaborative study by CDC and global health partners, appears today in The Lancet. The estimate excludes deaths during pandemics.

“These findings remind us of the seriousness of flu and that flu prevention should really be a global priority,” says Joe Bresee, M.D., associate director for global health in CDC’s Influenza Division and a study co-author.

The new estimates use more recent data, taken from a larger and more diverse group of countries than previous estimates. Forty-seven countries contributed to this effort. Researchers calculated annual seasonal influenza-associated respiratory deaths for 33 of those countries (57 percent of the world’s population) that had death records and seasonal influenza surveillance information for a minimum of four years between 1999 and 2015. Statistical modeling with those results was used to generate an estimate of the number of flu-associated respiratory deaths for 185 countries across the world. Data from the other 14 countries were used to validate the estimates of seasonal influenza-associated respiratory death from the statistical models.

Poorest nations, older adults hit hardest by flu

Researchers calculated region-specific estimates and age-specific mortality estimates for people younger than 65 years, people 65-74 years, and people 75 years and older. The greatest flu mortality burden was seen in the world’s poorest regions and among older adults. People age 75 years and older and people living in sub-Saharan African countries experienced the highest rates of flu-associated respiratory deaths. Eastern Mediterranean and Southeast Asian countries had slightly lower but still high rates of flu-associated respiratory deaths.

Despite World Health Organization recommendations to use flu vaccination to help protect people in high-risk populations, few developing countries have seasonal flu vaccination programs or the capacity to produce and distribute seasonal or pandemic vaccines.

Global flu surveillance protects all nations, including U.S.

CDC works with global partners to improve worldwide capacity for influenza prevention and control. CDC has helped more than 60 countries build surveillance and laboratory capacity to rapidly detect and respond to influenza threats, including viruses with the potential to cause global pandemics.  These efforts, along with technical support, has helped some partners generate estimates of influenza-associated deaths, which contributed to this global effort.

Global surveillance also provides the foundation for selecting the viruses used to make seasonal flu vaccines each year. This helps improve the effectiveness of flu vaccines used in the United States. Global surveillance also is crucial to pandemic preparedness by identifying viruses overseas that might pose a human health risk to people in the United States.

“This work adds to a growing global understanding of the burden of influenza and populations at highest risk,” says CDC researcher Danielle Iuliano, lead author of The Lancet study. “It builds the evidence base for influenza vaccination programs in other countries.”

The study authors note that these new estimates are limited to flu-associated respiratory deaths and therefore may underestimate the true global impact of seasonal influenza. Influenza infection can create or exacerbate other health factors which are then listed as the cause of death on death certificates, for example cardiovascular disease, diabetes, or related complications. Additional research to estimate non-respiratory causes of flu-associated deaths are ongoing.