When the influenza virus causes a global pandemic, it is widely covered in the media and becomes a matter of public concern.  The 2009 H1N1 pandemic is still fresh in our minds, but this virus, which was initially thought to have a high mortality rate, is now treated like a seasonal virus.  

So, what is the mortality rate of seasonal influenza viruses that spread every winter?

 

In this article, the authors investigated the morbidity, hospitalization, and mortality rates of lower respiratory tract infections (bronchitis, pneumonia, etc.), which are often associated with influenza viruses, in all countries and regions of the world. 

The Bill & Melinda Gates Foundation, the philanthropic foundation of Microsoft founder Bill Gates, funded the study.  This kind of study would have required a huge amount of money to collect the global data. 

There were 145,000 deaths from influenza lower respiratory tract infections worldwide in 2017, which means 1.9 deaths per 100,000 population.  In an age-specific analysis, the mortality rate was higher in people older than 70 years, at 16.4 deaths per 100,000 population.  In the analysis by country and region, the mortality rate was higher in Eastern Europe, at 5.2 per 100,000 people.

Data from Japan were also presented, with 7,000 deaths from influenza lower respiratory tract infection, which means 5.1 per 100,000 population.  The mortality rate in Japan is about the same as in Eastern Europe, and much higher than the 1.1 in the US and 2.1 in Western Europe.  In my opinion, probably because of the aging of the Japanese population, severe illness due to influenza are more common among the elderly.

The number of deaths by age from influenza lower respiratory tract infections worldwide, there are peaks in the 0-4 and 80-89 age groups.  As mentioned in the text of the article, it is important to reduce the number of deaths by not transmitting influenza to this age group.  The annual influenza vaccine is partly to protect oneself from contracting the disease, but also to prevent the spread of influenza to infants and the elderly who are more susceptible to severe illness.  This is similar to the idea of giving rubella vaccine to family members who are around pregnant women.

written by the director of the Okino Medical Clinic, a Pulmonologist, M.D., Ph.D.

 

Mortality, morbidity, and hospitalisations due to influenza lower respiratory tract infections, 2017: an analysis for the Global Burden of Disease Study 2017

Lancet Respir Med. 2019 Jan; 7(1): 69–89.

doi: 10.1016/S2213-2600(18)30496-X

 

Summary

Background

Although the burden of influenza is often discussed in the context of historical pandemics and the threat of future pandemics, every year a substantial burden of lower respiratory tract infections (LRTIs) and other respiratory conditions (like chronic obstructive pulmonary disease) are attributable to seasonal influenza. The Global Burden of Disease Study (GBD) 2017 is a systematic scientific effort to quantify the health loss associated with a comprehensive set of diseases and disabilities. In this Article, we focus on LRTIs that can be attributed to influenza.

Methods

We modelled the LRTI incidence, hospitalisations, and mortality attributable to influenza for every country and selected subnational locations by age and year from 1990 to 2017 as part of GBD 2017. We used a counterfactual approach that first estimated the LRTI incidence, hospitalisations, and mortality and then attributed a fraction of those outcomes to influenza.

Findings

Influenza LRTI was responsible for an estimated 145 000 (95% uncertainty interval [UI] 99 000–200 000) deaths among all ages in 2017. The influenza LRTI mortality rate was highest among adults older than 70 years (16·4 deaths per 100 000 [95% UI 11·6–21·9]), and the highest rate among all ages was in eastern Europe (5·2 per 100 000 population [95% UI 3·5–7·2]). We estimated that influenza LRTIs accounted for 9 459 000 (95% UI 3 709 000–22 935 000) hospitalisations due to LRTIs and 81 536 000 hospital days (24 330 000–259 851 000). We estimated that 11·5% (95% UI 10·0–12·9) of LRTI episodes were attributable to influenza, corresponding to 54 481 000 (38 465 000–73 864 000) episodes and 8 172 000 severe episodes (5 000 000–13 296 000).

Interpretation

This comprehensive assessment of the burden of influenza LRTIs shows the substantial annual effect of influenza on global health. Although preparedness planning will be important for potential pandemics, health loss due to seasonal influenza LRTIs should not be overlooked, and vaccine use should be considered. Efforts to improve influenza prevention measures are needed.

Funding

Bill & Melinda Gates Foundation.

Figure