The disease infects one group of people first. Infections appear to decrease. And then, infections increase in a different part of the population, resulting in a second wave of infections.

In 1872 the French scientist C.J. Davaine determined through a series of experiments that as a strain of bacteria passes from one host to the next the virulence or strength of the bacteria increases.  This means that even a strain of virus can get so strong as it spreads that very little of it is needed to ultimately kill its host.  This phenomenon is called "passage" and demonstrates that these organisms have the ability to adapt to their environment.  This suggests an adaptation of a virus to man.

So the influenza that infects in the spring and only demonstrates a mild to moderate threat can return in the fall in full catastrophic strength as it passes from host to host becoming stronger. 

According to the CDC An influenza (flu) pandemic is a worldwide outbreak of flu disease that occurs when a new type of influenza virus appears that people have not been exposed to before (or have not been exposed to in a long time). The pandemic virus can cause serious illness because people do not have immunity to the new virus. Pandemics are different from seasonal outbreaks of influenza that we see every year. Seasonal influenza is caused by influenza virus types to which people have already been exposed. Its impact on society is less severe than a pandemic, and influenza vaccines (flu shots and nasal-spray vaccine) are available to help prevent widespread illness from seasonal flu.

Influenza pandemics are different from many of the other major public health and health care threats facing our country and the world. A pandemic will last much longer than most flu outbreaks and may include "waves" of influenza activity that last 6-8 weeks separated by months. The number of health care workers and first responders able to work may be reduced. Public health officials will not know how severe a pandemic will be until it begins.

It is important that we remain vigilant with the very easy steps for prevention including washing hands, covering a cough or sneeze with your hand, not going out in public if running a fever, not coming into contact with sick individuals, eating a healthy diet, adding dietary supplements high in antioxidants to your diet and getting plenty of rest.