Even if a swine flu vaccine isn't available, publicity over the worldwide outbreak probably will prompt more Americans to get the regular seasonal flu vaccination this fall, health officials say.
But it's also likely to stir up old fears and new controversies over the vaccine's effectiveness and safety.
The Centers for Disease Control and Prevention says the vaccine is the best way to reduce your chances of getting seasonal flu, which kills 36,000 Americans a year.
But vaccine opponents note that unlike vaccines for mumps and measles, the flu shot must be reformulated every year and doesn't always match the strains that end up circulating. Some claim preservatives in the vaccine are dangerous, though scientific studies consistently say they are not a threat.
And some wonder why most doctors don't get vaccinated.
Why get a flu shot?
The research on how well the flu vaccine works is mixed. A 2007 study in the New England Journal of Medicine found that flu vaccination significantly reduced the risk of hospitalization for flu and pneumonia among people 65 and over.
Another study, published last year in the Archives of Pediatrics & Adolescent Medicine, found that over two recent flu seasons, vaccinating children ages 5 and younger did not reduce hospitalizations or doctor visits linked to the flu.
Americans are divided, too. More than 100 million get the annual flu shot, which means nearly 200 million do not. A survey by the RAND Corp. last December outlined the main reasons Americans don't get the vaccine: 25 percent feel they don't need it, 20 percent don't believe in it and 19 percent think they might get sick or experience side effects from it.
The ongoing swine flu epidemic, which has struck more than 11,000 people in 42 countries, probably will win converts to vaccination.
"I think that would be a good bet," said Dr. Carolyn Bridges, an associate director of epidemiologic science at the CDC. "I do anticipate that we'll have more interest this year in prevention of seasonal influenza."
'A long way to go'
The CDC says that anyone over 6 months of age can get vaccinated, but it recommends vaccination for children ages 6 months to 18 years, adults 50 and over, pregnant women, people with chronic medical conditions such as asthma, and doctors and other health care workers.
All of the target groups together represent 85.4 percent of the U.S. population, or 261.5 million.
Only about 40 percent of the targeted population gets vaccinated each year. That includes about a third of children and a little more than half of people 50 and over.
Less than half of doctors and other health care workers get the vaccine, an indication many of them have the same concerns and objections about the vaccine as the public does.
"We haven't gotten to the point where I think any of us in public health have been satisfied with the kind of vaccination rates that we've achieved thus far," Bridges said. "We have a long way to go to make sure that all those people at risk of complications are as protected as they can be."
Complicating that mission has been the controversy over ingredients used to stabilize vaccines. Activists such as actor Jenny McCarthy, whose son is autistic, have claimed thimerosal, a mercury-based preservative, leads to autism and Alzheimer's disease. Such campaigns, public health experts say, have reduced overall childhood vaccination rates.
But health officials say there is no convincing evidence that the small amount of thimerosal in some vaccines causes any harm. "We believe this is a safe ingredient," said Dr. Anne Schuchat, the CDC's interim deputy director for science and public health.
History gives vaccine opponents plenty of ammunition that vaccine supporters can't entirely refute.
In February 2008, the height of flu season, the CDC announced that the seasonal flu vaccine was not well-matched to the strains of flu that were circulating. Each year, researchers study the circulating flu strains and select three judged most likely to cause illness the following season to be included in the vaccine.
It's an inexact science.
"Every year we keep our fingers crossed to see how well the prediction will work," Schuchat said. "Some years it works very well, and some years it doesn't work as well."
Schuchat acknowledged other limitations. She said the vaccine works best in people with strong immune systems, but not as well with the elderly and people with weaker immune systems — the ones who need it most.
The current swine flu epidemic has been a powerful reminder of the swine flu scare of 1976, when the vaccine actually killed more people than the virus itself.
The government abruptly suspended its vaccination effort when the vaccine was found to have caused hundreds of cases of Guillain-Barre syndrome, a disease in which the body damages its own nerve cells, resulting in muscle weakness and sometimes paralysis.
The CDC says flu vaccines produced since 1976 have significantly lower risk of GBS, citing one study that put the chances at one-in-a-million.
That's not much comfort if you're the one. And odds aside, some opponents ask how many other vaccine recipients might suffer from symptoms that are never properly diagnosed.
"It's just not realistic to think that the ingredients in a flu shot can cause severe neurological damage in a small percentage of the population while leaving everyone else completely uninjured," Dr. Ben Kim, a Canadian chiropractor and acupuncturist, wrote on his Web site.
"Even if the odds were 1-in-300-million, I would still say no to getting a flu shot — why take any risk of creating serious damage to my body?"
But there's no more serious damage to your body than death. That seems to be the feeling of federal officials, who plan to launch a "full and aggressive" vaccine campaign to urge all Americans to get a flu shot.
"We tend to forget that seasonal influenza can be quite severe," said the CDC's Bridges.
Richard Martin can be reached at firstname.lastname@example.org or (727) 893-8330