For a lot of people, however, the vaccine shortage doesn't matter. Despite urging from health officials and doctors, many people refuse to get their flu vaccines, even when they're free and plentiful. They're suspicious that they'll catch the flu or some other illness from the shots.
In New York City, for example, about 30 percent of patients who are offered the shot refuse it, recent surveys show. And only 45 percent of blacks over 65 were vaccinated in 2004, compared with 55 percent of whites, according to the Centers for Disease Control and Prevention.
"There are some groups that are resistant to vaccination because of the belief that influenza shot causes the flu," says Curtis Allen, a CDC spokesperson. "It doesn't."
Health officials urge everyone over 6 months of age to get vaccinated, especially the elderly and people with chronic medical conditions. Yet overall, only an estimated 5 percent to 20 percent of Americans line up for the shots each year, the CDC reports.
"You have all these individuals who are high risk who don’t get their immunizations because they’re listening to these urban legends," says Dr. Georges C. Benjamin, executive director of the American Public Health Association.
Unlike some vaccines that contain live viruses and can sometimes cause major symptoms of the illness, flu shots contain inactivated, killed viruses.
Confusing other viruses with the flu
Most people get no reaction from immunization, although some get a mild fever or rash near the injection area. People who are allergic to eggs should avoid the vaccine.
Dr. Brian Currie, vice president and senior medical director of New York's Montefiore Medical Center, says some of the distrust comes from years when the influenza strain included in the vaccine wasn't a good match to the circulating strain and many people who were vaccinated got sick anyway.
Because it takes six months to grow the vaccine in eggs, officials from the World Health Organization try to identify which strains of the always mutating influenza virus will be active the following winter. In the 2003 flu season experts failed to include the Fujian strain, leading to an outbreak that hit children under 5 especially hard.
There are also many other non-flu viral strains that pop up during the winter months that are often mistaken for the flu.
"Someone gets vaccinated and a short time later they get a different virus and they tend to associate that illness with their prior vaccination," says Currie. "They confuse the other viral infection with the flu."
Many mistake the common cold with influenza as well. A cold may build slowly, but the flu comes on abruptly with high fever, total body malaise, and aches and pain. The flu doesn't typically involve nausea, vomiting or diarrhea.
"With the flu, basically you're bed-bound," says Currie.
Because it takes two weeks for antibodies to develop that protect against influenza infection, it's not unusual for someone to get the shot and then suddenly come down with the flu because of prior exposure, he says.
Distrust of the flu vaccine also can be traced back to the 1976 outbreak of "swine flu" when there were several hundred cases of Guillain-Barré Syndrome, a rare autoimmune disorder usually associated with bacterial or viral infections, that occurred in vaccinated adults. The vaccination program was ended.
While the majority of studies found no link between the vaccine and GBS, health officials couldn't rule out a connection.
The flu vaccine has also been linked to neurological disorders such as multiple sclerosis, although a 2003 report from the Institute of Medicine dismissed evidence linking the flu vaccine to MS.
The manufacturing process is "purer" now, says Allen, making vaccines today safer and more effective.
Increasingly, some parents refuse to get flu vaccines for their children because some doses contain mercury, a preservative they fear could cause autism.
Mercury-free pediatric flu shots are available, although because only one manufacturer markets them, they can be difficult to find, doctors say.
Are more people lining up for their flu shots this year because of fears over avian flu (the regular flu vaccine doesn't protect against bird flu) or increased awareness because of last year's shortage scare?
It's too soon to say. It's also too early to predict whether a slow start to this year's flu season means it'll be a mild one. The flu season usually runs from late October through March, peaking sometime in January.
"Anyone who wishes to avoid the flu, we would recommend getting vaccinated," says Allen.