Flu season is just around the corner. The first cases of the flu are showing up in the Northern Hemisphere. In fact around 20 million people get the flu each year. About 20,000 people die of complications due to the flu. The flu is caused by a virus called the Influenza virus. There are many different kinds of Influenza viruses that fall into 3 main groups. The groups are called Influenza virus A, B, and C. Group C Influenza virus epidemics are very very rare since this group rarely causes any major problems other than fever, cough, and runny nose. Groups A and B Influenza viruses on the other hand cause major problems every year. These two groups cause high fever, muscle aches and pains, lower back pain, cough, and runny nose. The flu can be so bad you just can’t get out of bed.
Sometimes these viruses can get deep in the lungs and cause pneumonia. Other people get well for a couple of days and then suddenly come down with bacterial pneumonia (secondary bacterial pneumonia). When the Influenza virus gets in the lungs it damages the cells that line the inside surface of the lungs. If the right bacterium gets in these damaged lungs they can cause secondary bacterial pneumonia. Pneumonia can be a life threatening situation. Many people die each year due to pneumonia from the Influenza virus or to secondary bacterial pneumonia. This is especially true for the very young, the elderly, and immunocompromised people (e.g. AIDS patients, chemotherapy patients, asthma patients, diabetes patients, etc.).
To prevent these epidemics we immunize people every year (give them the flu shot). A yearly flu shot is required because the Influenza viruses change so frequently. The common Influenza viruses of last year will not be the common ones we see this year. Therefore every year vaccine manufacturers must make a new vaccine. Influenza viruses can be quite different from each other. Some do not grow very well in the laboratory (they use fertilized eggs to grow the virus). Others grow well but do not make many viruses per egg. As a result some years flu vaccines can be very difficult to make in mass quantities. Last year the United States alone used 76 million doses of the flu vaccine.
This year has been a problem year for the manufacture of the flu vaccine. One of the three Influenza viruses in this year’s vaccine grows very slowly (the Influenza A H3N2 strain). This has caused a delay in supplying the vaccine to health care providers. As a result many places in the U.S. have run out of the vaccine. In our town in Missouri the health department ran