Seasonal Flu Deaths More Common Worldwide Than Expected

Marcia Frellick

December 13, 2017

Between 291,000 and 646,000 people die each year globally from seasonal influenza-related respiratory illnesses, according to new estimates from the Centers for Disease Control and Prevention (CDC) and global health partners.

The new estimates are higher than the previous estimate of 250,000 to 500,000 deaths annually. The estimates were calculated using data from 47 countries between 1999 and 2015, and exclude deaths during pandemics.

Adults aged over 75 years and adults in low-income countries in sub-Saharan Africa and Southeast Asia were hardest hit, note A. Danielle Iuliano, PhD, from the CDC's Influenza Division in Atlanta, Georgia, and colleagues.

"These findings remind us of the seriousness of flu and that flu prevention should really be a global priority," Joe Bresee, MD, associate director for global health in the CDC's Influenza Division and a study coauthor, said in a press release.

Previous mortality estimates for global influenza were calculated more than a decade ago and details on methods were lacking. Now, more countries are able to calculate numbers of deaths from seasonal flu. Additionally, this survey provides age- and country-specific data.

Rates Highest in 75-Plus Group

Authors found average excess mortality rates ranged from 0.1 to 6.4 per 100,000 in people younger than 65 years to 2.9 to 44  per 100,000 for the 65-74 group and 17.9 to 223.5 per 100,000 for those older than 75.

By region, the highest mortality rates were in sub-Saharan Africa (2.8 to 16.5 per 100,000 people) and Southeast Asia (3.5 to 9.2 per 100,000).

In an accompanying comment, Sheena Sullivan, PhD, from the World Health Organization (WHO) Collaborating Centre for Reference and Research on Influenza at the Peter Doherty Institute for Infection and Immunity in Melbourne, Australia, said the statistics by country are particularly useful.

"Often, no mortality estimates are available for low-income and lower-middle-income countries, where limited healthcare infrastructure and the competing demands of other communicable and, increasingly, non-communicable diseases might dominate allocation of health resources," she said.

She notes that the authors recommend wider use of vaccines, but that is more realistic in high-income countries, which are more likely to have influenza vaccination programs and policies in place, she says.

The WHO recommends vaccinating people most susceptible to influenza infection, including older adults.

"However, current influenza vaccines are imperfect and the expected benefits of vaccination programmes might be overstated, especially in elderly people," she writes. She notes that previous modelling has shown that at least some of the reason for the low efficacy of vaccines in the elderly may be due to repeated vaccinations instead of age.

Nonrespiratory Causes Need Study

Dr Sullivan also notes that,  even with the higher estimates, the new study may underestimate the true death toll from influenza because it doesn't include deaths attributable to nonrespiratory causes. The authors also note that those causes need to be investigated because influenza can create or make worse other factors such as cardiovascular disease or diabetes, which are then listed as cause of death on death certificates.

Dr Iuliano and colleagues say that information from the survey can help countries better understand the burden of the infections and importance of detection, prevention, and control.

Dr Sullivan agrees: "The study by Iuliano and colleagues has clearly highlighted the considerable mortality burden associated with seasonal influenza and the need for effective prevention strategies. What is less clear is whether our current prevention strategies are adequate to reduce this burden."

Statistical modeling from data from 33 of the 47countries was used to generate an estimate of deaths for 185 countries across the world. Data from the other 14 countries were used to validate estimates.

Coauthors report grants from the CDC, National Institute of Allergy and Infectious Diseases, the Health and Medical Research Fund of Hong Kong, Harvard Center for Communicable Disease Dynamics, the National Institute of General Medical Sciences, and the University Grants Committee of Hong Kong during the conduct of the study; grants from Sanofi Pasteur and the Foundation for Influenza Epidemiology; and travel expenses paid for by the Global Influenza Initiative and Parexel outside the submitted work.

Dr Sullivan has disclosed no relevant financial relationships.

Lancet. Published online December 13, 2017. Full text, Comment

For more news, join us on Facebook and Twitter


Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.