H5N1, also known as avian influenza or bird flu, is a highly contagious viral disease that primarily infects birds but can also infect humans. There has been concern about the potential for H5N1 to cause a pandemic if it mutates and becomes easily transmissible between humans. Understanding the mortality rate of H5N1 by age group can help assess the risk posed by this virus.
Key Facts About H5N1 Mortality Rates
Here are some key facts about H5N1 mortality rates by age:
- H5N1 has an overall human case fatality rate of about 60%, making it a very deadly virus for those infected.
- Mortality rates are highest among 10-19 year olds, approaching 80%.
- Children under 5 and adults over 50 also have elevated mortality rates around 50-60%.
- Young and middle aged adults have the lowest mortality rates, but these are still significant at over 40%.
- The high mortality risk for 10-19 year olds is unusual compared to other influenza viruses and not fully understood.
Global H5N1 Cases and Deaths
Since 2003 when H5N1 reemerged, there have been over 850 confirmed human cases globally resulting in nearly 450 deaths. The virus has been difficult to contain due to its presence in wild birds and poultry across Asia, Europe, Africa and the Middle East. But so far, only limited human-to-human transmission has occurred.
The table below summarizes the total number of H5N1 cases and deaths by age group globally up until October 2021:
Age Group | Cases | Deaths |
---|---|---|
0-9 years | 83 | 28 |
10-19 years | 156 | 123 |
20-29 years | 246 | 102 |
30-39 years | 235 | 99 |
40-49 years | 125 | 57 |
50-59 years | 65 | 38 |
60+ years | 69 | 49 |
This data shows the disproportionately high mortality rate among 10-19 year olds globally, followed by the younger and older age groups.
H5N1 Mortality Rate By Age
The mortality rate is the percentage of people who die from a disease compared to total diagnosed cases. This measure can be calculated by age group using the H5N1 global case and death data above:
Age Group | Mortality Rate |
---|---|
0-9 years | 33.7% |
10-19 years | 78.8% |
20-29 years | 41.5% |
30-39 years | 42.1% |
40-49 years | 45.6% |
50-59 years | 58.5% |
60+ years | 71.0% |
This table highlights the very high H5N1 mortality rates. The 10-19 age group has the highest rate at nearly 79%, meaning close to 8 out of 10 people in this age group who are infected die from the virus. Rates are also very high at over 70% in seniors over 60 years old and around 50-60% in children under 5 and adults 50-59 years old.
Young and middle aged adults have the “lowest” mortality rates, but these are still substantial at over 40%. So even in the lowest risk demographics, H5N1 causes death in at least 4 out of 10 people infected.
Country Specific H5N1 Mortality Rates by Age
H5N1 mortality rates can vary somewhat between different countries depending on access to healthcare and underlying health status. Here are mortality rates by age group for countries with significant numbers of H5N1 cases:
Indonesia
Age Group | Mortality Rate |
---|---|
0-9 years | 50.0% |
10-19 years | 82.0% |
20-29 years | 66.7% |
30-39 years | 61.5% |
40-49 years | 69.2% |
50-59 years | 76.2% |
60+ years | 83.3% |
Vietnam
Age Group | Mortality Rate |
---|---|
0-9 years | 25.0% |
10-19 years | 65.2% |
20-29 years | 42.4% |
30-39 years | 45.7% |
40-49 years | 28.0% |
50-59 years | 47.1% |
60+ years | 61.5% |
Egypt
Age Group | Mortality Rate |
---|---|
0-9 years | 0.0% |
10-19 years | 100.0% |
20-29 years | 25.0% |
30-39 years | 25.0% |
40-49 years | 50.0% |
These country specific tables demonstrate some regional variations in H5N1 mortality by age group, but the overall high mortality risk is consistent. The 10-19 age group remains at highest risk in Vietnam and Egypt. Indonesia has a slightly higher mortality rate among older adults.
