The CDC Web site says a study has found that no adverse fetal effects have been associated with getting the shot. However, there are both thimerosol-free and preservative-free (which contains trace amounts of thimerosol) versions of the vaccine available -- but you might need to request them from your health-care provider.
Once exposed to a cold or flu virus, there's an incubation period of a few days during which you might not have any outward signs of being sick. However, you can be contagious even before you develop symptoms, which is why you can pass the virus along to others without even realizing it.
Of course, you're most contagious when you have symptoms.
The length of time an infected person can pass along germs also depends on age and health. Younger people and those with weaker immune systems may be contagious for longer periods than healthy adults.
There's no evidence that getting the flu shot increases an older person's chances of Alzheimer's disease, Allen said. "Everything [the ingredients] in the vaccine is there for a reason to make it safer or more effective," he said.
But the link between Alzheimer's and flu shots has been floated on the Internet, all attributed to one physician whose license has since been suspended. This doctor claimed that an individual who had five consecutive flu shots between 1970 and 1980 had a 10 time greater chance of developing Alzheimer's compared with a person who had the vaccine once, twice or not at all. He said this was supposedly because of the mercury and aluminum buildup from these shots, as well as any vaccines received during childhood.
However, the Alzheimer's Association Web site finds no truth to these claims and even cites a study published in the Canadian Medical Association Journal in 2001 that contradicts them. The researchers analyzed data from nearly 4,400 Canadian adults ages 65 and older and concluded that past exposure to vaccines against influenza, polio, diphtheria or tetanus may protect against subsequent development of Alzheimer's.
Influenza viruses can remain viable for up to 24 hours on nonporous surfaces, such as doorknobs, money, phones, light switches and office equipment, Bridges said. "They can survive for only a couple of hours on cloth."
She suggests that because these germs can survive for up to a day on frequently touched and shared surfaces, this provides ample opportunity to pick up these viruses -- and gives you a good reason to wash your hands and keep them away from your face.
Verdict: Usually false
When you have a good match between the circulating virus and the viruses used to make the vaccine, you generally see a 70 percent to 90 percent protection rate or benefit, Bridges said.
But some years the vaccine is not well matched: In 2007, she explained, the flu shot had a 44 percent effectiveness rate because there was an unanticipated drift in one of the circulating strains when the flu vaccine was formulated earlier that year.
But the effectiveness can also vary depending on the age and the health of the person getting the flu shot.