Oct. 28, 2008 -- Perhaps because most of us have had firsthand experience with colds and flu, there's no shortage of misconceptions and old wives' tales that get passed along about them.
But simply because we're well acquainted with these familiar bugs -- and have come to expect getting the sniffles or a scratchy throat when the weather turns nippy -- it doesn't mean that we're always well informed about how to prevent or treat them.
In fact, many people remain unclear on the exact difference between a cold and the flu. While the lines are often blurred by preconceived notions, colds are known to be pretty common occurrences in adults and children every year. The flu, on the other hand, happens less frequently and affects 5 percent to 20 percent of Americans annually, according to the Centers for Disease Control and Prevention.
So, do you think you're up to date on your cold and flu knowledge? We've run some common cold and flu myths by the experts and asked them to set the record straight. See if you can spot the truth from the false statements below.
There's no need to get a flu shot after November because it won't do you much good.
Although most people get vaccinated between October and November, it's not too late to get a flu shot in December, January and February, said Curtis Allen, a CDC spokesman for the national immunization program. In most years, he said, influenza peaks in February or later, and it takes about two weeks for the vaccine to become effective.
Allen said that most people probably get vaccinated before the end of November because afterward they start thinking about the holidays. And some of the retail stores or pharmacies with flu clinics might shut them down by early December to free up space for holiday shopping.
Allen noted that December or beyond is still a good time to get your flu shot because many people are traveling, out of school or on vacation, and they may come in close contact with others who have the flu and then bring it home with them. The flu shot can still be protective whether you get it in October or February.
If you catch a cold, it means your immune system is weak.
"Anybody with a healthy immune system can develop a cold or the flu," said Dr. Erica Brownfield, an associate professor of medicine at Emory University School of Medicine in Atlanta. Coming down with a cold means that you've been exposed to the virus -- which enters your body through the nose, mouth or eyes -- and that your immune system wasn't successful at resisting the infection.
More than 200 viruses (mainly the rhinovirus) can cause the common cold, and your immune system may not yet have built up resistance to the one you came in contact with. That doesn't mean it's falling down on the job.
"But if your immune system is weak, you're at higher risk of developing more serious consequences if you do get sick," Brownfield said.
The "stomach flu" is caused by the same virus that causes influenza.
"The stomach flu is not caused by the influenza virus," Brownfield said. The two ailments are caused by two different, non-related viruses.
Although many people use the term "stomach flu" to describe an illness that includes nausea, vomiting, stomach pain or diarrhea, it's actually not a true medical diagnosis. The actual name for this condition is gastroenteritis and this irritation or inflammation in the gastrointestinal tract might be caused by a virus or by bacteria or parasites.
Influenza is a respiratory disease, not a gastrointestinal disorder. Sometimes children and in rarer instances adults with the flu might feel sick to their stomachs, but it's not a typical flu symptom the way fever, congestion, fatigue and muscle aches are.
It's OK to have sex with someone who has a cold or the flu, as long as you don't kiss them.
Verdict: Probably true
Having sexual contact with someone doesn't put you at risk for cold or flu, Brownfield said. Kissing someone on the mouth might spread germs, but the same could be said if you shook a person's hand or planted a smooch on a person's cheek when they had a runny nose.
Because viruses get transmitted both in the air and through direct contact, a good rule of thumb is to not get too close to people with a cold or the flu to protect yourself from coughs and sneezes.
As for giving a loved one a kiss when they're sick, Brownfield said, "I'd take the risk."
If you get the flu once, you won't get it again that season.
In any given year, there's more than one type of influenza virus that might be circulating, said Dr. Carolyn Bridges, associate director for science in the influenza division of the CDC.
Once you've had the flu, you develop antibody protection to the viral strain that caused it. But infection with one type of influenza strain will not safeguard you against any new or mutated or different viral strains.
And because each flu season is unique, the vaccine gets formulated annually based on the influenza strains projected to be circulating.
You should skip the flu shot if you're pregnant.
Women who are pregnant are at increased risk of complications and hospitalizations from the flu, which is why the vaccine has been recommended for pregnant women, said Bridges.
She said there are three important reasons why she would urge pregnant women to get the flu shot: First is because they are at increased risk for complications from flu. A second is that women can pass along preventive antibodies to their babies, who can't get vaccinated during their first six months of life. And third is to help women avoid a high fever during pregnancy, which may lead to congenital illnesses in their offspring.
Getting the vaccine is safe during any trimester of pregnancy, said Curtis Allen from the CDC. "Influenza is more dangerous to the mother and child than any indication of the vaccine."
Even so, Allen said that he realizes that many mothers-to-be are concerned about what they put into their bodies, and that includes deciding whether or not to get the shot. Maybe that's why only 12 percent to 14 percent of pregnant women typically get a flu shot, even though all are advised to do so.
The low vaccination rates among pregnant women could stem from concerns over the safety of the mercury-containing compound thimerosol, which is used as a preservative in the shot.
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.
When you have a cold, you're contagious even when you have no symptoms.
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.
Older adults who get the flu shot increase their risk of Alzheimer's disease.
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.
Flu viruses can survive for a couple of hours on the surfaces of doorknobs, money, phones, light switches and office equipment.
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.
The flu shot is only about 60 percent effective.
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.
Younger, healthier people tend to have higher rates of protection from the vaccine because they have a higher antibody response to it. As you get older, your immune system is not as efficient as it once was and it's less likely to give as strong an immune response.
Also, Bridges says that in years when the flu vaccine is a strong match, the effectiveness rates for it in older adults and in those who are immunocompromised is closer to 60 percent
Cold & Flu season is here! Visit the ABCNews.com OnCall+ Cold & Flu Center to get all your questions answered about these nasty viruses.