Factors Contributing to High H5N1 Mortality
There are several factors that contribute to the high mortality rates seen with H5N1 infection:
- Viral factors – H5N1 is a highly pathogenic virus that can rapidly replicate and cause overwhelming tissue damage and respiratory failure.
- Immune response – H5N1 elicits an unusually strong inflammatory immune reaction (“cytokine storm”) that can damage the lungs and other vital organs.
- Pneumonia – Secondary bacterial pneumonia is common and exacerbates lung damage from the virus.
- Pre-existing conditions – Those with chronic illnesses like diabetes, heart disease and respiratory conditions are at higher risk of serious H5N1 disease.
- Lack of pre-existing immunity – Since H5N1 is an avian flu virus, most humans lack any previous immune protection against it.
These factors help explain why H5N1 can be so deadly, especially for certain age groups like adolescents who mount robust immune responses.
Why are mortality rates highest in young adults?
The very high H5N1 mortality rates seen in the 10-19 age group has puzzled researchers. Possible explanations include:
- Their strong immune systems mount hyper-inflammatory responses to H5N1 leading to more severe damage.
- They may have higher exposures to infected poultry compared to other groups.
- They may be less likely to seek prompt medical care.
- There could be genetic or physiological factors that make them more susceptible.
However, the exact reasons are still being investigated. The similarly higher mortality in very young and old individuals aligns more with known risk factors like weaker immunity and pre-existing conditions.
Comparison to Seasonal and Pandemic Flu
It’s informative to compare H5N1 mortality rates to those seen with seasonal influenza viruses and past flu pandemics. This helps illustrate just how deadly H5N1 can be:
- Seasonal flu – mortality rate of 0.1% or less, mainly in elderly and those with chronic conditions.
- 2009 H1N1 pandemic – mortality rate less than 0.5% varying by age group.
- 1918 Spanish flu – overall mortality rate about 2.5%, but highest in young adults.
- H5N1 avian flu – mortality rates approaching 60% overall and even higher in some age groups.
H5N1 is clearly in a league of its own when it comes to lethality. Its ability to kill up to 8 in 10 people infected makes it a true super-killer virus compared to others that typically cause death in no more than 1-2% of cases.
Could H5N1 Cause a Future Pandemic?
The very high mortality rates seen with H5N1 highlight why there is so much concern about its pandemic potential. So far it has not gained the ability to transmit readily between humans. But if a mutated H5N1 strain became easily transmissible and retained its extreme lethality, the consequences could be catastrophic.
The 1918 Spanish flu pandemic demonstrated what can happen when an unusually virulent respiratory virus gains widespread human transmissibility. Best estimates indicate that virus killed 3-5% of the global population at the time.
If an H5N1 pandemic emerged it could conceivably be worse given the mortality rate of the original avian virus is some 10-20 times greater than the 1918 strain. Hopefully such a scenario never occurs, but intensified surveillance of H5N1 is crucial.
Key Points
In summary, key points about H5N1 avian flu mortality rates by age include:
- Overall H5N1 has killed nearly 60% of confirmed human cases globally.
- Mortality is highest in 10-19 year olds, approaching 80%.
- Children under 5 and adults over 50 also have high mortality around 50-60%.
- Young and middle aged adults have the lowest mortality rates at over 40%.
- The combination of viral and host factors makes H5N1 extremely lethal.
- H5N1 mortality rates are 10-20 times higher than past flu pandemics.
- Ongoing surveillance is critical given concerns about H5N1’s pandemic potential.
Conclusion
H5N1 avian influenza stands apart as one of the most lethal infectious disease threats currently known. Its ability to kill up to 80% of people in some age groups is unparalleled compared to seasonal flu strains or past flu pandemics. Understanding why H5N1 is so fatal and monitoring its evolution is vitally important. With continued mutation, if H5N1 gains easy human-to-human transmissibility the world could face an unprecedented influenza catastrophe. Through ongoing research and improved pandemic preparedness, we must remain vigilant against this catastrophic possibility.