PDC Test - The Signature Features of Influenza Pandemics
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The Signature Features of Influenza Pandemics
By Barbara Johnson
Vast amounts of time and resources are being invested in planning for the next influenza pandemic, and one may indeed have already begun. Data from past pandemics can provide useful insights for current and future planning. Archeo-epidemiologic researchexhibits certain “signature features” of three previous influenza pandemics – A/H1N1 from 1918 through 1919, A/H2N2 from 1957 through 1963, and A/H3N2 from 1968 through 1970 – that should be used as a reference for both national plans for pandemic preparedness and required international collaborations.
Past pandemics were characterized by a shift in the virus subtype, shifts of the highest death rates to younger populations, successive pandemic waves, higher transmissibility than that of seasonal influenza, and differences in impact in different geographic regions. Although influenza pandemics are classically defined by the first of these features, the other four characteristics are frequently not considered in response plans.
Yet the second feature, the shift in mortality toward younger age groups, was the most striking characteristic of the 20th-century pandemics. Exposure to influenza A/H1 subtypes before 1873 may have offered some protection to adults over 45 years of age during the pandemic of 1918 and 1919. A similar mechanism of antigen recycling might explain the partial protection against influenza-related death that was observed among people over 77 years of age during the 1968-1970 pandemic – a possibility supported by the prepandemic presence of antibodies to H3 that were isolated in people born before 1892.
Another possible mechanism is immune potentiation, leading to an increased likelihood of lethal outcomes after influenza infection in specific age groups. Still other hypotheses include the possibility of bacterial superinfection. Although the elderly frequently have the highest death rates during seasonal epidemics, during pandemics the elderly have lowered incidence of death – a fact that has not been generally appreciated or realized. Advance knowledge of which subpopulations are most likely to be at increased risk for death can shape the optimization of control strategies.
The third feature, a pattern of multiple waves, characterized all three 20th-century pandemics, each of which exhibited increased mortality for two to five years.
Increased transmissibility of influenza because of high susceptibility of the population, the fourth feature, has also been documented for all the past pandemics, although the measure of reproductive numbers – a measure of the average number of secondary infections caused by each individual case – vary considerably among studies and pandemics.
The death toll of a future pandemic depends not only on the virulence of the virus in question, but also on the rapidity with which we are able to introduce effective preventive and therapeutic measures. The evidence of multiple waves in the 20th-century pandemics underlines the importance of active, real-time viral surveillance on a global scale. Transnational collaborations are crucial for the effective exchange of genomic, clinical, and epidemiologic data that will make possible the development of vaccines and treatment protocols and the identification of the best population-based strategies. Although our ability to produce a vaccine in sufficient quantities to cover people who are exposed in a first pandemic wave is very limited with today’s technology, an inter-wave period would provide time to increase the production of biomedical tools and to vaccinate populations, thereby mitigating the morbidity and mortality associated with successive and potentially more lethal waves. This is a powerful incentive for international collaboration since all would potentially share the benefits. If an effective vaccine had been available and used even a year after the emergence of the A/H3N2 viruses in 1968, most of the deaths in Europe and Asia could probably have been prevented.
Barbara Johnson of Nutley, N.J., is a participating member in NCRA.
The Signature Features of Influenza Pandemics Quiz
1. A pandemic is
A. A disease confined to the USA only.
B. A disease that originates in China.
C. A disease that spreads worldwide.
D. A disease that originates in elephants.
2. Influenza is a disease of the
D.Mucous membranes of the respiratory tract
3. Twentieth-century pandemics saw a shift in mortality to
B.People born before 1912
C.People with H3 antibodies
D.Younger age groups
4. A mechanism that increases influenza deaths is
C.Virulence of the virus
D.All of the above
5. The elderly may escape infection during an influenza pandemic due to previous exposure to the virus that is causing the particular influenza.
6. There have been three previous influenza pandemics.
7. The A/H1N1 influenza pandemic occurred from 1918 through 1919.
8. During the 1968-1970 pandemic, people over what age had partial protection against influenza-related deaths?
9. A pattern of multiple waves of influenza infection characterized all three 20th-century pandemics, causing increased mortality for 5 to 10 years.
10. The elderly frequently have lower death rates during pandemics because
A.They stay at home more
B.They are more careful not to get exposure
C.They have antibodies to recurrent influenzas
D.They sneeze less often
11. The death toll of a future pandemic depends on how quickly we recognize the symptoms.
12. All three 20th-century pandemics caused mortality for
C.Two to five years
13. It is important to have active viral surveillance for influenza on a global scale. We can then exchange information on
D.All of the above
14. Genomic data regarding influenza pandemics is
A.Genetic makeup fo the causative virus
B.Whether bacteria are also involved
C.Where the virus first occurred
D.The host animal of the virus
15. In 1968, an effective vaccine supplied a year after the emergence of that influenza could have prevented all of the deaths caused by the influenza.
16. The 1968 influenza virus was called
17. The most striking feature of the 20th-century pandemics was
A.The number of people infected
B.The racial makeup of those who died
C.The age of those who died, i.e., younger than previous epidemics
D.The fact that most of those who died were over 60
18. Increased transmissibility of influenza in all past pandemics has been caused by
A.Living in close quarters
B.Poor cleaning habits
C.High susceptibility of the population
D.Virulence of the influenza virus
19. We need to protect ourselves against future pandemics by
A.Creating an injectible vaccine
B.Creating an inhaleable vaccine
C.Administering vaccine to those at risk
D.All of the above
20. More people were killed by the 1918-1919 flu pandemic than were killed in WWI.