How many people will be so immune that they will never get swine flu?

Answer 1

It was originally thought by the World Health Organization (WHO) and other infectious disease research entities that few to none would be naturally immune to Novel H1N1 influenza since there had not been a previous strain of flu virus like it before. It is unique because it has genetic components from three species: pigs, birds, and humans, unlike any prior known influenza strains. This is the reason that it was thought that it had this potential to be worse than other Type A H1N1 flu virus strains that humans can get.

When there have not been strains similar in the past, there is no immunity from hereditary sources or from prior vaccinations or exposure. It is totally new, so people would have much more trouble with it than with the typical seasonal flu viruses that have been around for hundreds and thousands of years. However, an unusual trend was noticed during the initial pandemic spread through the North American countries, which was that the group typically most at risk of catching and dying from influenza, the population group aged 65 and older, did not see the typical severe disease and death rates as with even seasonal flu.

It is not entirely known why, but it is suggested that it could be because the earlier strains of Swine Flu that spread initially to humans in the 1930's, although only containing genetic material from pigs and humans, was close enough to the current Novel H1N1 that the past exposure to it is providing some degree of immunity to those who were around back then.

It is still unknown if that will be true for that demographic group in the other areas of the world as the virus spreads in the pandemic, or if it was only applicable in the US. There is also always the possibility that a virus will mutate during a pandemic and then have different groups who may or may not have any resistance. Some people who have been exposed to or have contracted the 2009 Novel H1N1 have had very mild symptoms of a mild cold, so although they were not immune, they still had milder cases of the flu.

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