The adenoviruses are responsible for the common cold. There are so many different types of cold viruses that it has been impossible to develop an effective immunization for the common cold. One strain (A14) has caused some concern because it has mutated to become a very serious variety. Several people over the last couple of years have actually died from complications. But this type has remained quite rare and usually happened in people with other medical problems. It is not expected to become widespread. 

The flu is a viral illness caused by the Influenza virus, and spread by contact from person to person or by inhaling infectious droplets from someone else with the flu. There are several types of influenza viruses, Type A, B, & C. Type A is most common and leads to more serious epidemics. Type B is usually a milder type, and Type C is even milder, similar to symptoms of the common cold. The sudden onset of headache, chills, generalized muscle aches occur at first. Then respiratory symptoms like congestion, cough and sore throat can appear. These symptoms are usually accompanied by fever between 100 to 103 degrees in adults, but may be even higher in children. Usually gastrointestinal symptoms of nausea, vomiting and diarrhea do not ordinarily appear with the flu, but may be signs an symptoms of other viruses, commonly called the "stomach flu" 

It is a common misconception that cold weather causes the flu. It doesn't. But it may play some role if you are in a state of lowered resistance. Stress, chronic illnesses, and cancer are some known causes of lowered resistance. The immune system is very complex, however, and we don't know all the causes. 

Either inhaling or touching infected particles and airborne droplets is how these viruses usually spread. So here's some tips on things that will help cut down the spread of these viruses from person to person.