Seasonal flu kills between 291,000 and 646,000 people worldwide every year, a new analysis of data from 47 countries suggested Wednesday.
The number is higher than a previous estimate of 250,000 to 500,000, according to the study published by the Lancet, which excludes deaths during pandemics.
"These findings remind us of the seriousness of flu and that flu prevention should really be a global priority," Joe Bresee, associate director for global health in the U.S. Centers for Disease Control and Prevention's (CDC) Influenza Division and a study co-author, said in a statement.
In the study, researchers calculated annual seasonal flu-associated respiratory deaths for 33 of those countries, or 57 percent of the world's population, that had death records and seasonal flu 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 worldwide.
Data from the other 14 countries were used to validate the estimates of seasonal flu-associated respiratory death from the statistical models.
Results also showed that the greatest flu mortality burden was in the world's poorest regions and among older adults.
People aged 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.
And despite recommendations from the World Health Organization 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, it said.
The study authors said that these new estimates are limited to flu-associated respiratory deaths and therefore may underestimate the true global impact of seasonal flu.
Flu 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, they noted.