The swine flu and seasonal flu can coexist during a flu season, but there are a number of differences between them, from how the virus spreads to how long it will be felt in those who contract it; there are also differences how the immune system reacts to them. Perhaps the most important difference is that seasonal flu can be counted on to infect the population at a relatively regular time, but there is no way of knowing when, where or how bad the swine flu will be.
One variety of influenza can be counted on to make yearly rounds throughout the population. Depending on the area, outbreaks of the seasonal flu occur with some kind of regularity; this predictability gives individuals time to be immunized as a preventative measure. When the swine flu suddenly mutated to make the jump from pigs to humans, health organizations were largely unprepared for it, as there was no way to predict the outbreak.
As the seasonal type of flu is so widespread, the human body has been able to develop some forms of antibodies to combat the infection. This immunity is not complete, and individuals usually develop a few days worth of symptoms; those who contract the swine flu, however, are exposed to a virus that has never been in the human population before. As it is a new disease, there are no natural resistances to it, and people are extremely vulnerable to all of the symptoms.
Symptoms of the swine flu and seasonal flu are similar and consist of the same body aches, fever, cough and sore throat. In the swine flu, however, these symptoms are more debilitating; last longer; and can more commonly include gastrointestinal distress, such as nausea, diarrhea and vomiting. Children are more prone to suffering complications from both types of the flu, while the elderly are actually less susceptible to catching severe cases of the swine flu.
There is also a difference in where the swine flu and seasonal flu originate. The virus that causes the seasonal flu is a human one, which means that it circulates mainly through the human population. Swine flu develops in pigs when a single animal contracts more than one type of flu, such as a swine flu and a human flu virus. When these viruses are present in the same animal at the same time, they can undergo a mutation that will allow them to spread through either species. As the swine flu and seasonal flu have such different origins, there are different vaccinations that are available to fight each type of flu.