How does the Swine Flu disappear?

Answer 1

It has not disappeared yet, although the pandemic has been declared over. There are still isolated outbreaks around in the world, and it is expected to be one of the main viruses for our present flu season (2011-2012) in the US and Northern Hemisphere. The vaccine is included in the 2011-2012 seasonal flu vaccine. There were some confirmed cases of H1N1/09 during the summer months in the US and other nations, including the Southern Hemisphere. They were very rare in the US in the summer.

As the weather changes seasons influenza viruses do not infect people as well for some reason, not fully understood. Perhaps changes in humidity or the temperatures. That is why we have a flu season in the Northern Hemisphere each Fall and Winter. The Southern Hemisphere has their season in their Fall and Winter (which is our Spring and Summer time). In between seasons, the flu viruses are quiet/dormant/inactive and not spreading as much.

Influenza viruses also die out when there is no host, which they need to be able to replicate. As more and more people are vaccinated for this type of Swine Flu (H1N1/09), the viruses' ability to find hosts who do not have immunity is markedly reduced. Smallpox was eliminated because of an effective vaccination program. Swine flu could possibly also be eliminated if everyone who could would get their vaccinations.

However, influenza viruses can usually mutate easily and quickly. When they mutate, they can sometimes get around our immunity from the vaccination, since the antibodies we made against them from the vaccination is no longer effective for the new mutated virus (they "don't fit" any more). This can be a good thing and the actual swine flu can totally be changed into the new form, eliminating the original form from the wild. If the new form is incapable of making us sick for another reason, or causes only very mild symptoms that may go unnoticed, it would be effectively eliminated and disappear. More often, however, they mutate into forms that cause similar illness but no longer are susceptible to our defenses.