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Types of Influenza Pandemic

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A pandemic is a global disease outbreak. A flu pandemic happens when a new influenza virus emerges for which people have little to no immunity, and for which no vaccine exists. An influenza pandemic occurs when a new subtype develops that has not formerly circulated in humans. The disease spreads easily person-to-person, causes serious illness, and can sweep across the country and around the world in very little time. This research explained what Influenza Pandemic means and categorized the three types of influenza, which are Type A, Type B, and Type C Influenza.

The research explained how the next influenza pandemic might arise and its possible outcome. This paper also addressed influenza history which occurred in the years 1918, 1957 and 1968. Moreover, this research used pictures and tables for useful illustrations of relevant information.

Types of Influenza Pandemic

General Discussions

An influenza pandemic is a global epidemic of flu disease that happens when a new form of influenza virus emerges that humans were not previously exposed to (Kilbourne ED. 1975). Kilbourne ED accepts. (1975) that pandemic flu is a worldwide outbreak of disease that takes place as soon as a new influenza virus appears in humans, causes severe illness and then spreads effortlessly from person to person worldwide.

There are three types of influenza. Influenza A, B and C viruses are known to cause disease in humans. While influenza B and C are exclusively human pathogens, influenza Type A viruses are readily isolated from avian species, pigs, and other animals. Influenza Type infections are divided into subtypes based on differences in the surface glycoprotein antigens, hemagglutinin (HA) and neuraminidase (NA). There are 14 known HA subtypes and nine known NA subtypes. All of these subtypes have been isolated in birds, but only three different HA and two different NA subtypes have been isolated in humans (See table below);

Table : Influenza Subtypes

Host HA Subtypes NA subtypes
Humans H1, H2, H3 N1, N2
Birds H1 – H14 N1-N9


The influenza viruses are only one of its kinds amongst the respiratory infections in that they undergo significant antigenic variation (Stuart-Harris C. 1979). Antigenic drift entails small changes in antigen from one season to the next, which can result in the new strain spreading epidemic. The antigenic shift involves significant antigenic changes of the HA and NA molecules and happens merely with Influenza A viruses. These changes will contribute to the emergence of pandemic viruses.

By Stuart-Harris C. (1979), three worldwide outbreaks of influenza occurred in the 20th century: in 1918, 1957, and 1968. Of these, the most serious one was the Spanish Flu of 1918, with 50 million or more deaths worldwide. The last two were in the era of modern virology and most thoroughly characterized. All three have been unofficially identified by the presumed sites of origin as Spanish, Asian, and Hong Kong influenza, respectively. According to Stuart-Harris C. (1979), they are now identified to represent three various antigenic subtypes of influenza Type A virus: H1N1, H2N2, and H3N2, respectively. Not classified as actual pandemics are three prominent epidemics: a pseudo outbreak in 1947 with low death rates, an explosion in 1977 that was a pandemic in children, and A 1976 abortive swine influenza outbreak that had been believed to have a pandemic potential. Large influenza epidemics do not show any predetermined periodicity or sequence, and they all vary. Evidence suggests that real pandemics involving changes in subtypes of hemagglutinin arise through genetic reassortment with Type A viruses of animal influenza.

No one can predict when a pandemic will occur, but experts in public health think it’s only a matter of time before the next one pops up. Experts around the world are looking at the H5N1 avian flu infection in Asia very closely. They are preparing for the probability that the virus may start to spread more quickly and broadly from person to person. If this happens, the next pandemic could begin very soon, or it may take quite a few years for a pandemic flu virus to build up and start spreading worldwide.

Pandemic Influenza May Arise Through at Least Two Mechanisms

Reassortment between an animal influenza virus and a human influenza virus that produces a new virus: a key event would perhaps be a change in the binding specificity of the virus from a receptor in the lower respiratory tract to one in the upper respiratory tract. This may be the outcome of a decrease in at least the initial pathogenicity, as the infection would be more probably, to begin with, tracheal bronchitis rather than pneumonia. Additionally, if human adaptation resulted from reassortment with a human virus, pathogenicity influences on gene segments not in the subsequent reassortment would be absent, and the population would have a degree of prior immunity to the gene segments originating from the human virus, thus further decreasing human pathogenicity.

Direct transmission and adaptation of a virus from animals to humans: pandemic influenza strains Type A virus occur through genetic reassortment between avian and human viruses: pigs may provide for these reassortment events as a mixing vessels. Following the outbreaks of group A subtype H5N1 (A/H5N1) avian influenza viruses in Hong Kong in 1997, in which six people died, the hypothesis was put forward that not only pigs but also humans themselves might serve as mixing vessels for the next pandemic influenza virus. This should also be held in mind that the idea of the mixing vessel is merely a theory, and the portion of pigs as mixing vessels has not been clearly defined. Genetic reassortment of avian and human influenza Type A viruses occurred in Italian Sus scrofa sometime during 1983 and 1985: Human-like strains of H3N2 isolated from 1985 to 1989 contained the internal protein genes of avian-like H1N1 viruses, while those isolated in 1977 and 1983 did not. Multiple genetic reassortments of avian and human influenza Type infections in European Sus scrofa, resulting in the appearance of an H1N2 virus of novel genotype, the evolution of human influenza viruses. Avian-to-human transmission of influenza A virus gene PB1 during the pandemics of 1957 and 1968. The appearance of viruses from Disease A.

Once a contagious virus comes out, its worldwide spread is considered unavoidable. Countries might, through measures such as border closures and travel restrictions, delay the arrival of the virus but cannot stop it. The pandemics of the previous century encircled the globe in 6 to 9 months, even when most international travels were by ship. Given today ‘s speed and amount of international air travel, the virus could spread faster, probably reaching all continents in under three months.


It is complicated to foresee when the next influenza pandemic will take place or how severe it will be. Wherever and whenever an epidemic starts, everybody all over the world is at risk. Countries might, throughout measures such as border closures and travel limitations, delay the appearance of the virus but cannot stop it. Influenza epidemics take place at one to three-year intervals generally in the late fall. Annual inoculations with the current influenza vaccine for that particular year must be administered to all high-risk children and adults as well as health care professionals, where it has been shown to reduce both morbidity and mortality mainly. If physicians were more doing well at vaccinating high-risk individuals, than the current annual 10% rate for children and 40% rate for adults, then people would be much better prepared for the next unpredictable pandemic, which could come as soon. People can get ready, but with the realization that no amount of hand-washing, hand wringing, public education, or gauze masks will do the trick. The keystone of influenza prevention is vaccination. It is irrational to think that people can count on prophylaxis with antiviral agents to guard a large, susceptible population for more than a few days at a time, and that is not long enough. But vaccination against what? People do not know. Maybe against H5N1. But do we not by now have a vaccine? No, we do not; no vaccine of enough antigenic potency is available insufficient supply.

The nature of the next pandemic virus cannot be foreseen, but that it will take place from 1 of the 16 known HA subtypes in avian or mammalian species. Therefore, preparation by genetic reassortment of high-yield seed viruses of all HA subtypes should carry on as soon as possible for potential use in vaccine production.


  • Stuart-Harris C. (1979). Epidemiology of influenza in man. Br Med Bull;35:3–8.
  • Kilbourne ED. (1975). The predictable natural disaster [op. ed.]. New York Times.

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