The cold weather is finally arriving and it’s time to prepare for the flu. Most people us the term “flu” in a very generic sense, meaning anything from cold symptoms to having a case of vomiting and diarrhea.  The “flu” in this column refers to respiratory influenza that kills 36,000 Americans each year and puts another 200,000 in the hospital.

Influenza is caused by a virus and Type A and Type B cause the majority of infections.  Type B typically does not cause severe disease whereas Type A can be lethal, particularly in the young, elderly, and those who have compromised immune systems.

Type A virus can be broken down further into different subtypes or “serotypes” based on which proteins are found on the surface of the virus. When you read about influenza virus with a name like “H3N2,” the “H” and “N” refer to the different proteins on the surface and the numbers refer to the serotype. The serotypes are also often given common names, usually from their region of origin, such as Influenza A “Hong Kong.”

Influenza viruses are constantly changing or mutating slightly so that each flu season brings new serotypes. Scientists make an educated guess each year on what serotypes of virus might occur the following year and formulate that year’s vaccine accordingly.

It appears that the predominant serotype of influenza A this year will be H3N2. This type has a history of causing more severe illness. Unfortunately, this serotype is not in the vaccine this year. That means we can expect a more severe flu season.

While H3N2 is not in this year’s vaccine, it still remains the best defense we have against developing full-blown influenza. It’s also important to attain a high level of vaccination in a community to reduce the spread of the disease to those who are more likely to die from complications of influenza.

It’s important to note that receiving influenza vaccine each fall can’t give you influenza. The vaccine is made up of killed virus particles that can’t cause an infection. Rarely, some people do have a reaction to the vaccine with some fever and aches, but it is not an infection with the virus. Often people are exposed to cold viruses around the time they receive the vaccine. They come down with cold symptoms, and blame the vaccine for “giving them the flu.”

People with egg allergy can still receive the vaccine if they don’t have severe allergic (anaphylactic) reactions to eggs. Those who do have serious egg allergy should receive the vaccine in a doctor’s office or other facility equipped to treat severe reactions.

I also occasionally hear another concern from patients that receiving influenza vaccine will “weaken” their immune systems and they won’t be able to fight the disease when they are exposed to it. Quite the opposite is true – by receiving the vaccine, you are exposing your immune system to the killed virus and your body will be prepared to react quickly to the virus if and when you are exposed to it. Without receiving the vaccine, it takes your body days to produce antibodies to fight off the infection leading to prolonged illness as well as an increased susceptibility to other illnesses like pneumonia.

Symptoms of influenza usually include rapid onset, fever (typically 100-103), dry cough, runny nose, chills, headache and body aches. Most people describe it as being suddenly hit by a truck. This is in contrast to the common cold that usually has a slow onset, low-grade fever (usually 100 or less), cough, runny nose and mild body aches. Both illnesses usually last around ten days.

Since a virus causes influenza, antibiotics are useless. There are anti-viral medications available to shorten the course of influenza, but they must be started in the first 48 hours of illness to be of any benefit. Many people choose not to take the medication since it is expensive, has some side effects and may only shorten the course by a day or two. The medication should be administered to high-risk individuals to help prevent infection if they have a high risk of exposure.

While it’s best to contact your health care provider for advice on whether or not to be seen, most healthy people who develop symptoms of influenza usually do not need to see their doctor and should stay home to avoid spreading the infection. People who should see their physician include those with heart or lung conditions and children under the age of two. Those who have diabetes or weak immune systems should also be seen since they are more likely to develop secondary complications of influenza. Shortness of breath and dehydration with severe weakness are also indications to be seen.

If you get influenza, the best thing to do is stay home, drink plenty of fluids and get as much rest as possible. Over-the-counter cold medications offer some relief and pain relievers can also be helpful if you do not have an allergy or other medical problems that limit your ability to take them. Since this year’s vaccine will have low effectiveness, it becomes even more important to wash your hands frequently to avoid catching the flu or spreading it to others. Alcohol-based hand sanitizers are definitely not as effective as hand washing.

Dr. John Roberts is a local physician. His column appears in Monday’s edition of the Times, and he has a daily health tip on the front page. Dr. Roberts is one of the owners of Sagamore News Media, parent company of The Times.