Influenza pandemic
Pandemic = epidemic of worldwide proportions.
- Pandemics are caused by “new” type A influenza viruses
- Pandemic viruses are foreign strains from the animal reservoir (breach of the inter-species barrier, antigenic shift).
- Normal variants of the antigenic drift of the viruses circulate in the human population and cause normal epidemics.
- The largest pandemic of the twentieth century: Spanish influenza (A-H1N1) in 1918-1929.
- The worldwide number of deaths caused by Spanish influenza is estimated at 40 to 50 million; most of them were young people dying due to primary viral pneumonia.
- Other pandemics with milder course:
- 1957 (A-H2N2)
- 1968 (A-H3N2)
- 1977 (A-H1N1)
"Spanish influenza"
In 1918, humanity was struck by a dreadful plague: The first documented cases of this lethal disease of the respiratory tract occurred in the United States in March 1918 and in port towns of France, Spain and Italy in December 1918. People called it “Spanish flu”. Within 10 months, the disease spread over the whole world and then the people who had avoided the first wave were struck by the second one (1918-19) and the third one (1919-20). The death toll was frightening: a new textbook on influenza (1998) specifies 40 to 50 million deaths as realistic values.
The victims of this pandemic were not only elderly and chronically ill persons but especially young healthy adults aged 20-40 years. Clinically, the disease started as a normal flu-like disease (FLD), with sudden appearance of respiratory tract and general symptoms. The majority of patients fully recovered but many developed secondary bacterial pneumonia which could not be treated with antibiotics at that time. What is more, rare primary viral pneumonia caused directly by the virus occurred (for clinical description, see Frame 1).
Primary viral pneumonia during the Spanish influenza epidemic (1918-20)
“Symptoms ... of shortness of breath and occurrence of mahogany spots around the lips which broadened and merged together into violet cyanosis until a white man could not be distinguished from a coloured one were visible.” Characteristic odour was emitted by many patients. When cyanosis increased, patients started to catch breath; bloody foam emerged from their mouth; they started to be delirious, and death occurred by asphyxiation: with rigor mortis. Bloody liquid suddenly flowed out from the mouth and the nose. The time between hospital admission and death ranged from several hours to 2-3 days.”
(from Potter CW: Chronicle of Influenza Pandemics, in: Textbook of Influenza (Nicholson KG, Webster RG, Hay AJ eds.) Oxford 1998, p. 9)
In 1918, antigenic shift occurred because foreign strains from the animal reservoir broke the inter-species barrier and infected people causing a pandemic.
Despite numerous studies, a new pandemic cannot be exactly foreseen. We should be prepared that an entirely new virus may appear at any moment.
As it is visible in the figure, the A-H1N1 subtype totally disappeared when subtype A-H2N2 appeared in 1957, similarly as subtype A-H2N2 in 1968 disappeared after the A-H3N2 subtype appeared. In 1977, the A-H1N1 virus subtype which was closely related to the viruses circulating in 1947 and 1956 reappeared in the population (Russian influenza) without replacing the circulating "drift" variant of the A-H3N2 subtype. In 2001, both "drift" variants of two different subtypes of the influenza virus (A-H1N1 and A-H3N2) circulate. These two subtypes of virus A are contained in the currently recommended influenza vaccines.
"Asian influenza"
In 1997, the avian A-H5N1 virus appeared in hens in Hong Kong. This virus was transmitted directly to 18 persons in the age of 1 year to 60 years; six of them died. Doctors and healthcare authorities all over the world were extremely worried. Fortunately, the virus could not be transmitted from a human to a human. The healthcare authorities in Hong Kong decided to destroy all geese and hens in that area (millions of animals). After this action, no new cases in humans occurred.
Cumulative Number of Confirmed Human Cases of Avian InfluenzaA/(H5N1), based on the WHO report of 23August 2006
| Country | 2003 | 2004 | 2005 | 2006 | Total | |||||
| patients | deaths | patients | deaths | patients | deaths | patients | deaths | patients | deaths | |
| Azerbaijan | 0 | 0 | 0 | 0 | 0 | 0 | 8 | 5 | 8 | 5 |
| Cambodia | 0 | 0 | 0 | 0 | 4 | 4 | 2 | 2 | 6 | 6 |
| Chine | 1 | 1 | 0 | 0 | 8 | 5 | 12 | 8 | 21 | 14 |
| Djibouti | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 1 | 0 |
| Egypt | 0 | 0 | 0 | 0 | 0 | 0 | 15 | 7 | 15 | 7 |
| Indonesia | 0 | 0 | 0 | 0 | 19 | 12 | 55 | 44 | 74 | 57 |
| Iraq | 0 | 0 | 0 | 0 | 0 | 0 | 3 | 2 | 3 | 2 |
| Thailand | 0 | 0 | 17 | 12 | 5 | 2 | 3 | 3 | 25 | 17 |
| Turkey | 0 | 0 | 0 | 0 | 0 | 0 | 12 | 4 | 12 | 4 |
| Vietnam | 3 | 3 | 29 | 20 | 61 | 19 | 0 | 0 | 93 | 42 |
| Total | 4 | 4 | 46 | 32 | 97 | 42 | 111 | 75 | 258 | 154 |
